Java 的Comparable 和 Comparator

定义

顾名思义，Comparator是比较器，用于集合类排序时的参数，不需要在类中添加额外的代码
Comparable,可比较的，为一个比较的接口，类需要实现这个接口。集合类排序时候根据此类的compareTo 方法比较大小。

实现Comparable接口

下面demo为实现Comparable接口的方式，类内部需要实现compareTo 方法

package javaecho;

import java.util.Arrays;

public class MainClass implements Cloneable
{

public static void main(String args[]) throws CloneNotSupportedException
{
User u1 = new User(18,"allen");
User u2 = new User(20,"jack");
User[] list = {u2,u1};
for (User u :list)
System.out.println(u.getName());
Arrays.sort(list);
for (User u :list)
System.out.println(u.getName());
}
}

class User implements Comparable<User>
{
private int age;
private String name;
public User(int age,String name)
{
this.age= age;
this.name =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;
}
@Override
public int compareTo(User arg0) {
if(this.age>arg0.getAge())
return 1;
else if (this.age<arg0.getAge())
return -1;
else
return 0;
}

public boolean equals(Object arg0)
{
return true;
}
}

使用Comparator比较器

比较器的好处是灵活，无需在类中实现代码。但在集合类排序的时候，或者构造有序类集合时，需要作为参数传人进去。

package javaecho;

import java.util.Arrays;
import java.util.Comparator;

public class MainClass implements Cloneable
{

public static void main(String args[]) throws CloneNotSupportedException
{
User u1 = new User(18,"allen");
User u2 = new User(20,"jack");
User[] list = {u2,u1};
for (User u :list)
System.out.println(u.getName());
Arrays.sort(list, new Comparator<User>(){

@Override
public int compare(User arg0, User arg1) {
return arg0.getAge()> arg1.getAge() ? 1: (arg0.getAge()==arg1.getAge() ? 0: -1);
}

}
);
for (User u :list)
System.out.println(u.getName());
}
}

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