JDK7抛出异常:Comparison method violates its ……（急求解决，附赠答案奖励）

Question

最近在学Java，后续尝试用Java在云服务器上做个项目，手里的服务器是借助阿里云免费套餐活动开通的，先定一个小目标。 不过在做一个年龄排序题目的时候，JDK7版本运行抛出异常：Comparison method violates its general contract。 下面是代码： import java.util.Arrays; import java.util.Collections; import java.util.Comparator; import java.util.List; public class SortTest { static class Student { //姓名 String name; //年龄 int age; //性别 String sex; public Student(String name, int age, String sex) { super(); this.name = name; this.age = age; this.sex = sex; } /** * @return the name */ public String getName() { return name; } /** * @return the age */ public int getAge() { return age; } /** * @return the sex */ public String getSex() { return sex; } @Override public String toString() { return "name:" + name + ",age:" + age + ",sex:" + sex; } } /** * @param args */ public static void main(String[] args) { System.setProperty("java.util.Arrays.useLegacyMergeSort", "false"); Student stu1 = new Student("张三", 11, "男"); Student stu2 = new Student("李四", 12, "男"); Student stu3 = new Student("王五", 13, "女"); Student stu4 = new Student("刘六", 12, "女"); Student stu5 = new Student("张三", 11, "男"); Student stu14 = new Student("张三", 11, "男"); Student stu6 = new Student("张三", 11, "男"); Student stu7 = new Student("张三", 11, "男"); Student stu8 = new Student("张三", 11, "男"); Student stu9 = new Student("张三", 12, "男"); Student stu10 = new Student("张三", 11, "男"); Student stu11 = new Student("张三", 11, "男"); Student stu12 = new Student("张三", 15, "男"); Student stu13 = new Student("张三", 11, "男"); List<Student> stuList = Arrays.asList(stu1, stu2, stu3, stu4, stu5, stu6, stu7, stu8, stu9, stu10, stu11, stu12, stu13, stu14, stu5, stu1, stu2, stu3, stu4, stu1, stu2, stu3, stu4, stu5, stu6, stu7, stu8, stu9, stu10, stu11, stu12, stu13, stu14, stu5, stu1, stu2, stu3, stu4, stu1, stu2, stu3, stu4, stu5, stu6, stu7, stu8, stu9, stu10, stu11, stu12, stu13, stu14, stu5, stu1, stu2, stu3, stu4, stu1, stu2, stu3, stu4, stu5, stu6, stu7, stu8, stu9, stu10, stu11, stu12, stu13, stu14, stu5, stu1, stu2, stu3, stu4, stu1, stu2, stu3, stu4, stu5, stu6, stu7, stu8, stu9, stu10, stu11, stu12, stu13, stu14, stu5, stu1, stu2, stu3, stu4); Collections.sort(stuList, new Comparator<Student>() { @Override public int compare(Student o1, Student o2) { return o1.getAge() > o2.getAge() ? 1 : (o1.getAge() == o2.getAge() ? 0 : -1); } }); for (Student student : stuList) { System.out.println(student); } List<Integer> list = Arrays.asList(2, 1, 1, 3, 2); Collections.sort(list, new Comparator<Integer>() { @Override public int compare(Integer o1, Integer o2) { return o1 > o2 ? 1 : -1; } }); } } 急求解答！附赠阿里云免费套餐邀请码一个，能开云服务器数据库，很着急谢谢各位了。

Answer 1

这个应该是JDK 个别版本引起的
你可以尝试下：
1>
System.setProperty("java.util.Arrays.useLegacyMergeSort", "true");
2>
public int compare(Integer o1, Integer o2) {

return o1.compareTo(o2);

}

Answer 2

在JDK7版本以上，Comparator要满足自反性，传递性，对称性。所以你需将源代码中的部分：

Collections.sort(list, new Comparator<Integer>() {

        @Override
        public int compare(Integer o1, Integer o2) {
            return o1 > o2 ? 1 : -1;
        }

改成：

Collections.sort(list, new Comparator<Integer>() {

        @Override
        public int compare(Integer o1, Integer o2) {
            return o1 > o2 ? 1 : (o1 == o2 ? 0 : -1);
        }

Answer 3

我用JDK1.7，1.8都运行过，没有报错；

 public int compare(Student o1, Student o2) {
                return o1.getAge() > o2.getAge() ? 1 : (o1.getAge() == o2.getAge() ? 0 : -1);
            }

public int compare(Integer o1, Integer o2) {
                return o1 > o2 ? 1 : -1;
            }

这两个地方是有问题的，JDK无法判断o1.getAge()，o2.getAge()相等的情况。
而且代码也不是这么写，应该是直接
return o1.getAge()-o2.getAge()
return o1-o2