Brother Zeng遇到的错误:
java.lang.IllegalArgumentException: Comparison method violates its general contract!
网上查到一个解释:
Description: The sorting algorithm used by java.util.Arrays.sort and (indirectly) by java.util.Collections.sort has been replaced. The new sort implementation may throw an IllegalArgumentException if it detects a Comparable that violates the Comparable contract.
The previous implementation silently ignored such a situation. If the previous behavior is desired, you can use the new system property, java.util.Arrays.useLegacyMergeSort, to restore previous mergesort behavior.
也就是说jdk 7的sort函数的实现变了,造成了这个问题,具体原因未知。
改一下系统设置,还是选择使用老版本的排序方法,在代码前面加上这么一句话:System.setProperty("java.util.Arrays.useLegacyMergeSort", "true");
另外复习一下比较器,一个简单的例子:
类代码:
public class Stu { public double age; public String name; public Stu(String name,double age) { this.name = name; this.age = age; } }
主题代码
import java.util.Collections; import java.util.Comparator; import java.util.List; public class CodeForBrotherZeng { /** * @param args */ public static void main(String[] args) { Stu stu1=new Stu("foyd",22.1); Stu stu2=new Stu("teddy",19.1); Stu stu3=new Stu("dean",26.1); Stu stu4=new Stu("lucas",19.1); Stu stu5=new Stu("tina",26.1); List<Stu> list = new ArrayList<Stu>(); list.add(stu1); list.add(stu2); list.add(stu3); list.add(stu4); list.add(stu5); Comparator<Stu> comparator = new Comparator<Stu>() { public int compare(Stu p1, Stu p2) {//return必须是int,而str.age是double,所以不能直接return (p1.age-p2.age) if((p1.age-p2.age)<0) return -1; else if((p1.age-p2.age)>0) return 1; else return 0; } }; //jdk 7sort有可能报错, //加上这句话:System.setProperty("java.util.Arrays.useLegacyMergeSort", "true"); //表示,使用以前版本的sort来排序 Collections.sort(list,comparator); for(int i=0;i<list.size();i++) { System.out.println(list.get(i).age+" "+list.get(i).name); } } }