強行對某個對象 collection 進行整體排序 的比較函數。可以將 Comparator 傳遞給 sort 方法(如
Collections.sort
或
Arrays.sort
),從而允許在排序順序上實現精確控制。還可以使用 Comparator 來控制某些數據結構(如有序 set
或有序映射
)的順序,或者爲那些沒有自然順序
的對象
collection 提供排序。需要實現compare方法,比較用來排序的兩個參數。根據第一個參數小於、等於或大於第二個參數分別返回負整數、零或正整數。
看一個例子:
// 定義一個Teacher類
package comparabletest;
/**
* @author Administrator 定義一個Teacher類
*/
public class Teacher {
private String name;
private int age;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
@Override
public String toString() {
return "Teacher [name=" + name + ", age=" + age + "]";
}
public Teacher(String name, int age) {
this.name = name;
this.age = age;
}
}
// 定義一個Teacher類的比較器
package comparabletest;
import java.util.Comparator;
/**
* @author Administrator 定義一個Teacher類的比較器,實現Comparator接口
*/
public class TeacherComparator implements Comparator<Teacher> {
@Override
public int compare(Teacher o1, Teacher o2) {
if (o1.getName().compareTo(o2.getName()) > 0) {
return -1; // 對象1的值大於對象2的值,返回-1.降序排列
} else if (o1.getName().compareTo(o2.getName()) < 0) {
return 1; // 對象1的值小於對象2的值,返回1.降序排列
} else {
if (o1.getAge() > o2.getAge()) {
return 1; // 對象1的值大於對象2的值,返回1.升序排列
} else if (o1.getAge() < o2.getAge()) {
return -1; // 對象1的值小於對象2的值,返回-1.升序排列
} else {
return 0;
}
}
}
}
// 測試代碼,將Teacher對象進行排序
package comparabletest;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
public class StudentCompare {
public static void main(String[] args) {
// 定義一個長度爲4的數組
Teacher[] teachers = { new Teacher("jack", 23), new Teacher("tom", 22),
new Teacher("peter", 21), new Teacher("jack", 28) };
// 按名字降序,年齡升序排列
java.util.Arrays.sort(teachers, new TeacherComparator());
for (int i = 0; i < teachers.length; i++) {
System.out.println(teachers[i]);
}
System.out.println("------");
// 定義一個長度爲4的列表
List<Teacher> teachersList = new ArrayList<Teacher>();
teachersList.add(new Teacher("jack", 23));
teachersList.add(new Teacher("tom", 22));
teachersList.add(new Teacher("peter", 21));
teachersList.add(new Teacher("jack", 28));
// 按名字降序,年齡升序排列
Collections.sort(teachersList, new TeacherComparator());
for (Teacher t : teachersList) {
System.out.println(t);
}
}
}
// 輸出結果:
Teacher [name=tom, age=22]
Teacher [name=peter, age=21]
Teacher [name=jack, age=23]
Teacher [name=jack, age=28]
------
Teacher [name=tom, age=22]
Teacher [name=peter, age=21]
Teacher [name=jack, age=23]
Teacher [name=jack, age=28]