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; 
}