17.1 完整的容器分类法
17.2 填充容器
这一小节，简单的介绍了java.util.Collections中的两个方法：
public static <T> List<T> nCopies(int n,T o)
public static <T> void fill(List<? super T> list,T obj)
这两个方法可以多次拷贝同一个对象到一个列表中
java代码：
//The Collections.fill() & Collections.nCopies() methods.
package containers;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
class StringAddress {
private String s;
public StringAddress(String s) {
this.s = s;
}
@Override
public String toString() {
return super.toString() + " " + s;
}
}
public class FillingLists {
public static void main(String[] args) {
List<StringAddress> list = new ArrayList<StringAddress>(
Collections.nCopies(4, new StringAddress("Hello")));
System.out.println(list);
Collections.fill(list, new StringAddress("World"));
System.out.println(list);
}
}
运行结果：
[containers.StringAddress@4e81d783 Hello, containers.StringAddress@4e81d783 Hello, containers.StringAddress@4e81d783 Hello, containers.StringAddress@4e81d783 Hello] [containers.StringAddress@2e6c01b9 World, containers.StringAddress@2e6c01b9 World, containers.StringAddress@2e6c01b9 World, containers.StringAddress@2e6c01b9 World]
A Generator solution
package net.mindview.util;
import java.util.ArrayList;
/**
* 该类本身就是一个ArrayList，把Generator生成器生成的对象添加到该类中
* list方法返回一个CollectionData对象
*/
public class CollectionData<T> extends ArrayList<T> {
public CollectionData(Generator<T> gen, int quantity) {
for (int i = 0; i < quantity; i++) {
add(gen.next());
}
}
// A generic convenience method:
public static <T> CollectionData<T> list(Generator<T> gen, int quantity) {
return new CollectionData<T>(gen, quantity);
}
}
把生成器对象转换称Collection
测试代码：
package containers;
import java.util.LinkedHashSet;
import java.util.Set;
import net.mindview.util.CollectionData;
import net.mindview.util.Generator;
class Government implements Generator<String>{
String[] foundation = ("strange women lying in ponds " +
"distributing swords is no basis for a system of " +
"government").split(" ");
private int index;
@Override
public String next() {
return foundation[index++];
}
}
public class CollectionDataTest {
public static void main(String[] args) {
Set<String> set = new LinkedHashSet<>(
new CollectionData<>(new Government(), 15));
//Using the convenience method
set.addAll(CollectionData.list(new Government(), 15));
System.out.println(set);
}
}
package containers;
import java.util.ArrayList;
import java.util.HashSet;
import net.mindview.util.CollectionData;
import net.mindview.util.RandomGenerator;
public class CollectionDataGeneration {
public static void main(String[] args) {
System.out.println(new ArrayList<String>(
CollectionData.list(//Convenience method
new RandomGenerator.String(9),10)));
System.out.println(new HashSet<Integer>(
new CollectionData<Integer>(
new RandomGenerator.Integer(),10)));
}
}
在实验的过程中需要用的其他类：
//: net/mindview/util/Generator.java
// A generic interface.
package net.mindview.util;
public interface Generator<T> { T next(); } ///:~
//: net/mindview/util/CountingGenerator.java
// Simple generator implementations.
package net.mindview.util;
public class CountingGenerator {
public static class
Boolean implements Generator<java.lang.Boolean> {
private boolean value = false;
public java.lang.Boolean next() {
value = !value; // Just flips back and forth
return value;
}
}
public static class
Byte implements Generator<java.lang.Byte> {
private byte value = 0;
public java.lang.Byte next() { return value++; }
}
static char[] chars = ("abcdefghijklmnopqrstuvwxyz" +
"ABCDEFGHIJKLMNOPQRSTUVWXYZ").toCharArray();
public static class
Character implements Generator<java.lang.Character> {
int index = -1;
public java.lang.Character next() {
index = (index + 1) % chars.length;
return chars[index];
}
}
public static class
String implements Generator<java.lang.String> {
private int length = 7;
Generator<java.lang.Character> cg = new Character();
public String() {}
public String(int length) { this.length = length; }
public java.lang.String next() {
char[] buf = new char[length];
for(int i = 0; i < length; i++)
buf[i] = cg.next();
return new java.lang.String(buf);
}
}
public static class
Short implements Generator<java.lang.Short> {
private short value = 0;
public java.lang.Short next() { return value++; }
}
public static class
Integer implements Generator<java.lang.Integer> {
private int value = 0;
public java.lang.Integer next() { return value++; }
}
public static class
Long implements Generator<java.lang.Long> {
private long value = 0;
public java.lang.Long next() { return value++; }
}
public static class
Float implements Generator<java.lang.Float> {
private float value = 0;
public java.lang.Float next() {
float result = value;
value += 1.0;
return result;
}
}
public static class
Double implements Generator<java.lang.Double> {
private double value = 0.0;
public java.lang.Double next() {
double result = value;
value += 1.0;
return result;
}
}
} ///:~
//: net/mindview/util/RandomGenerator.java
// Generators that produce random values.
package net.mindview.util;
import java.util.*;
public class RandomGenerator {
private static Random r = new Random(47);
public static class
Boolean implements Generator<java.lang.Boolean> {
public java.lang.Boolean next() {
return r.nextBoolean();
}
}
public static class
Byte implements Generator<java.lang.Byte> {
public java.lang.Byte next() {
return (byte)r.nextInt();
}
}
public static class
Character implements Generator<java.lang.Character> {
public java.lang.Character next() {
return CountingGenerator.chars[
r.nextInt(CountingGenerator.chars.length)];
}
}
public static class
String extends CountingGenerator.String {
// Plug in the random Character generator:
{ cg = new Character(); } // Instance initializer
public String() {}
public String(int length) { super(length); }
}
public static class
Short implements Generator<java.lang.Short> {
public java.lang.Short next() {
return (short)r.nextInt();
}
}
public static class
Integer implements Generator<java.lang.Integer> {
private int mod = 10000;
public Integer() {}
public Integer(int modulo) { mod = modulo; }
public java.lang.Integer next() {
return r.nextInt(mod);
}
}
public static class
Long implements Generator<java.lang.Long> {
private int mod = 10000;
public Long() {}
public Long(int modulo) { mod = modulo; }
public java.lang.Long next() {
return new java.lang.Long(r.nextInt(mod));
}
}
public static class
Float implements Generator<java.lang.Float> {
public java.lang.Float next() {
// Trim all but the first two decimal places:
int trimmed = Math.round(r.nextFloat() * 100);
return ((float)trimmed) / 100;
}
}
public static class
Double implements Generator<java.lang.Double> {
public java.lang.Double next() {
long trimmed = Math.round(r.nextDouble() * 100);
return ((double)trimmed) / 100;
}
}
} ///:~