Comparable是被类实现的一个借口为了能够对象本身和其他对象的比较，类本身必须实现此接口，以便能够比较它的实例。要求实现的方法是compareTo()。下面是一个例子：

class HDTV implements Comparable<HDTV> {
	private int size;
	private String brand;
 
	public HDTV(int size, String brand) {
		this.size = size;
		this.brand = brand;
	}
 
	public int getSize() {
		return size;
	}
 
	public void setSize(int size) {
		this.size = size;
	}
 
	public String getBrand() {
		return brand;
	}
 
	public void setBrand(String brand) {
		this.brand = brand;
	}
 
	@Override
	public int compareTo(HDTV tv) {
 
		if (this.getSize() > tv.getSize())
			return 1;
		else if (this.getSize() < tv.getSize())
			return -1;
		else
			return 0;
	}
}
 
public class Main {
	public static void main(String[] args) {
		HDTV tv1 = new HDTV(55, "Samsung");
		HDTV tv2 = new HDTV(60, "Sony");
 
		if (tv1.compareTo(tv2) > 0) {
			System.out.println(tv1.getBrand() + " is better.");
		} else {
			System.out.println(tv2.getBrand() + " is better.");
		}
	}
}
Sony is better.

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
 
class HDTV {
	private int size;
	private String brand;
 
	public HDTV(int size, String brand) {
		this.size = size;
		this.brand = brand;
	}
 
	public int getSize() {
		return size;
	}
 
	public void setSize(int size) {
		this.size = size;
	}
 
	public String getBrand() {
		return brand;
	}
 
	public void setBrand(String brand) {
		this.brand = brand;
	}
}
 
class SizeComparator implements Comparator<HDTV> {
	@Override
	public int compare(HDTV tv1, HDTV tv2) {
		int tv1Size = tv1.getSize();
		int tv2Size = tv2.getSize();
 
		if (tv1Size > tv2Size) {
			return 1;
		} else if (tv1Size < tv2Size) {
			return -1;
		} else {
			return 0;
		}
	}
}
 
public class Main {
	public static void main(String[] args) {
		HDTV tv1 = new HDTV(55, "Samsung");
		HDTV tv2 = new HDTV(60, "Sony");
		HDTV tv3 = new HDTV(42, "Panasonic");
 
		ArrayList<HDTV> al = new ArrayList<HDTV>();
		al.add(tv1);
		al.add(tv2);
		al.add(tv3);
 
		Collections.sort(al, new SizeComparator());
		for (HDTV a : al) {
			System.out.println(a.getBrand());
		}
	}
}
Output:

Panasonic
Samsung
Sony

通常我们可能会使用Collections.reverseOrder()方法来获得一个降序序列。如下所示：

ArrayList<Integer> al = new ArrayList<Integer>();
al.add(3);
al.add(1);
al.add(2);
System.out.println(al);
Collections.sort(al);
System.out.println(al);
 
Comparator<Integer> comparator = Collections.reverseOrder();
Collections.sort(al,comparator);
System.out.println(al);
Output:

[3,1,2]
[1,2,3]
[3,2,1]

3.什么时候使用哪一个呢？

方法一：TreeSet(Comparator comparator)

class Dog {
	int size;
 
	Dog(int s) {
		size = s;
	}
}
 
class SizeComparator implements Comparator<Dog> {
	@Override
	public int compare(Dog d1, Dog d2) {
		return d1.size - d2.size;
	}
}
 
public class ImpComparable {
	public static void main(String[] args) {
		TreeSet<Dog> d = new TreeSet<Dog>(new SizeComparator()); // pass comparator
		d.add(new Dog(1));
		d.add(new Dog(2));
		d.add(new Dog(1));
	}
}

class Dog implements Comparable<Dog>{
	int size;
 
	Dog(int s) {
		size = s;
	}
 
	@Override
	public int compareTo(Dog o) {
		return o.size - this.size;
	}
}
 
public class ImpComparable {
	public static void main(String[] args) {
		TreeSet<Dog> d = new TreeSet<Dog>();
		d.add(new Dog(1));
		d.add(new Dog(2));
		d.add(new Dog(1));
	}
}

原文：

Comparable vs Comparator in Java

Java中的Comparable与Comparator的区别,布布扣,bubuko.com

Java中的Comparable与Comparator的区别

原文：http://blog.csdn.net/sunling_sz/article/details/21232405