我們知道Comparable與Comparator接口都能使你的對象擁有你希望的順序,那麼爲什麼設計兩個接口呢?
我們看一下Comparable的使用場景:
package com.dusk;
/**
* Created by dushangkui on 2017/6/9.
*/
public class Student implements Comparable<Student> {
private String name;
private int age;
private String sex;
public Student(String name, int age, String sex) {
this.name = name;
this.age = age;
this.sex = sex;
}
@Override
public String toString() {
return "Student{" +
"name='" + name + '\'' +
", age=" + age +
", sex='" + sex + '\'' +
'}';
}
/*
* 先比較學生的年齡,年齡小的排在前面 如果年齡一樣再比較性別 女生排在前面
*/
@Override
public int compareTo(Student o) {
if(this.age>o.getAge())
return 1;
else if(this.age==o.getAge()){
if(this.sex==o.getSex()){
return 0;
}else if("女".equals(o.getSex())){
return 1;
}
}
return -1;
}
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;
}
public String getSex() {
return sex;
}
public void setSex(String sex) {
this.sex = sex;
}
}
場景類:
package com.dusk;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.TreeSet;
/**
* Created by dushangkui on 2017/6/9.
*/
public class Client {
public static void main(String[] args) {
Student stu1 = new Student("張三",22,"男");
Student stu2 = new Student("李四",20,"男");
Student stu3 = new Student("王五",20,"女");
Student stu4 = new Student("孫六",26,"女");
List<Student> students = new ArrayList<Student>(4);
students.add(stu1);
students.add(stu2);
students.add(stu3);
students.add(stu4);
System.out.println("原始數組: " + students);
Collections.sort(students);
System.out.println("排序後列表: " + students);
}
}
結果:
從上面我們可以看出來,Student類具有排序能力是通過實現Comparable接口,需要實現compareTo方法。
我們再看Comparator,現在有這樣一個場景,我手裏面有幾本書必須要讀,但是我這個人比較懶,只喜歡讀薄的書,看下面:
package com.dusk;
/**
* Created by dushangkui on 2017/6/9.
*/
public class Book {
private String name;
private int pageNum;
public Book(String name, int pageNum) {
this.name = name;
this.pageNum = pageNum;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getPageNum() {
return pageNum;
}
public void setPageNum(int pageNum) {
this.pageNum = pageNum;
}
@Override
public String toString() {
return "Book{" +
"name='" + name + '\'' +
", pageNum=" + pageNum +
'}';
}
}
場景類:
package com.dusk;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;
/**
* Created by dushangkui on 2017/6/9.
*/
public class BookClient {
public static void main(String[] args) {
Book b1 = new Book("Java入門到提高",560);
Book b2 = new Book("島上書店",260);
Book b3 = new Book("維基全書",25560);
List<Book> books =new ArrayList<Book>(3);
books.add(b1);
books.add(b2);
books.add(b3);
System.out.println("原始順序 "+ books);
Collections.sort(books, new Comparator<Book>(){
@Override
public int compare(Book b1, Book b2) {
return b1.getPageNum()-b2.getPageNum();
}
});
System.out.println("排序後順序 "+ books);
}
}
看結果:
從結果可以看出來,我們也得到了相同的順序,細心的童鞋可能已經發現了 我們的Book類並沒有實現Comparable接口。
這是怎麼實現呢,其實是通過策略模式。
其實兩個接口都可以實現相同的目的,只是使用的場景不同:
在實體類編寫的初期建議使用Comparable接口,如果不是自己的代碼或者想重寫排序邏輯請使用Comparator接口。