如何实现对象的排序Comparable

作者：叁念

问题情形：

有这么一组对象（员工类），他们都有姓名属性（name）,工资（salary ）.现在我们希望他能够以工资的多少进行升序排序，应该怎么办？

首先请看员工类组成：

public class User {
private String name;
private double salary;

public User(String name, double salary) {
super();
this.name = name;
this.salary = salary;
}

@Override
public String toString() {
return "User [name=" + name + ", salary=" + salary + "]";
}

}

我们现在有主类如下：

import java.util.Arrays;
import java.util.Random;

public class Test {
public static void main(String[] args) {

User [] userArrary = new User [10];
Random random = new Random();

for (int i = 0; i < userArrary.length; i++) {
int salary = random.nextInt(101);
userArrary[i] = new User("员工" + i + "号", salary);
}
System.out.println(Arrays.toString(userArrary));
}
}

以上输出结果如下：

[User [name=员工0号, salary=69.0],
User [name=员工1号, salary=61.0],
User [name=员工2号, salary=38.0],
User [name=员工3号, salary=19.0],
User [name=员工4号, salary=84.0],
User [name=员工5号, salary=6.0],
User [name=员工6号, salary=7.0],
User [name=员工7号, salary=0.0],
User [name=员工8号, salary=35.0],
User [name=员工9号, salary=36.0]]

好！现在就开始对员工对象以薪水排序，要实现Comparable接口，重写compareTo方法

public class User implements Comparable<User> {
private String name;
private double salary;

public User(String name, double salary) {
super();
this.name = name;
this.salary = salary;
}

@Override
public String toString() {
return "User [name=" + name + ", salary=" + salary + "]";
}

@Override
public int compareTo(User o) {
if(this.salary > o.salary) return 1;
else if(this.salary < o.salary) return -1;
else return 0;

//      也可以这么写
//      return Double.compare(this.salary, o.salary);

}

}

4.主类写法以及运行结果（这样就实现了以对象属性大小的排序）

import java.util.Arrays;
import java.util.Random;

public class Test {
public static void main(String[] args) {

User [] userArrary = new User [10];
Random random = new Random();

for (int i = 0; i < userArrary.length; i++) {
int salary = random.nextInt(101);
userArrary[i] = new User("员工" + i + "号", salary);
}
System.out.println(Arrays.toString(userArrary));

System.out.println("排序后：");
//      排序
Arrays.sort(userArrary);
System.out.println(Arrays.toString(userArrary));
}
}

结果：

[User [name=员工0号, salary=42.0],
User [name=员工1号, salary=66.0],
User [name=员工3号, salary=2.0],
User [name=员工5号, salary=0.0],
User [name=员工6号, salary=58.0],
User [name=员工7号, salary=70.0],
User [name=员工8号, salary=87.0],
User [name=员工9号, salary=7.0]]
排序后：
[User [name=员工5号, salary=0.0],
User [name=员工3号, salary=2.0],
User [name=员工9号, salary=7.0],
User [name=员工4号, salary=23.0],
User [name=员工0号, salary=42.0],
User [name=员工6号, salary=58.0],
User [name=员工1号, salary=66.0],
User [name=员工7号, salary=70.0],
User [name=员工2号, salary=82.0],
User [name=员工8号, salary=87.0]]