java-Comparable和Comparator的用法

太过爱你忘了你带给我的痛 2021-11-09 14:04 315阅读 0赞

### Java中的排序和比较中经常用到Comparable和Comparator这两个接口，这两个接口都可以重写该比较方法，实现除了基本数据类型外的实体类的字段比较和排序，这里讲三个方法扩展接口的应用。 ###

**\[Comparable扩展类\]:**

class StuComparable implements Comparable<StuComparable> {
    	private int age;
    	private String name;
    
    	/**
    	 * @param age
    	 * @param name
    	 */
    	public StuComparable(int age, String name) {
    		this.age = age;
    		this.name = name;
    	}
    
    	public int getAge() {
    		return age;
    	}
    
    	public void setAge(int age) {
    		this.age = age;
    	}
    
    	public String getName() {
    		return name;
    	}
    
    	public void setName(String name) {
    		this.name = name;
    	}
    
    	/**
    	 * 接口重写，实现年龄排序
    	 */
    	@Override
    	public int compareTo(StuComparable stu) {
    		return this.getAge() - stu.getAge();
    	}
    
    }

【**Comparator扩展类\]:**

class StuComparator implements Comparator<StuComparator> {
    	private int age;
    	private String name;
    
    	/**
    	 * @param age
    	 * @param name
    	 */
    	public StuComparator(int age, String name) {
    		this.age = age;
    		this.name = name;
    	}
    
    	public int getAge() {
    		return age;
    	}
    
    	public void setAge(int age) {
    		this.age = age;
    	}
    
    	public String getName() {
    		return name;
    	}
    
    	public void setName(String name) {
    		this.name = name;
    	}
    
    	@Override
    	public int compare(StuComparator o1, StuComparator o2) {
    		return o1.getAge() - o2.getAge();
    	}
    
    }

**一.Collections.sort() **

**重写Comparable接口：比较2个对象的大小**

ArrayList<StuComparable> arrayList = new ArrayList<StuComparable>();
    arrayList.add(new StuComparable(6, "123"));
    arrayList.add(new StuComparable(5, "456"));
    arrayList.add(new StuComparable(4, "789"));
    // 1.Sort方法用到了Comparable接口，Student重写Comparable接口方法，可以进行排序
    // 解决方案一：如果StuComparable类不实现Comparable接口，会报错，因为sort中不知道如何对实        
    // 体类比较大小               
    // Collections.sort(arrayList );
    // 解决方案二： Student类不实现Comparable接口，传进去一个Comparator接口对象
    Collections.sort(arrayList , new Comparator<StuComparable>() {
    @Override
    public int compare(Student o1, Student o2) {
    return o1.getAge() - o2.getAge();
    }
    });
    for (StuComparable stu : arrayList) {
    System.out.println(MessageFormat.format("age:{0}", stu.getAge()));
    }

**二.TreeMap**

**重写Comparable接口：比较2个对象的大小**

// 解决方案一：如果StuComparable类不实现Comparable接口，会报错，因为put中不知道如何对实体类进行比较                             
    TreeMap<StuComparable, String> treeMap = new TreeMap<StuComparable, String>();
    // 解决方案二： Student类不实现Comparable接口，传进去一个Comparator接口对象
    // TreeMap<StuComparable, String> treeMap = new TreeMap<StuComparable, String>(new
    // Comparator<StuComparable>() {
    // public int compare(Student o1, Student o2) {
    // return o1.getAge() - o2.getAge();
    // }
    // });
    treeMap.put(new StuComparable(6, "kobe"), "kobe");
    treeMap.put(new StuComparable(5, "jordan"), "jordan");
    treeMap.put(new StuComparable(4, "davis"), "davis");
    Set<Entry<StuComparable, String>> allSet = treeMap.entrySet();
    for (Entry<StuComparable, String> entry : allSet) {
    System.out.println(MessageFormat.format("key:{0},value:{1}", entry.getKey().getAge(), entry.getValue()));
    }

**三.Arrays.sort**

**重写Comparator接口：比较2个对象的大小**

StuComparable[] stuArr = { new StuComparable(6, "123"), new StuComparable(5, "456"),
    				new StuComparable(4, "789") };
    		Arrays.sort(stuArr);
    		for (StuComparable stu : stuArr) {
    			System.out.println(MessageFormat.format("age:{0}", stu.getAge()));
    		}

**输出结果：升序排序**

![2019080115553187.png][]

[2019080115553187.png]: /images/20211109/23f4f67e556e43f596c6fd2b543da479.png