集合(放对象)排序

用Collections.sort方法对list排序有两种方法
第一种是list中的对象实现Comparable接口，如下：
[java] view plain copy
/**
* 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：
[java] view plain copy
/**
* 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(HastSet——>List——>sort进行排序)：
public class Test {
public static void main(String[] args) {
User user1 = new User();
user1.setName("a");
user1.setPrice(11);
User user2 = new User();
user2.setName("b");
user2.setPrice(2);

Set<User> Hset = new HashSet<User>();
Hset.add(user2);
Hset.add(user1);

List<User> list = new ArrayList<User>();
list.addAll(Hset);


Collections.sort(list,new Comparator<User>(){
public int compare(User arg0, User arg1) {
return arg0.getPrice().compareTo(arg1.getPrice());
}
});
for(User u : list){
System.out.println(u.getName());
}
}


输出结果如下：
a
b

默认为升序，将。return arg0.getOrder().compareTo(arg1.getOrder()); 改为：
return arg1.getOrder().compareTo(arg0.getOrder());
就成降序的了。