用collection.sort（）方法对list集合排序

第一种是list中的对象实现Comparable接口，如下：

/**
* 根据order对User排序
*/
public class User implements Comparable<User>{ private String name; private Integer order; public String getName() { return name; } public void setName(String name) { this.name = name; } public Integer getOrder() { return order; } public void setOrder(Integer order) { this.order = order; } public int compareTo(User arg0) { return this.getOrder().compareTo(arg0.getOrder()); }
}

测试一下：

public class Test{public static void main(String[] args) { User user1 = new User(); user1.setName("a"); user1.setOrder(1); User user2 = new User(); user2.setName("b"); user2.setOrder(2); List<User> list = new ArrayList<User>(); //此处add user2再add user1 list.add(user2); list.add(user1); Collections.sort(list); for(User u : list){ System.out.println(u.getName()); } }
}

输出结果如下 
a 
b

第二种方法是根据Collections.sort重载方法来实现，例如：

/**
* 根据order对User排序
*/
public class User { //此处无需实现Comparable接口 private String name; private Integer order; public String getName() { return name; } public void setName(String name) { this.name = name; } public Integer getOrder() { return order; } public void setOrder(Integer order) { this.order = order; }
}

主类中这样写即可：

public class Test{ public static void main(String[] args) { User user1 = new User(); user1.setName("a"); user1.setOrder(1); User user2 = new User(); user2.setName("b"); user2.setOrder(2); List<User> list = new ArrayList<User>(); list.add(user2); list.add(user1); Collections.sort(list,new Comparator<User>(){ public int compare(User arg0, User arg1) { return arg0.getOrder().compareTo(arg1.getOrder()); } }); for(User u : list){ System.out.println(u.getName()); } }
}

输出结果如下 
a 
b 
前者代码结构简单，但是只能根据固定的属性排序，后者灵活，可以临时指定排序项，但是代码不够简洁

多字段的场合：

Collections.sort(list,new Comparator<User>(){ public int compare(User arg0, User arg1) {
//            第一次比较专业 int i = arg0.getOrder().compareTo(arg1.getOrder());
//            如果专业相同则进行第二次比较 if(i==0){
//                第二次比较 int j=arg0.getXXX().compareTo(arg1.getXXX());
//                如果学制相同则返回按年龄排序 if(j==0){ return arg0.getCCC().compareTo(arg1.getCCC()); } return j; } return i; } });

以下是另外一个例子

package test;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
public class ArrayListTest {
public static void main(String[] args) {
ArrayList<Exmployee> arrayList  = new ArrayList<Exmployee>() ;
arrayList.add(new Exmployee("zengqiang",new Integer(5000))) ;
arrayList.add(new Exmployee("zengmin",new Integer(4000))) ;
arrayList.add(new Exmployee("liuxiaojuan",new Integer(4200))) ;
arrayList.add(new Exmployee("giuming",new Integer(2200))) ;
Collections.sort(arrayList, new Comparator<Exmployee>(){
public int compare(Exmployee arg0, Exmployee arg1) {
return  arg1.getSalary()-arg0.getSalary() ; //按照工资升序
//return  arg0.getSalary()-arg1.getSalary() ; 按照工资降序
//return arg0.getName().compareTo(arg1.getName()) ; 按照姓名升序 }
});
for(Exmployee e:arrayList)
System.out.println(e.getName()+"'s salary is "+e.getSalary()) ;
}
}
class Exmployee {
public Exmployee(String name, int salary) {
this.name = name ;
this.salary = salary ;
}
private String name;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getSalary() {
return salary;
}
public void setSalary(int salary) {
this.salary = salary;
}
private int salary;
}