Java中的比較器Comparable、Comparator

參考博客：java學習筆記13--比較器(Comparable、Comparator)

在Java代碼中，我們常常會面臨需要對集合進行排序的情況，這種情況下我們需要手動的定義Java比較器，告訴程序兩個對象如何比較大小。
Java中的比較器分為兩種Comparable和Comparator：

• Comparable：實現Comparable接口，並且重寫compareTo(T o)方法
• Comparator：實現Comparator接口，並且重寫compare()和equals()方法

Comparable實現

class Student implements Comparable<Student>{
	private String name;
	private int age;
	private float score;
	
	public Student(String name,int age,float score){
		this.name = name;
		this.age = age;
		this.score = score;
	}
	
	@Override
	public int compareTo(Student stu) {  //覆寫compareTo方法實現排序規則的應用
		if(this.score>stu.score){
			return -1;
		}else if(this.score<stu.score){
			return 1;
		}else{
			if(this.age>stu.age){
				return 1;
			}else if(this.age<stu.age){
				return -1;
			}else{
				return 0;
			}
		}
	}
	
	public String toString(){
		return "姓名："+this.name+", 年齡："+this.age+", 成績："+this.score;
	}
	
	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 float getScore() {
		return score;
	}
	public void setScore(float score) {
		this.score = score;
	}
	
	
}
 
public class T {
	public static void main(String[] args) throws Exception{
		Student stu[] = {new Student("張三",22,80f)
						,new Student("李四",23,83f)
						,new Student("王五",21,80f)};
		
		Arrays.sort(stu);   //進行排序操作
		for (int i = 0; i < stu.length; i++) {
			Student s = stu[i];
			System.out.println(s);
		}
	}
}

Compartor

package com.itmyhome;
 
import java.util.Comparator;
 
public class MyComparator implements Comparator<Student> {  //實現比較器
 
	@Override
	public int compare(Student stu1, Student stu2) {
		// TODO Auto-generated method stub
		if(stu1.getAge()>stu2.getAge()){
			return 1;
		}else if(stu1.getAge()<stu2.getAge()){
			return -1;
		}else{
			return 0;
		}
	}
 
}

class Student {
	private String name;
	private int age;
	
	public Student(String name,int age ){
		this.name = name;
		this.age = age;
	}
	
	public String toString(){
		return "姓名："+this.name+", 年齡："+this.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;
	}
}
 
public class T {
	public static void main(String[] args) throws Exception{
		Student stu[] = {new Student("張三",23)
						,new Student("李四",26)
						,new Student("王五",22)};
		Arrays.sort(stu,new MyComparator());             //對象數組進行排序操作
		
		List<Student> list = new ArrayList<Student>();
		list.add(new Student("zhangsan",31));
		list.add(new Student("lisi",30));
		list.add(new Student("wangwu",35));
		Collections.sort(list,new MyComparator());      //List集合進行排序操作
		
		for (int i = 0; i < stu.length; i++) {
			Student s = stu[i];
			System.out.println(s);
		}
		
		System.out.println("*********");
		
		for (int i=0;i<list.size();i++){
			Student s = list.get(i);
			System.out.println(s);
		}
	}
}