Comparable和Comparator的用法与区别

以你之姓@ 2022-05-17 01:15 326阅读 0赞

# 一 应用场景: #

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

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(jdk版本不同数量不同)注意：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);
    }

区别在于: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；comparator在对象外比较，不修改实体类。

# 二  实例演示 #

## 1  Comparable用法 ##

1 定义一个Person实体类实现Comparable接口

public class Person implements Comparable<Person>{
    	public int age;    //年龄
    	public String name;  //姓名
    
        //get、set方法
    	public int getAge() {
    		return age;
    	}
    	public void setAge(int age) {
    		this.age = age;
    	}
    	public String getName() {
    		return name;
    	}
    	public void setName(String name) {
    		this.name = name;
    	}
    	public Person(int age, String name) {
    		super();
    		this.age = age;
    		this.name = name;
    	}
    	@Override
    	public String toString() {
    		return "Person [age=" + age + ", name=" + name + "]";
    	}
        //实现Comparable接口必须实现compareTo方法
    	public  int compareTo(Person o) {
    	    if(this.age==o.age&&this.name==o.name){
    	    	return 0;
    	    }else if(this.age>o.age){
    	    	System.out.println("this.age:"+this.age+"o.age:"+o.age);
    	    	return 1;
    	    }else{
    	    	return -1;
    	    }	
    		}
    	public Person() {
    		super();
    		// TODO Auto-generated constructor stub
    	}
    	
    
    }

2  编写测试类进行测试（使用Junit）

import org.junit.Test;
    import junit.framework.TestCase;
    public class TestCompare extends TestCase {
        @Test
    	public void test1(){
    		List<Person> list=new ArrayList<Person>();
    		Person test1=new Person(66,"李四");
    		Person test2=new Person(29,"王五");
    		Person test3=new Person(28,"赵六");
    		Person test4=new Person(20,"钱三");
    		list.add(test4);
    		list.add(test3);
    		list.add(test2);
    		list.add(test1);
    		Collections.sort(list);
    		for(Object s:list){
    			System.out.println(s);
    		}
    	}
    }

3 运行结果：对象实现了comparable接口就自动排序

this.age:28o.age:20
    this.age:29o.age:28
    this.age:66o.age:29
    Person [age=20, name=钱三]
    Person [age=28, name=赵六]
    Person [age=29, name=王五]
    Person [age=66, name=李四]

## 2 Comparator用法 ##

1 定义一个实体类

public class emp {
    	public int age;
    	public String name;
    	public int getAge() {
    		return age;
    	}
    	public void setAge(int age) {
    		this.age = age;
    	}
    	public String getName() {
    		return name;
    	}
    	public void setName(String name) {
    		this.name = name;
    	}
    	public emp(int age, String name) {
    		super();
    		this.age = age;
    		this.name = name;
    	}
    	public emp() {
    		super();
    		// TODO Auto-generated constructor stub
    	}
    	@Override
    	public String toString() {
    		return "emp [age=" + age + ", name=" + name + "]";
    	}
    }

2 编写测试类测试:

import org.junit.Test;
    import junit.framework.TestCase;
    public class TestCompare extends TestCase {
         @Test
    	public void test2(){
    		List<emp> list=new ArrayList<emp>();
    		emp test1=new emp(69,"李四");
    		emp test2=new emp(29,"王五");
    		emp test3=new emp(28,"赵六");
    		emp test4=new emp(20,"钱三");
    		list.add(test4);
    		list.add(test3);
    		list.add(test2);
    		list.add(test1);
    		Collections.sort(list,new Comparator<emp>(){
    			@Override
    			public int compare(emp o1, emp o2) {
    				if(o1.age==o2.age&&o1.name==o2.name){
    					return 0;
    				}else if(o1.age>o2.age){
    					return 1;			
    				}else{
    					return 0;
    				}
    			}
    		});		
    		for(Object s:list){
    			System.out.println(s);
    		}		
    	}	
    }

3 运行结果：

emp [age=20, name=钱三]
    emp [age=28, name=赵六]
    emp [age=29, name=王五]
    emp [age=69, name=李四]

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