Java之Comparable，Comparator

package comparator;import java.util.Arrays;public class User implements Comparable<User> {private String id;private int age;public User(String id, int age) {this.id = id;this.age = age;}public int getAge() {return age;}public void setAge(int age) {this.age = age;}public String getId() {return id;}public void setId(String id) {this.id = id;}@Overridepublic int compareTo(User u) {return this.age - u.getAge();}public static void main(String[] args) {User[] users = new User[] { new User("a", 30), new User("b", 20) };//源码中可以看到调用了compareTo方法进行比较Arrays.sort(users);//从小到达排列//输出   b 20    a 30for (int i = 0; i < users.length; i++) {User user = users[i];System.out.println(user.getId() + " " + user.getAge());}}}package comparator;import java.util.Arrays;import java.util.Comparator;//强行对某个对象collection进行整体排序的比较函数，//可以将Comparator传递给Collections.sort或Arrays.sort。public class ComparatorDemo implements Comparator<String> {// 如果继承的是Comparator，则compare的两个方法是Object类型的@Overridepublic int compare(String o1, String o2) {// 比较String的大小即可return toInt(o1) - toInt(o2);}private int toInt(String str) {//String str = (String) str;str = str.replaceAll("一", "1");str = str.replaceAll("二", "2");str = str.replaceAll("三", "3");return Integer.parseInt(str);}public static void main(String[] args) {String[] array = new String[] { "一二", "三", "二" };// 查看其源码，可以看到其是通过调用ComparatorDemo的compare方法比较大小的// 两个参数则为array里面的值Arrays.sort(array, new ComparatorDemo());  //有小到达排列//最后输出     二      三     一二for (int i = 0; i < array.length; i++) {System.out.println(array[i]);}//可以尝试下面的方法//Collections.sort(list, c);}}package comparator;import java.util.ArrayList;import java.util.Arrays;import java.util.Collections;import java.util.Comparator;import java.util.List;public class UserComparator implements Comparator<User> {@Overridepublic int compare(User o1, User o2) {return o1.getAge() - o2.getAge();//默认升序排列}public static void main(String[] args) {User[] users = new User[] { new User("a", 30), new User("b", 20) };//运用UserComparator的compare方法进行比较Arrays.sort(users, new UserComparator());//输出  b 20a 30for (int i = 0; i < users.length; i++) {User user = users[i];System.out.println(user.getId() + " " + user.getAge());}List<User> list = new ArrayList<User>();list.add(new User("a", 30));list.add(new User("b", 20));//内部转化成数组进行比较 Collections.sort(list);//运用User实现的compareTo方法进行比较//输出  b 20a 30for (int i = 0; i < list.size(); i++) {User user = list.get(i);System.out.println(user.getId() + " " + user.getAge());}List<User> list2 = new ArrayList<User>();list2.add(new User("a", 30));list2.add(new User("b", 20));Collections.sort(list2, new UserComparator());//输出  b 20a 30for (int i = 0; i < list2.size(); i++) {User user = list2.get(i);System.out.println(user.getId() + " " + user.getAge());}}}