Collections类功能:
1.算法，比如排序(sort)，二分查找(binarySerach)，最大值(max)最小值(min)，翻转(reverse)，旋转(rotate),置换(shuffle),交换(swap)等。
2.提供对集合进行包装的静态方法。比如把指定的集合包装成线程安全的集合synchronizedXXX、包装成不可修改的集合unmodifiableXXX、包装成类型安全的集合checkedXXX等。
package java.util;
import java.io.Serializable;
import java.io.ObjectOutputStream;
import java.io.IOException;
import java.lang.reflect.Array;
public class Collections{
// Suppresses default constructor, ensuring non-instantiability.
private Collections() {
}
// 算法
/*
* 算法需要用到的一些参数。所有的关于List的算法都有两种实现，一种是适合随机访问的List，另一种是适合连续访问的。
*/
private static final int BINARYSEARCH_THRESHOLD = 5000;
private static final int REVERSE_THRESHOLD = 18;
private static final int SHUFFLE_THRESHOLD = 5;
private static final int FILL_THRESHOLD = 25;
private static final int ROTATE_THRESHOLD = 100;
private static final int COPY_THRESHOLD = 10;
private static final int REPLACEALL_THRESHOLD = 11;
private static final int INDEXOFSUBLIST_THRESHOLD = 35;
/**
* List中的所有元素必须实现Comparable接口,即每个 元素必须是可比的。
* 算法的实现原理为：
* 把指定的List转化为一个对象数组，对数组进行排序，然后迭代List的每一个元素，
* 在同样的位置重新设置数组中排好序的元素
*/
public static <T extends Comparable<? super T>> void sort(List<T> list) {
Object[] a = list.toArray();//转化为对象数组
Arrays.sort(a); //对数组排序，使用了归并排序.对此归并的
ListIterator<T> i = list.listIterator();
for (int j=0; j<a.length; j++) {
//迭代元素
i.next();
i.set((T)a[j]);//在同样的位置重设排好序的值
}
}
/**
* 传一个实现了Comparator接口的对象进来。
* c.compare(o1,o2);来比较两个元素
*/
public static <T> void sort(List<T> list, Comparator<? super T> c) {
Object[] a = list.toArray();
Arrays.sort(a, (Comparator)c);
ListIterator i = list.listIterator();
for (int j=0; j<a.length; j++) {
i.next();
i.set(a[j]);
}
}
/**
*
* 使用二分查找在指定List中查找指定元素key。
* List中的元素必须是有序的。如果List中有多个key，不能确保哪个key值被找到。
* 如果List不是有序的，返回的值没有任何意义
*
* 对于随机访问列表来说，时间复杂度为O(log(n)),比如1024个数只需要查找log2(1024)=10次，
* log2(n)是最坏的情况，即最坏的情况下都只需要找10次
* 对于链表来说，查找中间元素的时间复杂度为O(n),元素比较的时间复杂度为O(log(n))
*
* @return 查找元素的索引。如果返回的是负数表明找不到此元素，但可以用返回值计算
* 应该将key插入到集合什么位置，任然能使集合有序(如果需要插入key值的话)。
* 公式：point = -i - 1
*
*/
public static <T> int binarySearch(List<? extends Comparable<? super T>> list, T key) {
if (list instanceof RandomAccess || list.size()<BINARYSEARCH_THRESHOLD)
return Collections.indexedBinarySearch(list, key);
else
return Collections.iteratorBinarySearch(list, key);
}
/**
* 使用索引化二分查找。
* size小于5000的链表也用此方法查找
*/
private static <T> int indexedBinarySearch(List<? extends Comparable<? super T>> list, T key){
int low = 0;
//元素所在范围的下界
int high = list.size()-1;//上界
while (low <= high) {
int mid = (low + high) >>> 1;
Comparable<? super T> midVal = list.get(mid);//中间值
int cmp = midVal.compareTo(key);//指定元素与中间值比较
if (cmp < 0)
low = mid + 1;//重新设置上界和下界
else if (cmp > 0)
high = mid - 1;
else
return mid; // key found
}
return -(low + 1); // key not found
}
/**
* 迭代式二分查找，线性查找，依次查找得中间值
*
*/
private static <T> int iteratorBinarySearch(List<? extends Comparable<? super T>> list, T key){
int low = 0;
int high = list.size()-1;
ListIterator<? extends Comparable<? super T>> i = list.listIterator();
while (low <= high) {
int mid = (low + high) >>> 1;
Comparable<? super T> midVal = get(i, mid);
int cmp = midVal.compareTo(key);
if (cmp < 0)
low = mid + 1;
else if (cmp > 0)
high = mid - 1;
else
return mid; // key found
}
return -(low + 1); // key not found
}
private static <T> T get(ListIterator<? extends T> i, int index) {
T obj = null;
int pos = i.nextIndex(); //根据当前迭代器的位置确定是向前还是向后遍历找中间值
if (pos <= index) {
do {
obj = i.next();
} while (pos++ < index);
} else {
do {
obj = i.previous();
} while (--pos > index);
}
return obj;
}
/**
* 提供实现了Comparator接口的对象比较元素
*/
public static <T> int binarySearch(List<? extends T> list, T key, Comparator<? super T> c) {
if (c==null)
return binarySearch((List) list, key);
if (list instanceof RandomAccess || list.size()<BINARYSEARCH_THRESHOLD)
return Collections.indexedBinarySearch(list, key, c);
else
return Collections.iteratorBinarySearch(list, key, c);
}
private static <T> int indexedBinarySearch(List<? extends T> l, T key, Comparator<? super T> c) {
int low = 0;
int high = l.size()-1;
while (low <= high) {
int mid = (low + high) >>> 1;
T midVal = l.get(mid);
int cmp = c.compare(midVal, key);
if (cmp < 0)
low = mid + 1;
else if (cmp > 0)
high = mid - 1;
else
return mid; // key found
}
return -(low + 1); // key not found
}
private static <T> int iteratorBinarySearch(List<? extends T> l, T key, Comparator<? super T> c) {
int low = 0;
int high = l.size()-1;
ListIterator<? extends T> i = l.listIterator();
while (low <= high) {
int mid = (low + high) >>> 1;
T midVal = get(i, mid);
int cmp = c.compare(midVal, key);
if (cmp < 0)
low = mid + 1;
else if (cmp > 0)
high = mid - 1;
else
return mid; // key found
}
return -(low + 1); // key not found
}
private interface SelfComparable extends Comparable<SelfComparable> {}
/**
*
* 逆序排列指定列表中的元素
*/
public static void reverse(List<?> list) {
int size = list.size();
//如果是size小于18的链表或是基于随机访问的列表
if (size < REVERSE_THRESHOLD || list instanceof RandomAccess) {
for (int i=0, mid=size>>1, j=size-1; i<mid; i++, j--)//第一个与最后一个，依次交换
swap(list, i, j); //交换i和j位置的值
} else { //基于迭代器的逆序排列算法
ListIterator fwd = list.listIterator();
ListIterator rev = list.listIterator(size);
for (int i=0, mid=list.size()>>1; i<mid; i++) {//这..，一个思想你懂得
Object tmp = fwd.next();
fwd.set(rev.previous());
rev.set(tmp);
}
}
}
/**
*
* 对指定列表中的元素进行混排
*/
public static void shuffle(List<?> list) {
if (r == null) {
r = new Random();
}
shuffle(list, r);
}
private static Random r;
/**
*
* 提供一个随机数生成器对指定List进行混排
*
* 基本算法思想为：
* 逆向遍历list，从最后一个元素到第二个元素，然后重复交换当前位置
* 与随机产生的位置的元素值。
*
* 如果list不是基于随机访问并且其size>5,会先把List中的复制到数组中，
* 然后对数组进行混排，再把数组中的元素重新填入List中。
* 这样做为了避免迭代器大跨度查找元素影响效率
*/
public static void shuffle(List<?> list, Random rnd) {
int size = list.size();
if (size < SHUFFLE_THRESHOLD || list instanceof RandomAccess) {
for (int i=size; i>1; i--) //从i-1个位置开始与随机位置元素交换值
swap(list, i-1, rnd.nextInt(i));
} else {
Object arr[] = list.toArray(); //先转化为数组
//对数组进行混排
for (int i=size; i>1; i--)
swap(arr, i-1, rnd.nextInt(i));
// 然后把数组中的元素重新填入List
ListIterator it = list.listIterator();
for (int i=0; i<arr.length; i++) {
it.next();
it.set(arr[i]);
}
}
}
/**
* 交换List中两个位置的值
*/
public static void swap(List<?> list, int i, int j) {
final List l = list;
l.set(i, l.set(j, l.get(i)));//互换i和j位置的值
}
/**
* 交换数组俩位置的值。好熟悉啊
*/
private static void swap(Object[] arr, int i, int j) {
Object tmp = arr[i];
arr[i] = arr[j];
arr[j] = tmp;
}
/**
*
* 用obj替换List中的所有元素
* 依次遍历赋值即可
*/
public static <T> void fill(List<? super T> list, T obj) {
int size = list.size();
if (size < FILL_THRESHOLD || list instanceof RandomAccess) {
for (int i=0; i<size; i++)
list.set(i, obj);
} else {
ListIterator<? super T> itr = list.listIterator();
for (int i=0; i<size; i++) {
itr.next();
itr.set(obj);
}
}
}
/**
*
* 复制源列表的所有元素到目标列表，
* 如果src.size > dest.size 将抛出一个异常
* 如果src.size < dest.size dest中多出的元素将不受影响
* 同样是依次遍历赋值
*/
public static <T> void copy(List<? super T> dest, List<? extends T> src) {
int srcSize = src.size();
if (srcSize > dest.size())
throw new IndexOutOfBoundsException("Source does not fit in dest");
if (srcSize < COPY_THRESHOLD ||
(src instanceof RandomAccess && dest instanceof RandomAccess)) {
for (int i=0; i<srcSize; i++)
dest.set(i, src.get(i));
} else { //一个链表一个线性表也可以用迭代器赋值
ListIterator<? super T> di=dest.listIterator();
ListIterator<? extends T> si=src.listIterator();
for (int i=0; i<srcSize; i++) {
di.next();
di.set(si.next());
}
}
}
/**
*
* 返回集合中的最小元素。前提是其中的元素都是可比的，即实现了Comparable接口
* 找出一个通用的算法其实不容易，尽管它的思想不难。
* 反正要依次遍历完所有元素，所以直接用了迭代器
*/
public static <T extends Object & Comparable<? super T>> T min(Collection<? extends T> coll) {
Iterator<? extends T> i = coll.iterator();
T candidate = i.next();
while (i.hasNext()) {
T next = i.next();
if (next.compareTo(candidate) < 0)
candidate = next;
}
return candidate;
}
/**
* 根据提供的比较器求最小元素
*/
public static <T> T min(Collection<? extends T> coll, Comparator<? super T> comp) {
if (comp==null)
//返回默认比较器，其实默认比较器什么也不做，只是看集合元素是否实现了Comparable接口，
//否则抛出ClassCastException
return (T)min((Collection<SelfComparable>) (Collection) coll);
Iterator<? extends T> i = coll.iterator();
T candidate = i.next();//假设第一个元素为最小元素
while (i.hasNext()) {
T next = i.next();
if (comp.compare(next, candidate) < 0)
candidate = next;
}
return candidate;
}
/**
* 求集合中最大元素
*/
public static <T extends Object & Comparable<? super T>> T max(Collection<? extends T> coll) {
Iterator<? extends T> i = coll.iterator();
T candidate = i.next();
while (i.hasNext()) {
T next = i.next();
if (next.compareTo(candidate) > 0)
candidate = next;
}
return candidate;
}
/**
* 根据指定比较器求集合中最大元素
*/
public static <T> T max(Collection<? extends T> coll, Comparator<? super T> comp) {
if (comp==null)
return (T)max((Collection<SelfComparable>) (Collection) coll);
Iterator<? extends T> i = coll.iterator();
T candidate = i.next();
while (i.hasNext()) {
T next = i.next();
if (comp.compare(next, candidate) > 0)
candidate = next;
}
return candidate;
}
/**
*
* 旋转移位List中的元素通过指定的distance。每个元素移动后的位置为：
* (i + distance)%list.size.此方法不会改变列表的长度
*
* 比如，类表元素为： [t, a, n, k, s , w]
* 执行Collections.rotate(list, 2)或
* Collections.rotate(list, -4)后, list中的元素将变为
* [s, w, t, a, n , k]。可以这样理解：正数表示向后移，负数表示向前移
*
*/
public static void rotate(List<?> list, int distance) {
if (list instanceof RandomAccess || list.size() < ROTATE_THRESHOLD)
rotate1((List)list, distance);
else
rotate2((List)list, distance);
}
private static <T> void rotate1(List<T> list, int distance) {
int size = list.size();
if (size == 0)
return;
distance = distance % size; //distance始终处于0到size(不包括)之间
if (distance < 0)
distance += size; //还是以向后移来计算的
if (distance == 0)
return;
for (int cycleStart = 0, nMoved = 0; nMoved != size; cycleStart++) {
T displaced = list.get(cycleStart);
int i = cycleStart;
do {
i += distance; //求新位置
if (i >= size)
i -= size; //超出size就减去size
displaced = list.set(i, displaced);//为新位置赋原来的值
nMoved ++; //如果等于size证明全部替换完毕
} while(i != cycleStart); //依次类推，求新位置的新位置
}
}
private static void rotate2(List<?> list, int distance) {
int size = list.size();
if (size == 0)
return;
int mid = -distance % size;
if (mid < 0)
mid += size;
if (mid == 0)
return;
//好神奇啊
reverse(list.subList(0, mid));
reverse(list.subList(mid, size));
reverse(list);
}
/**
*
* 把指定集合中所有与oladVal相等的元素替换成newVal
* 只要list发生了改变就返回true
*/
public static <T> boolean replaceAll(List<T> list, T oldVal, T newVal) {
boolean result = false;
int size = list.size();
if (size < REPLACEALL_THRESHOLD || list instanceof RandomAccess) {
if (oldVal==null) {
for (int i=0; i<size; i++) {
if (list.get(i)==null) {
list.set(i, newVal);
result = true;
}
}
} else {
for (int i=0; i<size; i++) {
if (oldVal.equals(list.get(i))) {
list.set(i, newVal);
result = true;
}
}
}
} else {
ListIterator<T> itr=list.listIterator();
if (oldVal==null) {
for (int i=0; i<size; i++) {
if (itr.next()==null) {
itr.set(newVal);
result = true;
}
}
} else {
for (int i=0; i<size; i++) {
if (oldVal.equals(itr.next())) {
itr.set(newVal);
result = true;
}
}
}
}
return result;
}
/**
*
* target是否是source的子集，如果是返回target第一个元素的索引，
* 否则返回-1。
* 其实这里和串的模式匹配差不多。这里使用的是基本的回溯法。
*
*/
public static int indexOfSubList(List<?> source, List<?> target) {
int sourceSize = source.size();
int targetSize = target.size();
int maxCandidate = sourceSize - targetSize;
if (sourceSize < INDEXOFSUBLIST_THRESHOLD ||
(source instanceof RandomAccess&&target instanceof RandomAccess)) {
nextCand:for (int candidate = 0; candidate <= maxCandidate; candidate++) {
for (int i=0, j=candidate; i<targetSize; i++, j++)
if (!eq(target.get(i), source.get(j)))
continue nextCand; // 元素失配，跳到外部循环
return candidate; // All elements of candidate matched target
}
} else { // Iterator version of above algorithm
ListIterator<?> si = source.listIterator();
nextCand:for (int candidate = 0; candidate <= maxCandidate; candidate++) {
ListIterator<?> ti = target.listIterator();
for (int i=0; i<targetSize; i++) {
if (!eq(ti.next(), si.next())) {
// 回溯指针，然后跳到外部循环继续执行
for (int j=0; j<i; j++)
si.previous();
continue nextCand;
}
}
return candidate;
}
}
return -1; //没有找到匹配的子串返回-1
}
/**
* 如果有一个或多个字串，返回最后一个出现的子串的第一个元素的索引
*/
public static int lastIndexOfSubList(List<?> source, List<?> target) {
int sourceSize = source.size();
int targetSize = target.size();
int maxCandidate = sourceSize - targetSize;
if (sourceSize < INDEXOFSUBLIST_THRESHOLD ||
source instanceof RandomAccess) { // Index access version
nextCand:for (int candidate = maxCandidate; candidate >= 0; candidate--) {
for (int i=0, j=candidate; i<targetSize; i++, j++)
if (!eq(target.get(i), source.get(j)))//从source的maxCandidate位置开始比较。然后是maxCandidate-1，依次类推
continue nextCand; // Element mismatch, try next cand
return candidate; // All elements of candidate matched target
}
} else { // Iterator version of above algorithm
if (maxCandidate < 0)
return -1;
ListIterator<?> si = source.listIterator(maxCandidate);
nextCand: for (int candidate = maxCandidate; candidate >= 0; candidate--) {
ListIterator<?> ti = target.listIterator();
for (int i=0; i<targetSize; i++) {
if (!eq(ti.next(), si.next())) {
if (candidate != 0) {
// Back up source iterator to next candidate
for (int j=0; j<=i+1; j++)
si.previous();
}
continue nextCand;
}
}
return candidate;
}
}
return -1; // No candidate matched the target
}
// Unmodifiable Wrappers
/**
*
* 返回一个关于指定集合的不可修改的视图。
* 任何试图修改该视图的操作都将抛出一个UnsupportedOperationException
*
* Collection返回的视图的equals方法不是调用底层集合的equals方法
* 而是继承了Object的equals方法。hashCode方法也是一样的。
* 因为Set和List的equals方法并不相同。
*/
public static <T> Collection<T> unmodifiableCollection(Collection<? extends T> c) {
return new UnmodifiableCollection<T>(c);
}
static class UnmodifiableCollection<E> implements Collection<E>, Serializable {
// use serialVersionUID from JDK 1.2.2 for interoperability
private static final long serialVersionUID = 1820017752578914078L;
final Collection<? extends E> c;
UnmodifiableCollection(Collection<? extends E> c) {
if (c==null)
throw new NullPointerException();
this.c = c;
}
public int size()
{return c.size();}
public boolean isEmpty()
{return c.isEmpty();}
public boolean contains(Object o) {return c.contains(o);}
public Object[] toArray() {return c.toArray();}
public <T> T[] toArray(T[] a) {return c.toArray(a);}
public String toString() {return c.toString();}
public Iterator<E> iterator() {
return new Iterator<E>() {
Iterator<? extends E> i = c.iterator();
public boolean hasNext() {return i.hasNext();}
public E next()
{return i.next();}
public void remove() {//试图修改集合的操作都将抛出此异常
throw new UnsupportedOperationException();
}
};
}
public boolean add(E e){
throw new UnsupportedOperationException();
}
public boolean remove(Object o) {
throw new UnsupportedOperationException();
}
public boolean containsAll(Collection<?> coll) {
return c.containsAll(coll);
}
public boolean addAll(Collection<? extends E> coll) {
throw new UnsupportedOperationException();
}
public boolean removeAll(Collection<?> coll) {
throw new UnsupportedOperationException();
}
public boolean retainAll(Collection<?> coll) {
throw new UnsupportedOperationException();
}
public void clear() {
throw new UnsupportedOperationException();
}
}
/**
* 返回一个不可修改Set。
* 调用的是底层集合的equals方法
*/
public static <T> Set<T> unmodifiableSet(Set<? extends T> s) {
return new UnmodifiableSet<T>(s);
}
/**
* @serial include
*/
static class UnmodifiableSet<E> extends UnmodifiableCollection<E>
implements Set<E>, Serializable {
private static final long serialVersionUID = -9215047833775013803L;
UnmodifiableSet(Set<? extends E> s){super(s);}
public boolean equals(Object o) {return o == this || c.equals(o);}
public int hashCode()
{return c.hashCode();}
}
/**
* 返回一个不可修改的Sort Set
*/
public static <T> SortedSet<T> unmodifiableSortedSet(SortedSet<T> s) {
return new UnmodifiableSortedSet<T>(s);
}
static class UnmodifiableSortedSet<E>
extends UnmodifiableSet<E>
implements SortedSet<E>, Serializable {
private static final long serialVersionUID = -4929149591599911165L;
private final SortedSet<E> ss;
UnmodifiableSortedSet(SortedSet<E> s) {super(s); ss = s;}
public Comparator<? super E> comparator() {return ss.comparator();}
public SortedSet<E> subSet(E fromElement, E toElement) {
return new UnmodifiableSortedSet<E>(ss.subSet(fromElement,toElement));
}
public SortedSet<E> headSet(E toElement) {
return new UnmodifiableSortedSet<E>(ss.headSet(toElement));
}
public SortedSet<E> tailSet(E fromElement) {
return new UnmodifiableSortedSet<E>(ss.tailSet(fromElement));
}
public E first() {return ss.first();}
public E last() {return ss.last();}
}
/**
* 返回一个 不可修改的List
* 如果原List实现了RandomAccess接口，返回的List也将实现此接口
*/
public static <T> List<T> unmodifiableList(List<? extends T> list) {
return (list instanceof RandomAccess ?
new UnmodifiableRandomAccessList<T>(list) :
new UnmodifiableList<T>(list));
}
static class UnmodifiableList<E> extends UnmodifiableCollection<E>
implements List<E> {
static final long serialVersionUID = -283967356065247728L;
final List<? extends E> list;
UnmodifiableList(List<? extends E> list) {
super(list);
this.list = list;
}
public boolean equals(Object o) {return o == this || list.equals(o);}
public int hashCode()
{return list.hashCode();}
public E get(int index) {return list.get(index);}
public E set(int index, E element) {
throw new UnsupportedOperationException();
}
public void add(int index, E element) {
throw new UnsupportedOperationException();
}
public E remove(int index) {
throw new UnsupportedOperationException();
}
public int indexOf(Object o) {return list.indexOf(o);}
public int lastIndexOf(Object o) {return list.lastIndexOf(o);}
public boolean addAll(int index, Collection<? extends E> c) {
throw new UnsupportedOperationException();
}
public ListIterator<E> listIterator()
{return listIterator(0);}
public ListIterator<E> listIterator(final int index) {
return new ListIterator<E>() {
ListIterator<? extends E> i = list.listIterator(index);
public boolean hasNext() {return i.hasNext();}
public E next() {return i.next();}
public boolean hasPrevious() {return i.hasPrevious();}
public E previous() {return i.previous();}
public int nextIndex() {return i.nextIndex();}
public int previousIndex() {return i.previousIndex();}
public void remove() {
throw new UnsupportedOperationException();
}
public void set(E e) {
throw new UnsupportedOperationException();
}
public void add(E e) {
throw new UnsupportedOperationException();
}
};
}
public List<E> subList(int fromIndex, int toIndex) {
return new UnmodifiableList<E>(list.subList(fromIndex, toIndex));
}
/**
* UnmodifiableRandomAccessList instances are serialized as
* UnmodifiableList instances to allow them to be deserialized
* in pre-1.4 JREs (which do not have UnmodifiableRandomAccessList).
* This method inverts the transformation. As a beneficial
* side-effect, it also grafts the RandomAccess marker onto
* UnmodifiableList instances that were serialized in pre-1.4 JREs.
*
* Note: Unfortunately, UnmodifiableRandomAccessList instances
* serialized in 1.4.1 and deserialized in 1.4 will become
* UnmodifiableList instances, as this method was missing in 1.4.
* 这个，自己看吧...
*/
private Object readResolve() {
return (list instanceof RandomAccess
? new UnmodifiableRandomAccessList<E>(list)
: this);
}
}
static class UnmodifiableRandomAccessList<E> extends UnmodifiableList<E>
implements RandomAccess{
UnmodifiableRandomAccessList(List<? extends E> list) {
super(list);
}
public List<E> subList(int fromIndex, int toIndex) {
return new UnmodifiableRandomAccessList<E>(
list.subList(fromIndex, toIndex));
}
private static final long serialVersionUID = -2542308836966382001L;
/**
* Allows instances to be deserialized in pre-1.4 JREs (which do
* not have UnmodifiableRandomAccessList). UnmodifiableList has
* a readResolve method that inverts this transformation upon
* deserialization.
*/
private Object writeReplace() {
return new UnmodifiableList<E>(list);
}
}
/**
* 返回一个不可修改的map
*/
public static <K,V> Map<K,V> unmodifiableMap(Map<? extends K, ? extends V> m) {
return new UnmodifiableMap<K,V>(m);
}
private static class UnmodifiableMap<K,V> implements Map<K,V>, Serializable {
// use serialVersionUID from JDK 1.2.2 for interoperability
private static final long serialVersionUID = -1034234728574286014L;
private final Map<? extends K, ? extends V> m;
UnmodifiableMap(Map<? extends K, ? extends V> m) {
if (m==null)
throw new NullPointerException();
this.m = m;
}
public int size()
{return m.size();}
public boolean isEmpty()
{return m.isEmpty();}
public boolean containsKey(Object key) {return m.containsKey(key);}
public boolean containsValue(Object val) {return m.containsValue(val);}
public V get(Object key)
{return m.get(key);}
public V put(K key, V value) {
throw new UnsupportedOperationException();
}
public V remove(Object key) {
throw new UnsupportedOperationException();
}
public void putAll(Map<? extends K, ? extends V> m) {
throw new UnsupportedOperationException();
}
public void clear() {
throw new UnsupportedOperationException();
}
private transient Set<K> keySet = null;
private transient Set<Map.Entry<K,V>> entrySet = null;
private transient Collection<V> values = null;
//返回的key集也是不可修改的
public Set<K> keySet() {
if (keySet==null)
keySet = unmodifiableSet(m.keySet());
return keySet;
}
//EntrySet被重新进行包装
public Set<Map.Entry<K,V>> entrySet() {
if (entrySet==null)
entrySet = new UnmodifiableEntrySet<K,V>(m.entrySet());
return entrySet;
}
public Collection<V> values() {
if (values==null)
values = unmodifiableCollection(m.values());
return values;
}
public boolean equals(Object o) {return o == this || m.equals(o);}
public int hashCode() {return m.hashCode();}
public String toString() {return m.toString();}
/**
*
* 需要重新包装返回的EntrySet对象
*/
static class UnmodifiableEntrySet<K,V> extends UnmodifiableSet<Map.Entry<K,V>> {
private static final long serialVersionUID = 7854390611657943733L;
UnmodifiableEntrySet(Set<? extends Map.Entry<? extends K, ? extends V>> s) {
super((Set)s);
}
public Iterator<Map.Entry<K,V>> iterator() {
return new Iterator<Map.Entry<K,V>>() {
//父类UnmodifiableColletion的c
Iterator<? extends Map.Entry<? extends K, ? extends V>> i = c.iterator();
public boolean hasNext() {
return i.hasNext();
}
public Map.Entry<K,V> next() {
return new UnmodifiableEntry<K,V>(i.next());
}
public void remove() {
throw new UnsupportedOperationException();
}
};
}
public Object[] toArray() {
Object[] a = c.toArray();
for (int i=0; i<a.length; i++)
a[i] = new UnmodifiableEntry<K,V>((Map.Entry<K,V>)a[i]);
return a;
}
public <T> T[] toArray(T[] a) {
Object[] arr = c.toArray(a.length==0 ? a : Arrays.copyOf(a, 0));
for (int i=0; i<arr.length; i++)
arr[i] = new UnmodifiableEntry<K,V>((Map.Entry<K,V>)arr[i]);
if (arr.length > a.length)
return (T[])arr;
System.arraycopy(arr, 0, a, 0, arr.length);
if (a.length > arr.length)
a[arr.length] = null;
return a;
}
public boolean contains(Object o) {
if (!(o instanceof Map.Entry))
return false;
return c.contains(new UnmodifiableEntry<K,V>((Map.Entry<K,V>) o));
}
public boolean containsAll(Collection<?> coll) {
Iterator<?> e = coll.iterator();
while (e.hasNext())
if (!contains(e.next())) // Invokes safe contains() above
return false;
return true;
}
public boolean equals(Object o) {
if (o == this)
return true;
if (!(o instanceof Set))
return false;
Set s = (Set) o;
if (s.size() != c.size())
return false;
return containsAll(s); // Invokes safe containsAll() above
}
/**
* 重新包装Entry。
*/
private static class UnmodifiableEntry<K,V> implements Map.Entry<K,V> {
private Map.Entry<? extends K, ? extends V> e;
UnmodifiableEntry(Map.Entry<? extends K, ? extends V> e) {this.e = e;}
public K getKey() {return e.getKey();}
public V getValue() {return e.getValue();}
public V setValue(V value) {
//调用set方法将抛出一个异常
throw new UnsupportedOperationException();
}
public int hashCode() {return e.hashCode();}
public boolean equals(Object o) {
if (!(o instanceof Map.Entry))
return false;
Map.Entry t = (Map.Entry)o;
return eq(e.getKey(), t.getKey()) &&
eq(e.getValue(), t.getValue());
}
public String toString() {return e.toString();}
}
}
}
/**
* 返回一个不可修改的SortedMap
*/
public static <K,V> SortedMap<K,V> unmodifiableSortedMap(SortedMap<K, ? extends V> m) {
return new UnmodifiableSortedMap<K,V>(m);
}
static class UnmodifiableSortedMap<K,V> extends UnmodifiableMap<K,V>
implements SortedMap<K,V>, Serializable {
private static final long serialVersionUID = -8806743815996713206L;
private final SortedMap<K, ? extends V> sm;
UnmodifiableSortedMap(SortedMap<K, ? extends V> m) {super(m); sm = m;}
public Comparator<? super K> comparator() {return sm.comparator();}
public SortedMap<K,V> subMap(K fromKey, K toKey) {
return new UnmodifiableSortedMap<K,V>(sm.subMap(fromKey, toKey));
}
public SortedMap<K,V> headMap(K toKey) {
return new UnmodifiableSortedMap<K,V>(sm.headMap(toKey));
}
public SortedMap<K,V> tailMap(K fromKey) {
return new UnmodifiableSortedMap<K,V>(sm.tailMap(fromKey));
}
public K firstKey() {return sm.firstKey();}
public K lastKey() {return sm.lastKey();}
}
// 同步包装
/**
*
* 返回一个线程安全的集合
* 但是当用户遍历此集合时，需要手动进行同步
* Collection c = Collections.synchronizedCollection(myCollection);
* ...
* synchronized(c) {
* Iterator i = c.iterator(); // Must be in the synchronized block
* while (i.hasNext())
* foo(i.next());
* }
*
*/
public static <T> Collection<T> synchronizedCollection(Collection<T> c) {
return new SynchronizedCollection<T>(c);
}
static <T> Collection<T> synchronizedCollection(Collection<T> c, Object mutex) {
return new SynchronizedCollection<T>(c, mutex);
}
/**
* @serial include
*/
static class SynchronizedCollection<E> implements Collection<E>, Serializable {
// use serialVersionUID from JDK 1.2.2 for interoperability
private static final long serialVersionUID = 3053995032091335093L;
final Collection<E> c; // 返回的集合
final Object mutex; // 需要同步的对象
SynchronizedCollection(Collection<E> c) {
if (c==null)
throw new NullPointerException();
this.c = c;
mutex = this;
}
SynchronizedCollection(Collection<E> c, Object mutex) {
this.c = c;
this.mutex = mutex;
}
public int size() {
synchronized(mutex) {return c.size();}
}
public boolean isEmpty() {
synchronized(mutex) {return c.isEmpty();}
}
public boolean contains(Object o) {
synchronized(mutex) {return c.contains(o);}
}
public Object[] toArray() {
synchronized(mutex) {return c.toArray();}
}
public <T> T[] toArray(T[] a) {
synchronized(mutex) {return c.toArray(a);}
}
public Iterator<E> iterator() {
return c.iterator(); // 必须用户自己手动同步
}
public boolean add(E e) {
synchronized(mutex) {return c.add(e);}
}
public boolean remove(Object o) {
synchronized(mutex) {return c.remove(o);}
}
public boolean containsAll(Collection<?> coll) {
synchronized(mutex) {return c.containsAll(coll);}
}
public boolean addAll(Collection<? extends E> coll) {
synchronized(mutex) {return c.addAll(coll);}
}
public boolean removeAll(Collection<?> coll) {
synchronized(mutex) {return c.removeAll(coll);}
}
public boolean retainAll(Collection<?> coll) {
synchronized(mutex) {return c.retainAll(coll);}
}
public void clear() {
synchronized(mutex) {c.clear();}
}
public String toString() {
synchronized(mutex) {return c.toString();}
}
private void writeObject(ObjectOutputStream s) throws IOException {
synchronized(mutex) {s.defaultWriteObject();}
}
}
/**
* 返回一个线程安全的Set
*/
public static <T> Set<T> synchronizedSet(Set<T> s) {
return new SynchronizedSet<T>(s);
}
static <T> Set<T> synchronizedSet(Set<T> s, Object mutex) {
return new SynchronizedSet<T>(s, mutex);
}
/**
* @serial include
*/
static class SynchronizedSet<E> extends SynchronizedCollection<E> implements Set<E> {
private static final long serialVersionUID = 487447009682186044L;
SynchronizedSet(Set<E> s) {
super(s);
}
SynchronizedSet(Set<E> s, Object mutex) {
super(s, mutex);
}
public boolean equals(Object o) {
synchronized(mutex) {return c.equals(o);}
}
public int hashCode() {
synchronized(mutex) {return c.hashCode();}
}
}
/**
* 返回一个线程安全的SortedSet
*/
public static <T> SortedSet<T> synchronizedSortedSet(SortedSet<T> s) {
return new SynchronizedSortedSet<T>(s);
}
/**
* @serial include
*/
static class SynchronizedSortedSet<E> extends SynchronizedSet<E>implements SortedSet<E>{
private static final long serialVersionUID = 8695801310862127406L;
final private SortedSet<E> ss;
SynchronizedSortedSet(SortedSet<E> s) {
super(s);
ss = s;
}
SynchronizedSortedSet(SortedSet<E> s, Object mutex) {
super(s, mutex);
ss = s;
}
public Comparator<? super E> comparator() {
synchronized(mutex) {return ss.comparator();}
}
public SortedSet<E> subSet(E fromElement, E toElement) {
synchronized(mutex) {
return new SynchronizedSortedSet<E>(
ss.subSet(fromElement, toElement), mutex);
}
}
public SortedSet<E> headSet(E toElement) {
synchronized(mutex) {
return new SynchronizedSortedSet<E>(ss.headSet(toElement), mutex);
}
}
public SortedSet<E> tailSet(E fromElement) {
synchronized(mutex) {
return new SynchronizedSortedSet<E>(ss.tailSet(fromElement),mutex);
}
}
public E first() {
synchronized(mutex) {return ss.first();}
}
public E last() {
synchronized(mutex) {return ss.last();}
}
}
/**
* 返回一个线程安全的List，
* 如果List是基于随机访问的，返回的List同样实现了RandomAccess接口
*/
public static <T> List<T> synchronizedList(List<T> list) {
return (list instanceof RandomAccess ?
new SynchronizedRandomAccessList<T>(list) :
new SynchronizedList<T>(list));
}
static <T> List<T> synchronizedList(List<T> list, Object mutex) {
return (list instanceof RandomAccess ?
new SynchronizedRandomAccessList<T>(list, mutex) :
new SynchronizedList<T>(list, mutex));
}
/**
* @serial include
*/
static class SynchronizedList<E>extends SynchronizedCollection<E> implements List<E> {
static final long serialVersionUID = -7754090372962971524L;
final List<E> list;
SynchronizedList(List<E> list) {
super(list);
this.list = list;
}
SynchronizedList(List<E> list, Object mutex) {
super(list, mutex);
this.list = list;
}
public boolean equals(Object o) {
synchronized(mutex) {return list.equals(o);}
}
public int hashCode() {
synchronized(mutex) {return list.hashCode();}
}
public E get(int index) {
synchronized(mutex) {return list.get(index);}
}
public E set(int index, E element) {
synchronized(mutex) {return list.set(index, element);}
}
public void add(int index, E element) {
synchronized(mutex) {list.add(index, element);}
}
public E remove(int index) {
synchronized(mutex) {return list.remove(index);}
}
public int indexOf(Object o) {
synchronized(mutex) {return list.indexOf(o);}
}
public int lastIndexOf(Object o) {
synchronized(mutex) {return list.lastIndexOf(o);}
}
public boolean addAll(int index, Collection<? extends E> c) {
synchronized(mutex) {return list.addAll(index, c);}
}
public ListIterator<E> listIterator() {
return list.listIterator(); // Must be manually synched by user
}
public ListIterator<E> listIterator(int index) {
return list.listIterator(index); // Must be manually synched by user
}
public List<E> subList(int fromIndex, int toIndex) {
synchronized(mutex) {
return new SynchronizedList<E>(list.subList(fromIndex, toIndex),
mutex);
}
}
private Object readResolve() {
return (list instanceof RandomAccess
? new SynchronizedRandomAccessList<E>(list)
: this);
}
}
/**
* @serial include
*/
static class SynchronizedRandomAccessList<E>extends SynchronizedList<E>
implements RandomAccess {
SynchronizedRandomAccessList(List<E> list) {
super(list);
}
SynchronizedRandomAccessList(List<E> list, Object mutex) {
super(list, mutex);
}
public List<E> subList(int fromIndex, int toIndex) {
synchronized(mutex) {
return new SynchronizedRandomAccessList<E>(
list.subList(fromIndex, toIndex), mutex);
}
}
static final long serialVersionUID = 1530674583602358482L;
private Object writeReplace() {
return new SynchronizedList<E>(list);
}
}
/**
* 返回一个线程安全的map
*/
public static <K,V> Map<K,V> synchronizedMap(Map<K,V> m) {
return new SynchronizedMap<K,V>(m);
}
/**
* @serial include
*/
private static class SynchronizedMap<K,V>
implements Map<K,V>, Serializable {
// use serialVersionUID from JDK 1.2.2 for interoperability
private static final long serialVersionUID = 1978198479659022715L;
private final Map<K,V> m; // Backing Map
final Object mutex; // Object on which to synchronize
SynchronizedMap(Map<K,V> m) {
if (m==null)
throw new NullPointerException();
this.m = m;
mutex = this;
}
SynchronizedMap(Map<K,V> m, Object mutex) {
this.m = m;
this.mutex = mutex;
}
public int size() {
synchronized(mutex) {return m.size();}
}
public boolean isEmpty(){
synchronized(mutex) {return m.isEmpty();}
}
public boolean containsKey(Object key) {
synchronized(mutex) {return m.containsKey(key);}
}
public boolean containsValue(Object value){
synchronized(mutex) {return m.containsValue(value);}
}
public V get(Object key) {
synchronized(mutex) {return m.get(key);}
}
public V put(K key, V value) {
synchronized(mutex) {return m.put(key, value);}
}
public V remove(Object key) {
synchronized(mutex) {return m.remove(key);}
}
public void putAll(Map<? extends K, ? extends V> map) {
synchronized(mutex) {m.putAll(map);}
}
public void clear() {
synchronized(mutex) {m.clear();}
}
private transient Set<K> keySet = null;
private transient Set<Map.Entry<K,V>> entrySet = null;
private transient Collection<V> values = null;
public Set<K> keySet() {
synchronized(mutex) {
if (keySet==null)
keySet = new SynchronizedSet<K>(m.keySet(), mutex);
return keySet;
}
}
public Set<Map.Entry<K,V>> entrySet() {
synchronized(mutex) {
if (entrySet==null)
entrySet = new SynchronizedSet<Map.Entry<K,V>>(m.entrySet(), mutex);
return entrySet;
}
}
public Collection<V> values() {
synchronized(mutex) {
if (values==null)
values = new SynchronizedCollection<V>(m.values(), mutex);
return values;
}
}
public boolean equals(Object o) {
synchronized(mutex) {return m.equals(o);}
}
public int hashCode() {
synchronized(mutex) {return m.hashCode();}
}
public String toString() {
synchronized(mutex) {return m.toString();}
}
private void writeObject(ObjectOutputStream s) throws IOException {
synchronized(mutex) {s.defaultWriteObject();}
}
}
/**
* 返回一个线程安全的SortedSet
*/
public static <K,V> SortedMap<K,V> synchronizedSortedMap(SortedMap<K,V> m) {
return new SynchronizedSortedMap<K,V>(m);
}
/**
* @serial include
*/
static class SynchronizedSortedMap<K,V>
extends SynchronizedMap<K,V>
implements SortedMap<K,V>
{
private static final long serialVersionUID = -8798146769416483793L;
private final SortedMap<K,V> sm;
SynchronizedSortedMap(SortedMap<K,V> m) {
super(m);
sm = m;
}
SynchronizedSortedMap(SortedMap<K,V> m, Object mutex) {
super(m, mutex);
sm = m;
}
public Comparator<? super K> comparator() {
synchronized(mutex) {return sm.comparator();}
}
public SortedMap<K,V> subMap(K fromKey, K toKey) {
synchronized(mutex) {
return new SynchronizedSortedMap<K,V>(
sm.subMap(fromKey, toKey), mutex);
}
}
public SortedMap<K,V> headMap(K toKey) {
synchronized(mutex) {
return new SynchronizedSortedMap<K,V>(sm.headMap(toKey), mutex);
}
}
public SortedMap<K,V> tailMap(K fromKey) {
synchronized(mutex) {
return new SynchronizedSortedMap<K,V>(sm.tailMap(fromKey),mutex);
}
}
public K firstKey() {
synchronized(mutex) {return sm.firstKey();}
}
public K lastKey() {
synchronized(mutex) {return sm.lastKey();}
}
}
// Dynamically typesafe collection wrappers
/**
*
* 返回一个动态的类型安全的集合。任何试图插入错误类型的元素的操作将立刻抛出
* ClassCastException
* 动态类型安全视图的一个主要作用是用作debug调试，
* 因为它能正确反映出出错的位置。
* 例如：ArrayList<String> strings = new ArrayList<String>();
* ArrayList rawList = strings;
* rawList.add(new Date());
* add方法并不进行类型检查，所以存入了非String的对象。只有在重新获取该对象
* 转化为String类型的时候才抛出异常。
* 而动态类型安全的集合能在add时就会抛出ClassCastException。
* 这种方法的优点是错误可以在正确的位置被报告
*
*
*/
public static <E> Collection<E> checkedCollection(Collection<E> c,Class<E> type) {
return new CheckedCollection<E>(c, type);
}
/**
* @serial include
*/
static class CheckedCollection<E> implements Collection<E>, Serializable {
private static final long serialVersionUID = 1578914078182001775L;
final Collection<E> c;
final Class<E> type;
void typeCheck(Object o) {
if (!type.isInstance(o)) //o是否能被转换成type类型
throw new ClassCastException("Attempt to insert " +
o.getClass() + " element into collection with element type "
+ type);
}
CheckedCollection(Collection<E> c, Class<E> type) {
if (c==null || type == null)
throw new NullPointerException();
this.c = c;
this.type = type;
}
public int size() { return c.size(); }
public boolean isEmpty() { return c.isEmpty(); }
public boolean contains(Object o) { return c.contains(o); }
public Object[] toArray() { return c.toArray(); }
public <T> T[] toArray(T[] a) { return c.toArray(a); }
public String toString() { return c.toString(); }
public boolean remove(Object o) { return c.remove(o); }
public boolean containsAll(Collection<?> coll) {
return c.containsAll(coll);
}
public boolean removeAll(Collection<?> coll) {
return c.removeAll(coll);
}
public boolean retainAll(Collection<?> coll) {
return c.retainAll(coll);
}
public void clear() {
c.clear();
}
public Iterator<E> iterator() {
return new Iterator<E>() {
private final Iterator<E> it = c.iterator();
public boolean hasNext() { return it.hasNext(); }
public E next() { return it.next(); }
public void remove() { it.remove(); }};
}
public boolean add(E e){
typeCheck(e); //添加元素需要进行类型检查
return c.add(e);
}
public boolean addAll(Collection<? extends E> coll) {
E[] a = null;
try {
a = coll.toArray(zeroLengthElementArray());//根据zero数组的类型来转换集合为数组。如果coll中含有其他类型这里就会抛出异常
} catch (ArrayStoreException e) {
throw new ClassCastException();
}
boolean result = false;
for (E e : a)
result |= c.add(e); //只要集合发生了改变就返回true
return result;
}
private E[] zeroLengthElementArray = null; // Lazily initialized
/*
* We don't need locking or volatile, because it's OK if we create
* several zeroLengthElementArrays, and they're immutable.
*/
E[] zeroLengthElementArray() {
if (zeroLengthElementArray == null)
zeroLengthElementArray = (E[]) Array.newInstance(type, 0);
return zeroLengthElementArray;
}
}
/**
* 返回一个会检查类型的集合Set
*/
public static <E> Set<E> checkedSet(Set<E> s, Class<E> type) {
return new CheckedSet<E>(s, type);
}
/**
* @serial include
*/
static class CheckedSet<E> extends CheckedCollection<E>
implements Set<E>, Serializable{
private static final long serialVersionUID = 4694047833775013803L;
CheckedSet(Set<E> s, Class<E> elementType) { super(s, elementType); }
public boolean equals(Object o) { return o == this || c.equals(o); }
public int hashCode() { return c.hashCode(); }
}
/**
* 返回一个类型安全的集合SortedSet
*/
public static <E> SortedSet<E> checkedSortedSet(SortedSet<E> s,Class<E> type) {
return new CheckedSortedSet<E>(s, type);
}
/**
* @serial include
*/
static class CheckedSortedSet<E> extends CheckedSet<E>
implements SortedSet<E>, Serializable{
private static final long serialVersionUID = 1599911165492914959L;
private final SortedSet<E> ss;
CheckedSortedSet(SortedSet<E> s, Class<E> type) {
super(s, type);
ss = s;
}
public Comparator<? super E> comparator() { return ss.comparator(); }
public E first() { return ss.first(); }
public E last() { return ss.last(); }
public SortedSet<E> subSet(E fromElement, E toElement) {
return new CheckedSortedSet<E>(ss.subSet(fromElement,toElement),
type);
}
public SortedSet<E> headSet(E toElement) {
return new CheckedSortedSet<E>(ss.headSet(toElement), type);
}
public SortedSet<E> tailSet(E fromElement) {
return new CheckedSortedSet<E>(ss.tailSet(fromElement), type);
}
}
/**
* 返回一个类型安全的集合List
*/
public static <E> List<E> checkedList(List<E> list, Class<E> type) {
return (list instanceof RandomAccess ?
new CheckedRandomAccessList<E>(list, type) :
new CheckedList<E>(list, type));
}
/**
* @serial include
*/
static class CheckedList<E> extends CheckedCollection<E>
implements List<E>
{
static final long serialVersionUID = 65247728283967356L;
final List<E> list;
CheckedList(List<E> list, Class<E> type) {
super(list, type);
this.list = list;
}
public boolean equals(Object o) { return o == this || list.equals(o); }
public int hashCode() { return list.hashCode(); }
public E get(int index) { return list.get(index); }
public E remove(int index) { return list.remove(index); }
public int indexOf(Object o) { return list.indexOf(o); }
public int lastIndexOf(Object o) { return list.lastIndexOf(o); }
public E set(int index, E element) {
typeCheck(element);
return list.set(index, element);
}
public void add(int index, E element) {
typeCheck(element);
list.add(index, element);
}
public boolean addAll(int index, Collection<? extends E> c) {
// See CheckCollection.addAll, above, for an explanation
E[] a = null;
try {
a = c.toArray(zeroLengthElementArray());
} catch (ArrayStoreException e) {
throw new ClassCastException();
}
return list.addAll(index, Arrays.asList(a));
}
public ListIterator<E> listIterator() { return listIterator(0); }
public ListIterator<E> listIterator(final int index) {
return new ListIterator<E>() {
ListIterator<E> i = list.listIterator(index);
public boolean hasNext() { return i.hasNext(); }
public E next() { return i.next(); }
public boolean hasPrevious() { return i.hasPrevious(); }
public E previous() { return i.previous(); }
public int nextIndex() { return i.nextIndex(); }
public int previousIndex() { return i.previousIndex(); }
public void remove() { i.remove(); }
public void set(E e) {
typeCheck(e);
i.set(e);
}
public void add(E e) {
typeCheck(e);
i.add(e);
}
};
}
public List<E> subList(int fromIndex, int toIndex) {
return new CheckedList<E>(list.subList(fromIndex, toIndex), type);
}
}
/**
* @serial include
*/
static class CheckedRandomAccessList<E> extends CheckedList<E>
implements RandomAccess
{
private static final long serialVersionUID = 1638200125423088369L;
CheckedRandomAccessList(List<E> list, Class<E> type) {
super(list, type);
}
public List<E> subList(int fromIndex, int toIndex) {
return new CheckedRandomAccessList<E>(
list.subList(fromIndex, toIndex), type);
}
}
/**
* 返回一个类型安全的集合Map
*/
public static <K, V> Map<K, V> checkedMap(Map<K, V> m, Class<K> keyType,
Class<V> valueType) {
return new CheckedMap<K,V>(m, keyType, valueType);
}
/**
* @serial include
*/
private static class CheckedMap<K,V> implements Map<K,V>,
Serializable
{
private static final long serialVersionUID = 5742860141034234728L;
private final Map<K, V> m;
final Class<K> keyType;
final Class<V> valueType;
//需要对key与value都进行类型检查
private void typeCheck(Object key, Object value) {
if (!keyType.isInstance(key))
throw new ClassCastException("Attempt to insert " +
key.getClass() + " key into collection with key type "
+ keyType);
if (!valueType.isInstance(value))
throw new ClassCastException("Attempt to insert " +
value.getClass() +" value into collection with value type "
+ valueType);
}
CheckedMap(Map<K, V> m, Class<K> keyType, Class<V> valueType) {
if (m == null || keyType == null || valueType == null)
throw new NullPointerException();
this.m = m;
this.keyType = keyType;
this.valueType = valueType;
}
public int size() { return m.size(); }
public boolean isEmpty() { return m.isEmpty(); }
public boolean containsKey(Object key) { return m.containsKey(key); }
public boolean containsValue(Object v) { return m.containsValue(v); }
public V get(Object key) { return m.get(key); }
public V remove(Object key) { return m.remove(key); }
public void clear() { m.clear(); }
public Set<K> keySet() { return m.keySet(); }
public Collection<V> values() { return m.values(); }
public boolean equals(Object o) { return o == this || m.equals(o); }
public int hashCode() { return m.hashCode(); }
public String toString() { return m.toString(); }
public V put(K key, V value) {
typeCheck(key, value);
return m.put(key, value);
}
public void putAll(Map<? extends K, ? extends V> t) {
// See CheckCollection.addAll, above, for an explanation
K[] keys = null;
try {
keys = t.keySet().toArray(zeroLengthKeyArray());
} catch (ArrayStoreException e) {
throw new ClassCastException();
}
V[] values = null;
try {
values = t.values().toArray(zeroLengthValueArray());
} catch (ArrayStoreException e) {
throw new ClassCastException();
}
if (keys.length != values.length)
throw new ConcurrentModificationException();
for (int i = 0; i < keys.length; i++)
m.put(keys[i], values[i]);
}
// Lazily initialized
private K[] zeroLengthKeyArray = null;
private V[] zeroLengthValueArray = null;
/*
* We don't need locking or volatile, because it's OK if we create
* several zeroLengthValueArrays, and they're immutable.
*/
private K[] zeroLengthKeyArray() {
if (zeroLengthKeyArray == null)
zeroLengthKeyArray = (K[]) Array.newInstance(keyType, 0);
return zeroLengthKeyArray;
}
private V[] zeroLengthValueArray() {
if (zeroLengthValueArray == null)
zeroLengthValueArray = (V[]) Array.newInstance(valueType, 0);
return zeroLengthValueArray;
}
private transient Set<Map.Entry<K,V>> entrySet = null;
public Set<Map.Entry<K,V>> entrySet() {
if (entrySet==null)
entrySet = new CheckedEntrySet<K,V>(m.entrySet(), valueType);
return entrySet;
}
/**
* We need this class in addition to CheckedSet as Map.Entry permits
* modification of the backing Map via the setValue operation. This
* class is subtle: there are many possible attacks that must be
* thwarted.
*
* @serial exclude
*/
static class CheckedEntrySet<K,V> implements Set<Map.Entry<K,V>> {
Set<Map.Entry<K,V>> s;
Class<V> valueType;
CheckedEntrySet(Set<Map.Entry<K, V>> s, Class<V> valueType) {
this.s = s;
this.valueType = valueType;
}
public int size() { return s.size(); }
public boolean isEmpty() { return s.isEmpty(); }
public String toString() { return s.toString(); }
public int hashCode() { return s.hashCode(); }
public boolean remove(Object o) { return s.remove(o); }
public boolean removeAll(Collection<?> coll) {
return s.removeAll(coll);
}
public boolean retainAll(Collection<?> coll) {
return s.retainAll(coll);
}
public void clear() {
s.clear();
}
public boolean add(Map.Entry<K, V> e){
throw new UnsupportedOperationException();
}
public boolean addAll(Collection<? extends Map.Entry<K, V>> coll) {
throw new UnsupportedOperationException();
}
public Iterator<Map.Entry<K,V>> iterator() {
return new Iterator<Map.Entry<K,V>>() {
Iterator<Map.Entry<K, V>> i = s.iterator();
public boolean hasNext() { return i.hasNext(); }
public void remove() { i.remove(); }
public Map.Entry<K,V> next() {
return new CheckedEntry<K,V>(i.next(), valueType);
}
};
}
public Object[] toArray() {
Object[] source = s.toArray();
/*
* Ensure that we don't get an ArrayStoreException even if
* s.toArray returns an array of something other than Object
*/
Object[] dest = (CheckedEntry.class.isInstance(
source.getClass().getComponentType()) ? source :
new Object[source.length]);
for (int i = 0; i < source.length; i++)
dest[i] = new CheckedEntry<K,V>((Map.Entry<K,V>)source[i],
valueType);
return dest;
}
public <T> T[] toArray(T[] a) {
// We don't pass a to s.toArray, to avoid window of
// vulnerability wherein an unscrupulous multithreaded client
// could get his hands on raw (unwrapped) Entries from s.
Object[] arr = s.toArray(a.length==0 ? a : Arrays.copyOf(a, 0));
for (int i=0; i<arr.length; i++)
arr[i] = new CheckedEntry<K,V>((Map.Entry<K,V>)arr[i],
valueType);
if (arr.length > a.length)
return (T[])arr;
System.arraycopy(arr, 0, a, 0, arr.length);
if (a.length > arr.length)
a[arr.length] = null;
return a;
}
/**
* This method is overridden to protect the backing set against
* an object with a nefarious equals function that senses
* that the equality-candidate is Map.Entry and calls its
* setValue method.
*/
public boolean contains(Object o) {
if (!(o instanceof Map.Entry))
return false;
return s.contains(
new CheckedEntry<K,V>((Map.Entry<K,V>) o, valueType));
}
/**
* The next two methods are overridden to protect against
* an unscrupulous collection whose contains(Object o) method
* senses when o is a Map.Entry, and calls o.setValue.
*/
public boolean containsAll(Collection<?> coll) {
Iterator<?> e = coll.iterator();
while (e.hasNext())
if (!contains(e.next())) // Invokes safe contains() above
return false;
return true;
}
public boolean equals(Object o) {
if (o == this)
return true;
if (!(o instanceof Set))
return false;
Set<?> that = (Set<?>) o;
if (that.size() != s.size())
return false;
return containsAll(that); // Invokes safe containsAll() above
}
/**
* This "wrapper class" serves two purposes: it prevents
* the client from modifying the backing Map, by short-circuiting
* the setValue method, and it protects the backing Map against
* an ill-behaved Map.Entry that attempts to modify another
* Map Entry when asked to perform an equality check.
*/
private static class CheckedEntry<K,V> implements Map.Entry<K,V> {
private Map.Entry<K, V> e;
private Class<V> valueType;
CheckedEntry(Map.Entry<K, V> e, Class<V> valueType) {
this.e = e;
this.valueType = valueType;
}
public K getKey() { return e.getKey(); }
public V getValue() { return e.getValue(); }
public int hashCode() { return e.hashCode(); }
public String toString() { return e.toString(); }
public V setValue(V value) {
if (!valueType.isInstance(value))
throw new ClassCastException("Attempt to insert " +
value.getClass() +
" value into collection with value type " + valueType);
return e.setValue(value);
}
public boolean equals(Object o) {
if (!(o instanceof Map.Entry))
return false;
Map.Entry t = (Map.Entry)o;
return eq(e.getKey(), t.getKey()) &&
eq(e.getValue(), t.getValue());
}
}
}
}
/**
* 返回一个类型安全的集合SortedMap
*/
public static <K,V> SortedMap<K,V> checkedSortedMap(SortedMap<K, V> m,
Class<K> keyType,
Class<V> valueType) {
return new CheckedSortedMap<K,V>(m, keyType, valueType);
}
/**
* @serial include
*/
static class CheckedSortedMap<K,V> extends CheckedMap<K,V>
implements SortedMap<K,V>, Serializable
{
private static final long serialVersionUID = 1599671320688067438L;
private final SortedMap<K, V> sm;
CheckedSortedMap(SortedMap<K, V> m,
Class<K> keyType, Class<V> valueType) {
super(m, keyType, valueType);
sm = m;
}
public Comparator<? super K> comparator() { return sm.comparator(); }
public K firstKey() { return sm.firstKey(); }
public K lastKey() { return sm.lastKey(); }
public SortedMap<K,V> subMap(K fromKey, K toKey) {
return new CheckedSortedMap<K,V>(sm.subMap(fromKey, toKey),
keyType, valueType);
}
public SortedMap<K,V> headMap(K toKey) {
return new CheckedSortedMap<K,V>(sm.headMap(toKey),
keyType, valueType);
}
public SortedMap<K,V> tailMap(K fromKey) {
return new CheckedSortedMap<K,V>(sm.tailMap(fromKey),
keyType, valueType);
}
}
// 其他
/**
* 不可变的空集
*/
public static final Set EMPTY_SET = new EmptySet();
/**
*
* 返回一个不可变的空集
* size始终为0
*/
public static final <T> Set<T> emptySet() {
return (Set<T>) EMPTY_SET;
}
/**
* @serial include
*/
private static class EmptySet extends AbstractSet<Object> implements Serializable {
// use serialVersionUID from JDK 1.2.2 for interoperability
private static final long serialVersionUID = 1582296315990362920L;
public Iterator<Object> iterator() {
return new Iterator<Object>() {
public boolean hasNext() {
return false;
}
public Object next() {
throw new NoSuchElementException();
}
public void remove() {
throw new UnsupportedOperationException();
}
};
}
public int size() {return 0;}
public boolean contains(Object obj) {return false;}
// Preserves singleton property
private Object readResolve() {
return EMPTY_SET;
}
}
public static final List EMPTY_LIST = new EmptyList();
public static final <T> List<T> emptyList() {
return (List<T>) EMPTY_LIST;
}
/**
* @serial include
*/
private static class EmptyList extends AbstractList<Object>
implements RandomAccess, Serializable {
// use serialVersionUID from JDK 1.2.2 for interoperability
private static final long serialVersionUID = 8842843931221139166L;
public int size() {return 0;}
public boolean contains(Object obj) {return false;}
public Object get(int index) {
throw new IndexOutOfBoundsException("Index: "+index);
}
// Preserves singleton property
private Object readResolve() {
return EMPTY_LIST;
}
}
public static final Map EMPTY_MAP = new EmptyMap();
public static final <K,V> Map<K,V> emptyMap() {
return (Map<K,V>) EMPTY_MAP;
}
private static class EmptyMap
extends AbstractMap<Object,Object>
implements Serializable {
private static final long serialVersionUID = 6428348081105594320L;
public int size() {return 0;}
public boolean isEmpty() {return true;}
public boolean containsKey(Object key) {return false;}
public boolean containsValue(Object value) {return false;}
public Object get(Object key) {return null;}
public Set<Object> keySet() {return Collections.<Object>emptySet();}
public Collection<Object> values() {return Collections.<Object>emptySet();}
public Set<Map.Entry<Object,Object>> entrySet() {
return Collections.emptySet();
}
public boolean equals(Object o) {
return (o instanceof Map) && ((Map)o).size()==0;
}
public int hashCode() {return 0;}
// Preserves singleton property
private Object readResolve() {
return EMPTY_MAP;
}
}
/**
*
* 返回只包含一个元素的不可变的集合
*/
public static <T> Set<T> singleton(T o) {
return new SingletonSet<T>(o);
}
/**
* @serial include
*/
private static class SingletonSet<E> extends AbstractSet<E>
implements Serializable{
// use serialVersionUID from JDK 1.2.2 for interoperability
private static final long serialVersionUID = 3193687207550431679L;
final private E element;
SingletonSet(E e) {element = e;}
public Iterator<E> iterator() {
return new Iterator<E>() {
private boolean hasNext = true;
public boolean hasNext() {
return hasNext;
}
public E next() {
if (hasNext) {
hasNext = false;
return element;
}
throw new NoSuchElementException();
}
public void remove() {
throw new UnsupportedOperationException();
}
};
}
public int size() {return 1;}
public boolean contains(Object o) {return eq(o, element);}
}
public static <T> List<T> singletonList(T o) {
return new SingletonList<T>(o);
}
private static class SingletonList<E>
extends AbstractList<E>
implements RandomAccess, Serializable {
static final long serialVersionUID = 3093736618740652951L;
private final E element;
SingletonList(E obj) {element = obj;}
public int size() {return 1;}
public boolean contains(Object obj) {return eq(obj, element);}
public E get(int index) {
if (index != 0)
throw new IndexOutOfBoundsException("Index: "+index+", Size: 1");
return element;
}
}
public static <K,V> Map<K,V> singletonMap(K key, V value) {
return new SingletonMap<K,V>(key, value);
}
private static class SingletonMap<K,V> extends AbstractMap<K,V>
implements Serializable {
private static final long serialVersionUID = -6979724477215052911L;
private final K k;
private final V v;
SingletonMap(K key, V value) {
k = key;
v = value;
}
public int size() {return 1;}
public boolean isEmpty() {return false;}
public boolean containsKey(Object key) {return eq(key, k);}
public boolean containsValue(Object value) {return eq(value, v);}
public V get(Object key) {return (eq(key, k) ? v : null);}
private transient Set<K> keySet = null;
private transient Set<Map.Entry<K,V>> entrySet = null;
private transient Collection<V> values = null;
public Set<K> keySet() {
if (keySet==null)
keySet = singleton(k);
return keySet;
}
public Set<Map.Entry<K,V>> entrySet() {
if (entrySet==null)
entrySet = Collections.<Map.Entry<K,V>>singleton(
new SimpleImmutableEntry<K,V>(k, v));
return entrySet;
}
public Collection<V> values() {
if (values==null)
values = singleton(v);
return values;
}
}
/**
*
* 返回一个包含N个o元素的比可变的集合
* @param n 添加的指定元素的个数
* @param o 被重复添加的元素
*/
public static <T> List<T> nCopies(int n, T o) {
if (n < 0)
throw new IllegalArgumentException("List length = " + n);
return new CopiesList<T>(n, o);
}
/**
* @serial include
*/
private static class CopiesList<E>extends AbstractList<E>
implements RandomAccess, Serializable{
static final long serialVersionUID = 2739099268398711800L;
final int n;
final E element;
CopiesList(int n, E e) {
assert n >= 0;
this.n = n;
element = e;
}
public int size() {
return n;
}
public boolean contains(Object obj) {
return n != 0 && eq(obj, element);
}
public int indexOf(Object o) {
return contains(o) ? 0 : -1;
}
public int lastIndexOf(Object o) {
return contains(o) ? n - 1 : -1;
}
public E get(int index) {
if (index < 0 || index >= n)
throw new IndexOutOfBoundsException("Index: "+index+
", Size: "+n);
return element;
}
public Object[] toArray() {
final Object[] a = new Object[n];
if (element != null)
Arrays.fill(a, 0, n, element);
return a;
}
public <T> T[] toArray(T[] a) {
final int n = this.n;
if (a.length < n) {
a = (T[])java.lang.reflect.Array
.newInstance(a.getClass().getComponentType(), n);
if (element != null)
Arrays.fill(a, 0, n, element);
} else {
Arrays.fill(a, 0, n, element);
if (a.length > n)
a[n] = null;
}
return a;
}
public List<E> subList(int fromIndex, int toIndex) {
if (fromIndex < 0)
throw new IndexOutOfBoundsException("fromIndex = " + fromIndex);
if (toIndex > n)
throw new IndexOutOfBoundsException("toIndex = " + toIndex);
if (fromIndex > toIndex)
throw new IllegalArgumentException("fromIndex(" + fromIndex +
") > toIndex(" + toIndex + ")");
return new CopiesList(toIndex - fromIndex, element);
}
}
/**
* 返回一个比较器，该比较器能使集合按降序排列
* 例如：
* Arrays.sort(a, Collections.reverseOrder());
* 能按字母表相反的顺序排列数组
*
*/
public static <T> Comparator<T> reverseOrder() {
return (Comparator<T>) REVERSE_ORDER;
}
private static final Comparator REVERSE_ORDER = new ReverseComparator();
/**
* @serial include
*/
private static class ReverseComparator<T>
implements Comparator<Comparable<Object>>, Serializable {
// use serialVersionUID from JDK 1.2.2 for interoperability
private static final long serialVersionUID = 7207038068494060240L;
public int compare(Comparable<Object> c1, Comparable<Object> c2) {
return c2.compareTo(c1);
}
private Object readResolve() { return reverseOrder(); }
}
/**
* 根据指定比较器的相反顺序排列集合
*/
public static <T> Comparator<T> reverseOrder(Comparator<T> cmp) {
if (cmp == null)
return reverseOrder();
return new ReverseComparator2<T>(cmp);
}
/**
* @serial include
*/
private static class ReverseComparator2<T> implements Comparator<T>,
Serializable{
private static final long serialVersionUID = 4374092139857L;
private Comparator<T> cmp;
ReverseComparator2(Comparator<T> cmp) {
assert cmp != null;
this.cmp = cmp;
}
public int compare(T t1, T t2) {
return cmp.compare(t2, t1);
}
}
/**
* 基于c之上返回一个枚举集
*/
public static <T> Enumeration<T> enumeration(final Collection<T> c) {
return new Enumeration<T>() {
Iterator<T> i = c.iterator();
public boolean hasMoreElements() {
return i.hasNext();
}
public T nextElement() {
return i.next();
}
};
}
/**
* 根据枚举集中的元素返回一个ArrayList
*/
public static <T> ArrayList<T> list(Enumeration<T> e) {
ArrayList<T> l = new ArrayList<T>();
while (e.hasMoreElements())
l.add(e.nextElement());
return l;
}
/**
* 判断两对象是否相等或同位空
*/
private static boolean eq(Object o1, Object o2) {
return (o1==null ? o2==null : o1.equals(o2));
}
/**
* 返回c中与o相等的元素的个数
*/
public static int frequency(Collection<?> c, Object o) {
int result = 0;
if (o == null) {
for (Object e : c)
if (e == null)
result++;
} else {
for (Object e : c)
if (o.equals(e))
result++;
}
return result;
}
/**
*
* 如果两指定集合没有共同的元素则返回true
*/
public static boolean disjoint(Collection<?> c1, Collection<?> c2) {
/*
*
* 优先遍历的始终是size小的集合或非Set的集合
*/
if ((c1 instanceof Set) && !(c2 instanceof Set) ||
(c1.size() > c2.size())) {
Collection<?> tmp = c1;
c1 = c2;
c2 = tmp;
}
for (Object e : c1)
if (c2.contains(e))
return false;
return true;
}
/**
* 把所有指定元素添加到集合c中，
* 有一个元素添加成功就返回true
*/
public static <T> boolean addAll(Collection<? super T> c, T... elements) {
boolean result = false;
for (T element : elements)
result |= c.add(element);
return result;
}
/**
* 根据指定的map返回一个set
* set存储的是map的键值
*/
public static <E> Set<E> newSetFromMap(Map<E, Boolean> map) {
return new SetFromMap<E>(map);
}
private static class SetFromMap<E> extends AbstractSet<E>
implements Set<E>, Serializable
{
private final Map<E, Boolean> m; // The backing map
private transient Set<E> s; // Its keySet
SetFromMap(Map<E, Boolean> map) {
if (!map.isEmpty())
throw new IllegalArgumentException("Map is non-empty");
m = map;
s = map.keySet();
}
public void clear() { m.clear(); }
public int size() { return m.size(); }
public boolean isEmpty() { return m.isEmpty(); }
public boolean contains(Object o) { return m.containsKey(o); }
public boolean remove(Object o) { return m.remove(o) != null; }
public boolean add(E e) { return m.put(e, Boolean.TRUE) == null; }
public Iterator<E> iterator() { return s.iterator(); }
public Object[] toArray() { return s.toArray(); }
public <T> T[] toArray(T[] a) { return s.toArray(a); }
public String toString() { return s.toString(); }
public int hashCode() { return s.hashCode(); }
public boolean equals(Object o) { return o == this || s.equals(o); }
public boolean containsAll(Collection<?> c) {return s.containsAll(c);}
public boolean removeAll(Collection<?> c) {return s.removeAll(c);}
public boolean retainAll(Collection<?> c) {return s.retainAll(c);}
// addAll is the only inherited implementation
private static final long serialVersionUID = 2454657854757543876L;
private void readObject(java.io.ObjectInputStream stream)
throws IOException, ClassNotFoundException
{
stream.defaultReadObject();
s = m.keySet();
}
}
/**
*
* 把指定Deque包装成一个后进先出的队列
* add方法对应push，remove方法对应pop等。
*
*/
public static <T> Queue<T> asLifoQueue(Deque<T> deque) {
return new AsLIFOQueue<T>(deque);
}
static class AsLIFOQueue<E> extends AbstractQueue<E>
implements Queue<E>, Serializable {
private static final long serialVersionUID = 1802017725587941708L;
private final Deque<E> q;
AsLIFOQueue(Deque<E> q) { this.q = q; }
public boolean add(E e) { q.addFirst(e); return true; }
public boolean offer(E e) { return q.offerFirst(e); }
public E poll() { return q.pollFirst(); }
public E remove() { return q.removeFirst(); }
public E peek() { return q.peekFirst(); }
public E element() { return q.getFirst(); }
public void clear() { q.clear(); }
public int size() { return q.size(); }
public boolean isEmpty() { return q.isEmpty(); }
public boolean contains(Object o) { return q.contains(o); }
public boolean remove(Object o) { return q.remove(o); }
public Iterator<E> iterator() { return q.iterator(); }
public Object[] toArray() { return q.toArray(); }
public <T> T[] toArray(T[] a) { return q.toArray(a); }
public String toString() { return q.toString(); }
public boolean containsAll(Collection<?> c) {return q.containsAll(c);}
public boolean removeAll(Collection<?> c) {return q.removeAll(c);}
public boolean retainAll(Collection<?> c) {return q.retainAll(c);}
// We use inherited addAll; forwarding addAll would be wrong
}
}