Java Comparable接口以及Comparator类

实现Comparable接口的自然排序

实现类基于compareTo()方法的排序被称为自然排序,在JDK中,如Integer,Double和String等都实现了Comparable接口的,接口中有一个int compartTo(Object o)方法,返回整数类型.

Comparator接口的自定义排序

实现Comparator接口的类会实现一个compare(Object o1, Object o2)的方法,如果类的设计没有考虑到Compare的问题而没有实现Comparable接口，可以通过Comparator 来实现比较算法进行排序,而且可以自定义升序还是降序

为Boy类实现Comparable接口,依据年龄排序

package com.perficient.basic;

import java.util.HashSet;
import java.util.Iterator;
import java.util.Set;
import java.util.TreeSet;

public class Boy implements Comparable{
	private String name;
	private int age;
	
	public Boy(String name, int age) {
		this.name = name;
		this.age = age;
	}

        //Getters and Setters......
        //依据年龄来排序
	
	public int compareTo(Object o) {
		int result = 0;
		Boy other = (Boy)o;
		if (this.age > other.age) result = 1;
		if (this.age < other.age) result = -1;
		return result;		     
	}

TreeSet能对集合采用自然排序,使用它去测试

public static void main(String[] args){
		Set<Boy> boys = new TreeSet<Boy>();
		Boy boy1 = new Boy("James", 28);
		Boy boy2 = new Boy("Hank", 40);
		Boy boy3 = new Boy("Billy", 15);
		
		boys.add(boy1);
		boys.add(boy2);
		boys.add(boy3);
		
		Iterator<Boy> it = boys.iterator();
		while (it.hasNext()){
			Boy boy = (Boy) it.next();
			System.out.println(boy.getName()+" age:" + boy.getAge());
		}

查看运行结果:

Billy age:15
James age:28
Hank age:40

创建Boy类的Comparator

package com.perficient.basic;

import java.util.Comparator;

public class BoyComparator implements Comparator<Boy>{
    //依据年龄进行比较
	public int compare(Boy boy1, Boy boy2) {
		int result = 0;
		if (boy1.getAge()> boy2.getAge()) result =1;
		if (boy1.getAge()< boy2.getAge()) result =-1;
		return result;		
	}
}

使用Arrays.sort()方法去测试BoyComparator类:

public static void main(String[] args){

		Boy boy1 = new Boy("James", 28);
		Boy boy2 = new Boy("Hank", 40);
		Boy boy3 = new Boy("Billy", 15);
				
		Boy[] boys2 = {boy1, boy2, boy3};
		Arrays.sort(boys2,  new BoyComparator());
		System.out.println(Arrays.toString(boys2));		
	}

运行结果

[Billy: 15, James: 28, Hank: 40]