Comparable接口与Comparator接口的比较————Comparator接口详解

Comparator接口位于：java.util包中。

Comparator接口：
1. 强行对某个对象的Collection进行整体排序。
值得注意的是：
Comparator接口可以作为参数传到一些sort()方法中，例如：
Collection.sort(List<T> list, Comparator<? super T> c)、
Arrays.sort(T[] a, Comparator<? super T> c);

2. Comparator接口指定的顺序，可以不是字典顺序排序，但包含字典顺序排序！！！

现在让我们仍然对User进行排序吧！！！
Let's do it!!!

3. 有的人会觉得 实现Comparator接口 有点奇怪，Comparator接口中明明有两个方法: compare()、equals()
为什么实现此接口的类只用实现compare()方法呢？
其实稍加思索，就明白了：实现Comparator接口的类没有实现equals方法，是因为类里有equals()方法了,
所有的类都是从基类java.lang.Object中继承的，而Object类中已经有equals()方法了，
故而在你创建完成这个类，就已经实现了equals()方法了，是不是恍然大悟呢？！！！

User类的代码如下：

package test;

public class User {

	private String name;
	private Integer age;

	public User(String name, Integer age) {
		this.name = name;
		this.age = age;
	}

	public String getName() {
		return name;
	}

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

	public Integer getAge() {
		return age;
	}

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

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

}

　　看下实现Comparator接口的类UserComparator的代码：

package test;

import java.util.Comparator;

public class UserComparator implements Comparator<User>{

	@Override
	public int compare(User o1, User o2) {
		int flag = o1.getName().compareTo(o2.getName());
		if(flag == 0) {
			flag = o1.getAge().compareTo(o1.getAge());
		}
		return flag;
	}

}

　　接着我们要进行测试了哈！UserTest.java的代码如下：

package test;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;

public class UserTest {

	public static void print(List<User> list) {
		for(User u : list) {
			System.out.println(u);
		}
	}

	public static void print(User[] array) {
		for(int i=0; i<array.length; i++) {
			System.out.println(array[i]);
		}
	}

	public static void main(String[] args) {

		List<User> users = new ArrayList<User>();
		users.add(new User("a",12));
		users.add(new User("C",25));
		users.add(new User("B",12));
		users.add(new User("A",15));
		users.add(new User("b",19));
		users.add(new User("c",17));
		users.add(new User("a",22));

		User[] users2 = new User[]{
				new User("a",12),
				new User("C",25),
				new User("B",12),
				new User("A",15),
				new User("b",19),
				new User("c",17),
				new User("a",22)
		};
		System.out.println("=========================Comparator接口的测试=========================");
		System.out.println("List排序前：");
		print(users);

		System.out.println();
		System.out.println();

		System.out.println("List排序后：");
		Collections.sort(users, new UserComparator());
		print(users);

		System.out.println("--------------------------------------------");
		System.out.println();
		System.out.println();
		System.out.println();
		System.out.println();

		System.out.println("Array排序前：");
		print(users2);

		System.out.println();
		System.out.println();

		System.out.println("Array排序后：");
		Arrays.sort(users2, new UserComparator());
		print(users2);

	}

}

　　测试的结果如下：

=========================Comparator接口的测试=========================
List排序前：
User [name=a, age=12]
User [name=C, age=25]
User [name=B, age=12]
User [name=A, age=15]
User [name=b, age=19]
User [name=c, age=17]
User [name=a, age=22]

List排序后：
User [name=A, age=15]
User [name=B, age=12]
User [name=C, age=25]
User [name=a, age=12]
User [name=a, age=22]
User [name=b, age=19]
User [name=c, age=17]
--------------------------------------------

Array排序前：
User [name=a, age=12]
User [name=C, age=25]
User [name=B, age=12]
User [name=A, age=15]
User [name=b, age=19]
User [name=c, age=17]
User [name=a, age=22]

Array排序后：
User [name=A, age=15]
User [name=B, age=12]
User [name=C, age=25]
User [name=a, age=12]
User [name=a, age=22]
User [name=b, age=19]
User [name=c, age=17]

以上是按照字典顺序进行排序，今天想着实现一个字典顺序的倒序排序，大家一起来讨论下吧！！

下面是UserComparator2的代码：

package test;

import java.util.Comparator;

public class UserComparator2 implements Comparator<User>{

	@Override
	public int compare(User o1, User o2) {
		int flag = 0;
		flag = sort(o1.getName(), o2.getName());
		if(flag == 0) {
			flag = o1.getAge().compareTo(o2.getAge());
		}
		return flag;
	}

	/*
	 * 字典顺序的倒序排序，z是第一个，A是最后一个,
	 * 如果A<B,返回1
	 * 	  A=B,返回0
	 * 	  A>B,返回-1
	 */
	public int sort(String s1, String s2) {
		int flag = 0;
		//获取s1、s2的字符序列
		char[] c1 = s1.toCharArray();
		char[] c2 = s2.toCharArray();
		//设置循环的次数，取字符串长度小的
		int length1 = s1.length();
		int length2 = s2.length();
		int longer = c1.length - c2.length;
		int count = longer>=0 ? length2 : length1;

		for(int i=0; i<count; i++) {
			//取出每个字符串上对应的字符，进行比较
			char charS1 = c1[i];
			char charS2 = c2[i];

			int result = charS1 - charS2;
			if(result < 0) {
				flag = 1;
				break;
			}else if(result > 0) {
				flag = -1;
				break;
			}else {
				flag = 0;
			}
		}

		//如果是这种情况：jim、jime，则jime排在前
		if(flag == 0) {
			if(longer < 0) {
				//长度长的排前面
				flag = 1;
			}else if(longer > 0) {
				flag = -1;
			}else {
				flag = 0;
			}
		}

		return flag;
	}

}

　　然后，让我们开始进行测试吧：

package test;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class UserTest2 {

	public static void print(List<User> list) {
		for(User u : list) {
			System.out.println(u);
		}
	}

	public static void main(String[] args) {
		List<User> users = new ArrayList<User>();
		users.add(new User("jim",12));
		users.add(new User("joe",25));
		users.add(new User("jime",12));
		users.add(new User("tom",15));
		users.add(new User("tom",17));
		users.add(new User("andy",19));
		users.add(new User("cwayi",17));
		users.add(new User("zendy",22));
		users.add(new User("yorick",33));
		users.add(new User("maomi",22));

		System.out.println("=========================Comparator接口的测试=========================");
		System.out.println("List排序前：");
		print(users);

		System.out.println();
		System.out.println();

		System.out.println("List排序后：");
		Collections.sort(users, new UserComparator2());
		print(users);

		System.out.println("--------------------------------------------");
	}
	/*
	 * 预想的结果应该是：
	 * 	zendy--22
	 *  yorick--33
	 *  tom--15
	 *  tom--17
	 *  maomi--22
	 *  joe--25
	 *  jime--12
	 *  jim--12
	 *  cwayi--17
	 *  andy--19
	 */

}

　　程序运行的结果如下：

=========================Comparator接口的测试=========================
List排序前：
User [name=jim, age=12]
User [name=joe, age=25]
User [name=jime, age=12]
User [name=tom, age=15]
User [name=tom, age=17]
User [name=andy, age=19]
User [name=cwayi, age=17]
User [name=zendy, age=22]
User [name=yorick, age=33]
User [name=maomi, age=22]

List排序后：
User [name=zendy, age=22]
User [name=yorick, age=33]
User [name=tom, age=15]
User [name=tom, age=17]
User [name=maomi, age=22]
User [name=joe, age=25]
User [name=jime, age=12]
User [name=jim, age=12]
User [name=cwayi, age=17]
User [name=andy, age=19]
--------------------------------------------

　　是不是很有意思呢？！以上就是Comparator接口的学习了，快来一起学习吧！