java中的类实现comparable接口 用于排序

import java.util.Arrays;

public class SortApp {
public static void main(String[] args) {
Student[] stus = new Student[3];
stus[0] = new Student(11, 99);
stus[1] = new Student(13, 92);
stus[2] = new Student(13, 89);
Arrays.sort(stus);
for (Student student : stus) {
System.out.println("age=" + student.getAge() + ";" + "score="
+ student.getScore());
}
}

static class Student implements Comparable<Student> {
private int age;
private int score;

public Student() {
}

public Student(int age, int score) {
this.age = age;
this.score = score;
}

public int getScore() {
return score;
}

public void setScore(int score) {
this.score = score;
}

public int getAge() {
return age;
}

public void setAge(int age) {
this.age = age;
}

public int compareTo(Student o) {
int result = this.age - o.age;// o 表示待要比较的对象 result为正 将升序排列 为负将降序排序
if (result != 0) {
return result;
} else {
return this.score - o.score;//如果result=0 将比较第二列
}
}

}
}

上面的例子我们在hadoop中主要是将一行作为一个key进行排序，因为hadoop默认的排序只针对key，value不排序，如要对value排序，我们需要自定义排序规则，将keyvalue同时作为key进行