Comparator接口位于：java.util包中。
Comparator接口：
1. 强行对某个对象的Collection进行整体排序。
值得注意的是：
Comparator接口可以作为参数传到一些sort()方法中，例如：
Collection.sort(List<T> list, Comparator<? super T> c)、
Arrays.sort(T[] a, Comparator<? super T> c);
2. Comparator接口指定的顺序，可以不是字典顺序排序，但包含字典顺序排序！！！
现在让我们仍然对User进行排序吧！！！
Let's do it!!!
3. 有的人会觉得 实现Comparator接口 有点奇怪，Comparator接口中明明有两个方法: compare()、equals()
为什么实现此接口的类只用实现compare()方法呢？
其实稍加思索，就明白了：实现Comparator接口的类没有实现equals方法，是因为类里有equals()方法了,
所有的类都是从基类java.lang.Object中继承的，而Object类中已经有equals()方法了，
故而在你创建完成这个类，就已经实现了equals()方法了，是不是恍然大悟呢？！！！
User类的代码如下：
package test;
public class User {
private String name;
private Integer age;
public User(String name, Integer age) {
this.name = name;
this.age = age;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public Integer getAge() {
return age;
}
public void setAge(Integer age) {
this.age = age;
}
@Override
public String toString() {
return "User [name=" + name + ", age=" + age + "]";
}
}
看下实现Comparator接口的类UserComparator的代码：
package test;
import java.util.Comparator;
public class UserComparator implements Comparator<User>{
@Override
public int compare(User o1, User o2) {
int flag = o1.getName().compareTo(o2.getName());
if(flag == 0) {
flag = o1.getAge().compareTo(o1.getAge());
}
return flag;
}
}
接着我们要进行测试了哈！UserTest.java的代码如下：
package test;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
public class UserTest {
public static void print(List<User> list) {
for(User u : list) {
System.out.println(u);
}
}
public static void print(User[] array) {
for(int i=0; i<array.length; i++) {
System.out.println(array[i]);
}
}
public static void main(String[] args) {
List<User> users = new ArrayList<User>();
users.add(new User("a",12));
users.add(new User("C",25));
users.add(new User("B",12));
users.add(new User("A",15));
users.add(new User("b",19));
users.add(new User("c",17));
users.add(new User("a",22));
User[] users2 = new User[]{
new User("a",12),
new User("C",25),
new User("B",12),
new User("A",15),
new User("b",19),
new User("c",17),
new User("a",22)
};
System.out.println("=========================Comparator接口的测试=========================");
System.out.println("List排序前：");
print(users);
System.out.println();
System.out.println();
System.out.println("List排序后：");
Collections.sort(users, new UserComparator());
print(users);
System.out.println("--------------------------------------------");
System.out.println();
System.out.println();
System.out.println();
System.out.println();
System.out.println("Array排序前：");
print(users2);
System.out.println();
System.out.println();
System.out.println("Array排序后：");
Arrays.sort(users2, new UserComparator());
print(users2);
}
}
测试的结果如下：
=========================Comparator接口的测试=========================
List排序前：
User [name=a, age=12]
User [name=C, age=25]
User [name=B, age=12]
User [name=A, age=15]
User [name=b, age=19]
User [name=c, age=17]
User [name=a, age=22]
List排序后：
User [name=A, age=15]
User [name=B, age=12]
User [name=C, age=25]
User [name=a, age=12]
User [name=a, age=22]
User [name=b, age=19]
User [name=c, age=17]
--------------------------------------------
Array排序前：
User [name=a, age=12]
User [name=C, age=25]
User [name=B, age=12]
User [name=A, age=15]
User [name=b, age=19]
User [name=c, age=17]
User [name=a, age=22]
Array排序后：
User [name=A, age=15]
User [name=B, age=12]
User [name=C, age=25]
User [name=a, age=12]
User [name=a, age=22]
User [name=b, age=19]
User [name=c, age=17]
以上是按照字典顺序进行排序，今天想着实现一个字典顺序的倒序排序，大家一起来讨论下吧！！
下面是UserComparator2的代码：
package test;
import java.util.Comparator;
public class UserComparator2 implements Comparator<User>{
@Override
public int compare(User o1, User o2) {
int flag = 0;
flag = sort(o1.getName(), o2.getName());
if(flag == 0) {
flag = o1.getAge().compareTo(o2.getAge());
}
return flag;
}
/*
* 字典顺序的倒序排序，z是第一个，A是最后一个,
* 如果A<B,返回1
* A=B,返回0
* A>B,返回-1
*/
public int sort(String s1, String s2) {
int flag = 0;
//获取s1、s2的字符序列
char[] c1 = s1.toCharArray();
char[] c2 = s2.toCharArray();
//设置循环的次数，取字符串长度小的
int length1 = s1.length();
int length2 = s2.length();
int longer = c1.length - c2.length;
int count = longer>=0 ? length2 : length1;
for(int i=0; i<count; i++) {
//取出每个字符串上对应的字符，进行比较
char charS1 = c1[i];
char charS2 = c2[i];
int result = charS1 - charS2;
if(result < 0) {
flag = 1;
break;
}else if(result > 0) {
flag = -1;
break;
}else {
flag = 0;
}
}
//如果是这种情况：jim、jime，则jime排在前
if(flag == 0) {
if(longer < 0) {
//长度长的排前面
flag = 1;
}else if(longer > 0) {
flag = -1;
}else {
flag = 0;
}
}
return flag;
}
}
然后，让我们开始进行测试吧：
package test;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
public class UserTest2 {
public static void print(List<User> list) {
for(User u : list) {
System.out.println(u);
}
}
public static void main(String[] args) {
List<User> users = new ArrayList<User>();
users.add(new User("jim",12));
users.add(new User("joe",25));
users.add(new User("jime",12));
users.add(new User("tom",15));
users.add(new User("tom",17));
users.add(new User("andy",19));
users.add(new User("cwayi",17));
users.add(new User("zendy",22));
users.add(new User("yorick",33));
users.add(new User("maomi",22));
System.out.println("=========================Comparator接口的测试=========================");
System.out.println("List排序前：");
print(users);
System.out.println();
System.out.println();
System.out.println("List排序后：");
Collections.sort(users, new UserComparator2());
print(users);
System.out.println("--------------------------------------------");
}
/*
* 预想的结果应该是：
* zendy--22
* yorick--33
* tom--15
* tom--17
* maomi--22
* joe--25
* jime--12
* jim--12
* cwayi--17
* andy--19
*/
}
程序运行的结果如下：
=========================Comparator接口的测试=========================
List排序前：
User [name=jim, age=12]
User [name=joe, age=25]
User [name=jime, age=12]
User [name=tom, age=15]
User [name=tom, age=17]
User [name=andy, age=19]
User [name=cwayi, age=17]
User [name=zendy, age=22]
User [name=yorick, age=33]
User [name=maomi, age=22]
List排序后：
User [name=zendy, age=22]
User [name=yorick, age=33]
User [name=tom, age=15]
User [name=tom, age=17]
User [name=maomi, age=22]
User [name=joe, age=25]
User [name=jime, age=12]
User [name=jim, age=12]
User [name=cwayi, age=17]
User [name=andy, age=19]
--------------------------------------------
是不是很有意思呢？！以上就是Comparator接口的学习了，快来一起学习吧！
