首先,先看代码内容:(希望大家自己可以运行尝试,以加深记忆和理解)
package s11; import java.util.Comparator; import java.util.TreeSet; class Student implements Comparable { String name; int age; int classNum; public Student() { } public Student(String name, int age, int classNum) { this.name = name; this.age = age; this.classNum = classNum; } public String toString() { return "Student [name=" + name + ", age=" + age + ", classNum=" + classNum + "]"; } public int compareTo(Object o) { Student s = (Student) o; return this.classNum - s.classNum; } } public class Studentdemo { public static void main(String[] args) { TreeSet ts1 = new TreeSet( new Comparator() { public int compare(Object o1,Object o2) { Student s1 = (Student)o1; Student s2 = (Student)o2; return s1.age > s2.age ? 1 : -1; } }); ts1.add(new Student("mm",21,97005)); ts1.add(new Student("jerry",19,97003)); ts1.add(new Student("tom",16,97004)); ts1.add(new Student("mm",28,97008)); ts1.add(new Student("mm",23,97006)); System.out.println("语句return s1.age > s2.age ? 1 : -1;是按照???排列的:"); System.out.println(ts1); } }
这是运行结果:
语句return s1.age > s2.age ? 1 : -1;是按照升序(由小到大)排列的:
[Student [name=tom, age=16, classNum=97004],
Student [name=jerry, age=19, classNum=97003],
Student [name=mm, age=21, classNum=97005],
Student [name=mm, age=23, classNum=97006],
Student [name=mm, age=28, classNum=97008]]
也就是说当语句return s1.age > s2.age ? 1 : -1;的返回值为1时,也就是说 s1的值大于s2的值时 ,compareTo是按照升序(由小到大)排序的!
当返回值为-1时,也就是说 s1的值小于s2的值时 ,compareTo是按照降序(由大到小)排序的!
当返回值为0时,s1等于s2的值,如果数值全部相等则排序也同样按照初始顺序排列,如果只有前两个数值相等,那么,compareTo会继续比较下一组s1 与 s2的值,同样, s1的值大于s2的值时 ,compareTo是按照升序(由小到大)排序的, s1的值小于s2的值时 ,compareTo是按照降序(由大到小)排序的!希望大家今天能彻底明白,不枉辛苦一字,谢谢!