Java Comparable和Comparator的用法与区别

一、场景介绍

java中给了我们两个接口Comparable和Comparator，对自己定义的数据结构需要进行指定排序。

comparable接口定义一个方法:

 public interface Comparable<T> {
    public int compareTo(T o);
 }

comparator接口定义方法（有些类实现了comparator，但是没有实现equals方式是因为Object类已经实现了equals方法）：

public interface Comparator<T> {
    int compare(T o1, T o2);
    boolean equals(Object obj);
}

comparable接口和Comparator接口 主要区别

• 1、实现了comparable的对象直接就可以成为一个可以比较的对象，不过得在类中进行方法定义。
• 2、comparator在对象外比较，不修改实体类。

二、两个接口用法介绍

public class Student implements Comparable<Student> {

    private String name;

    private int age;

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

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

    public Student(String name, int age) {
        super();
        this.name = name;
        this.age = age;
    }

    public Student() {
       super();
        	
    }

    @Override
    public int compareTo(Student o) {
        if(this.age == o.getAge() &&this.name == o.getName()){
            return 0;
        }else if(this.age > o.getAge()){
            return 1;
        }else{
            return -1;
        }
    }
    
    @Override
    public String toString() {
        return "Student[name="+this.name+",age="+this.age+"]";
    }
}

main方法测试

public static void main(String[] args) {
        
        List<Student> list = new ArrayList<Student>();
        list.add(new Student("Hello1",32));
        list.add(new Student("Hello2",100));
        list.add(new Student("Hello3",19));
        list.add(new Student("Hello4",34));
        
        System.out.println("===================未排序结果========================");
 
        for (Student student : list) {
            System.out.println(student.toString());
        }
        
        System.out.println("===============Comparable接口排序结果=================");
        
        Collections.sort(list);
        for (Student student : list) {
            System.out.println(student.toString());
        }
        
        
        System.out.println("===============Comparator接口排序结果=================");
        Collections.sort(list, new Comparator<Student>() {
            @Override
            public int compare(Student o1, Student o2) {
                if(o1.age == o1.getAge() &&o1.name == o2.getName()){
                    return 0;
                }else if(o1.age < o2.age){
                    return 1;
                }else{
                    return -1;
                }
            }
        });
        
        for (Student student : list) {
            System.out.println(student.toString());
        }
        
        System.out.println("===============lambda表达式排序结果===================");
        
        Collections.sort(list,(o1,o2)->(o1.getAge()-o2.getAge()));
        list.forEach(student->{
            System.out.println(student.toString());
        });
        

    }

执行结果

===================未排序结果========================
Student[name=Hello1,age=32]
Student[name=Hello2,age=100]
Student[name=Hello3,age=19]
Student[name=Hello4,age=34]
===============Comparable接口排序结果=================
Student[name=Hello3,age=19]
Student[name=Hello1,age=32]
Student[name=Hello4,age=34]
Student[name=Hello2,age=100]
===============Comparator接口排序结果=================
Student[name=Hello2,age=100]
Student[name=Hello4,age=34]
Student[name=Hello1,age=32]
Student[name=Hello3,age=19]
===============lambda表达式排序结果===================
Student[name=Hello3,age=19]
Student[name=Hello1,age=32]
Student[name=Hello4,age=34]
Student[name=Hello2,age=100]