比较器报错：Comparison method violates its general contract

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转载自：http://blog.csdn.net/fanzitao/article/details/8040201

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");

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);}}}

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