[转]java List 排序 Collections.sort

java List 排序 Collections.sort

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： 代码: Java代码 /** * 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());         }    }             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());             }         }    }   /** * 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()); } } 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： 代码: Java代码 /** * 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;         }    }                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());            }         }    }   最简单的就是上面红色的字。。。。。。。。。。。 默认为升序，将。return arg0.getOrder().compareTo(arg1.getOrder());    改为： return arg1.getOrder().compareTo(arg0.getOrder());    就成倒序的了。。