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：
- /**
- * 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(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。