像Integer、String这些类型的数据都是已经实现Comparable接口的，所以对这些类型可以直接通过Arrays.sort(...)和Collections.sort(...)方法进行排序。但是对于一些自己new出来的对象而言，如果想使用sort这种方法，必须要实现Comparable接口，这是由sort方法底层决定的，具体看一下实例：

定义一个Bean

public class Employee implements Comparable{

private int age;  private String name;

public Employee(String name,int age){

this.name=name;

this.age=age;

}  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 hashCode() {

final int prime = 31;

int result = 1;

result = prime * result + age;

result = prime * result + ((name == null) ? 0 : name.hashCode());

return result;  }

@Override

public boolean equals(Object obj) {

if (this == obj)    return true;

if (obj == null)    return false;

if (getClass() != obj.getClass())

return false;

Employee other = (Employee) obj;

if (age != other.age)

return false;

if (name == null) {

if (other.name != null)

return false;

} else if (!name.equals(other.name))

return false;

return true;

}

@Override  public String toString() {

return "Employee [age=" + age + ", name=" + name + "]";

}

@Override

public int compareTo(Object o) {

if(o instanceof Employee){

if(age > ((Employee) o).age){

return 1;

}else if(age == ((Employee) o).age){

return 0;   }else if (age < ((Employee) o).age){

return -1;   }

}   return 0;

}

}

//

import java.util.ArrayList;

import java.util.Arrays;

import java.util.Collections;

import java.util.Comparator;

import java.util.List;

public class EmployeeSortTest {

public static void main(String[] args){

Employee[] staff = new Employee[3];

staff[0]= new Employee("aaa",12);

staff[1] = new Employee("bbb",13);

staff[2] = new Employee("ccc",14);

Arrays.sort(staff);//sort方法可以实现对对象数组的排序，但必须实现Comparable接口

for(Employee e: staff){

System.out.println(e);

}  //以上方法虽然可以实现对象的排序，但是有弊端；

//1、修改了公共类Employee，而很多情况下我们是没有办法修改公共的类，

//2、当我们需求满足不同的方式进行排序时，这种方法是不可行的

//接下来java中提供了Comparator接口，Comparator使用其compare()方法返回的整数来比较2个对象，

//这样就无需修改公共类

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

List<Employee> list = new ArrayList<Employee> ();

list.add(new Employee("aaa",12));

list.add(new Employee("bbb",13));

list.add(new Employee("bbb",14));

Collections.sort(list, new Comparator<Employee>(){

@Override

public int compare(Employee  o1, Employee  o2) {

// TODO Auto-generated method stub

return o1.getAge()-o2.getAge();

}

});

for(Employee e : list){

System.out.println(e);

}

}

}

//输出结果：

Employee [age=12, name=aaa]
Employee [age=13, name=bbb]
Employee [age=14, name=ccc]
Employee [age=12, name=aaa]
Employee [age=13, name=bbb]
Employee [age=14, name=bbb]