Comparable和Comparator详解---java

程序员文章站 2022-05-23 14:16:48

...

Comparable和Comparator

java.lang.Comparable 传入一个对象与自己比较—>内比较器

接口中定义的方法：

public interface Comparable<T> {
    public int compareTo(T o);
}

用Comparable来排序字符

import java.util.Collections;
import java.util.*;

public class ComparableTest01
{
	public static void main(String[] args){
		Person p1 = new Person("001","abc");
		Person p2 = new Person("002","bcd");
		Person p3 = new Person("003","aaa");
		List<Person> list = new ArrayList();
		List<Person> list1 = new LinkedList();

		list.add(p1);
		list.add(p2);
		list.add(p3);

		list1.add(p1);
		list1.add(p2);
		list1.add(p3);

		Collections.sort(list);
		Collections.sort(list1);

		System.out.println("ArrayList------->Comparable");
		list.forEach(System.out::println);
		System.out.println("LinkedList------->Comparable");
		list1.forEach(System.out::println);
		
	}
}

class Person implements Comparable<Person>
{
	String id;
	String name;
	
	public Person(String id,String name){
		this.id = id ;
		this.name = name;
	}
	public int compareTo(Person p ){
        //直接调用String的comparTo()方法
		return this.name.compareTo(p.name);
		
	}
	public String toString(){
		 return "Person{" +
                "name='" + name + '\'' +
                ", id='" + id + '\'' +
                '}';
	}
}

用Comparable比较数字

import java.util.*;
import java.util.Collections;

public class ComparableTest02
{
	public static void main(String[] args){
		Person p1 = new Person("abc",1);
		Person p2 = new Person("bcd",2);
		Person p3 = new Person("aaa",3);
		List<Person> list = new ArrayList();
		List<Person> list1 = new LinkedList();

		list.add(p1);
		list.add(p2);
		list.add(p3);

		list1.add(p1);
		list1.add(p2);
		list1.add(p3);

		Collections.sort(list);
		Collections.sort(list1);

		System.out.println("ArrayList------->Comparable");
		list.forEach(System.out::println);
		System.out.println("LinkedList------->Comparable");
		list1.forEach(System.out::println);
		
	}
}
//泛型必须写
class Person implements Comparable<Person>
{
	String name;
	int id;
	public Person(String name,int id){
		this.name = name ;
		this.id = id ;
	}
	public String toString(){
		return "Person{" +
                "name='" + name + '\'' +
                ", id='" + id + '\'' +
                '}';
	}
	public int compareTo(Person p){
        //直接相减就行
		return this.id - p.id;
	}
}

运行结果：
Comparable和Comparator详解---java

java.util.Comparator 传入两个对象，进行比较—>外比较器

接口中的定义的方法：

public interface Comparator<T> {
	int compare(T o1, T o2);
	//省略其他方法...
}

下面用Comparator来比较字母

import java.text.Collator;
import java.util.*;

public class ComparatorTest
{
	public static void main(String[] args){
        Student t3 = new Student("003","小菜鸡");
		Student t1 = new Student("001","马云");
		Student t2 = new Student("002","马化腾");
		
		List<Student> list = new LinkedList();
		List<Student> list1 = new ArrayList();
		list.add(t1);
		list.add(t2);
		list.add(t3);
		
		list1.add(t1);
		list1.add(t2);
		list1.add(t3);

		Collections.sort(list,new SortId());
		Collections.sort(list1,new SortId());
		System.out.println("LinkedList---->根据id排序：");
		//Lambda表达式
		list.forEach(System.out::println);
		
		System.out.println("ArrayList---->根据id排序：");
		list1.forEach(System.out::println);
	}
}

class SortId implements Comparator<Student>{
	public int compare(Student t1 , Student t2){
		Comparator<Object> c = Collator.getInstance();
		return c.compare(t1.id,t2.id);
	}
	
}

class Student
{
	String id;
	String name;
	public Student(String id,String name){
		this.id = id;
		this.name = name;
	}
	public String toString(){
		return "Student{" +
                "name='" + name + '\'' +
                ", id='" + id + '\'' +
                '}';
	}
}

运行结果：

Comparable和Comparator详解---java

下面用Comparator来比较数字

import java.text.Collator;
import java.util.*;

public class ComparatorTest01
{
	public static void main(String[] args){

	Student t3 = new Student(3,"马云");
	Student t1 = new Student(1,"马云");
	Student t2 = new Student(2,"马化腾");
	
	List<Student> list = new LinkedList();
	List<Student> list1 = new ArrayList();
	
	list.add(t1);
	list.add(t2);
	list.add(t3);
	
	list1.add(t1);
	list1.add(t2);
	list1.add(t3);
	
	//采用匿名内部类
	Collections.sort(list,new Comparator<Student>(){
		public int compare(Student o1,Student o2){
			return o1.id-o2.id;
		}
	});
	//采用lambda表达式
	Collections.sort(list1,(o1,o2)->  o1.id-o2.id);
	System.out.println("LinkedList----->根据（int）类型的id排序");
	list.forEach(System.out::println);
	System.out.println("LinkedList----->根据（int）类型的id排序");
	list1.forEach(System.out::println);

	}
}

class Student
{
	int    id;
	String name;
	public Student(int id,String name){
		this.id = id;
		this.name = name;
	}
	public String toString(){
		return "Student{" +
                "name='" + name + '\'' +
                ", id='" + id + '\'' +
                '}';
	}
}

下面用Comparator来比较汉字(汉字和字母不一样，但是java给程序员提供了方法，只是不是太准确…)

import java.text.Collator;
import java.util.*;

public class ComparatorTest03
{
	public static void main(String[] args){
			Student t3 = new Student(3,"安琪拉");
			Student t1 = new Student(1,"马云");
			Student t2 = new Student(2,"马化腾");
			
			List<Student> list = new LinkedList();
			List<Student> list1 = new ArrayList();
			
			list.add(t1);
			list.add(t2);
			list.add(t3);
			
			list1.add(t1);
			list1.add(t2);
			list1.add(t3);

			Collections.sort(list,new Comparator<Student>(){
				
				public int compare(Student o1,Student o2){
					Comparator<Object> c  = Collator.getInstance(Locale.CHINA);
					return c.compare(o1.name,o2.name);
				}
			});

//lambda表达式
			Collections.sort(list1,
				(o1,o2)->{
				
					Comparator<Object> c  = Collator.getInstance(Locale.CHINA);
				    return c.compare(o1.name,o2.name);

			            });

			System.out.println("LinkedList----->根据（int）类型的id排序");
			list.forEach(System.out::println);
			System.out.println("LinkedList----->根据（int）类型的id排序");
			list1.forEach(System.out::println);
	}
}

class Student
{
	int    id;
	String name;
	public Student(int id,String name){
		this.id = id;
		this.name = name;
	}
	public String toString(){
		return "Student{" +
                "name='" + name + '\'' +
                ", id='" + id + '\'' +
                '}';
	}
}

运行结果：

Comparable和Comparator详解---java

下面来试试这个题：

使用Comparator排序
1.1 按学生年龄排序(升，降)
1.2 按学生性别排序(升，降)
1.3 按学生学号排序(升，降)
1.4 按学生姓名排序(升，降)
1.5 按学生年龄排序，年龄相同时再按性别排序，性别也相同时再按姓名排，姓名也相同时再按学号排


import java.text.Collator;
import java.util.*;

public class ComparatorTest04 {
    public static void main(String[] args) {
        Student student1 = new Student(23,"男","马云","123");
        Student student4 = new Student(24,"男","赵云","231");
        Student student7 = new Student(23,"男","安琪拉","223");
        Student student5 = new Student(27,"男","大小姐","132");
        Student student6 = new Student(23,"男","安琪拉","123");
        Student student2 = new Student(56,"女","貂蝉","123");
        Student student3 = new Student(23,"女","阿吊","322");

        List<Student> list = new ArrayList<>();
        list.add(student1);
        list.add(student2);
        list.add(student3);
        list.add(student4);
        list.add(student5);
        list.add(student6);
        list.add(student7);

        Collections.sort(list,
	(o1,o2)->{
	
	Comparator<Object> s = Collator.getInstance(Locale.CHINA);
		if(o1.age-o2.age==0){

		    if(s.compare(o1.sex,o2.sex)==0){
			if(s.compare(o1.name,o2.name)==0){
			    return s.compare(o1.id,o2.id);
			}
			return s.compare(o1.name,o2.name);
		    }
		    return s.compare(o1.sex,o2.sex);
		}
		return o1.age-o2.age;
	
	});
        list.forEach(System.out::println);
    }
}


class Student {
    int age ;
    String sex ;

    String name;
    String id;

    public Student(int age, String sex, String name, String id) {
        this.age = age;
        this.sex = sex;
        this.name = name;
        this.id = id;
    }

    @Override
    public String toString() {
        return "Student{" +
                "age=" + age +
                ", sex='" + sex + '\'' +
                ", name='" + name + '\'' +
                ", id='" + id + '\'' +
                '}';
    }
}

运行结果：

Comparable和Comparator详解---java

Comparable接口和Comparator接口的区别

Comparable接口位于java.lang包下；Comparator则在java.util包下
要实现Comparable接口，必须重写comparaTo()方法，主要偏向于传入一个值和自己比较，一般是内部使用；而实现Comparator接口可以在类外部使用，主要偏向于两个值比较。
Comparable接口中只有一个compareTo()方法；但是Comparator接口不仅提供了compara()方法，还提供了其他默认方法，如reversed()、thenComparing()，使我们可以按照更多的方式进行排序。

上一篇： Java 挽救的比较器(Comparator)

下一篇： java-Comparator

Comparable和Comparator详解---java

Comparable和Comparator

java.lang.Comparable 传入一个对象与自己比较—>内比较器

java.util.Comparator 传入两个对象，进行比较—>外比较器

Comparable接口和Comparator接口的区别

Java 向上转型和向下转型的详解

Java 语言中关键字“static”的理解和应用详解

详解JAVA里面获取map的key和value的方法

详解Java中的checked异常和unchecked异常区别

Java的数据类型和参数传递(详解)

Java中增强for循环的实现原理和坑详解

设置和获取当前线程名称（java代码大全及详解）

详解java nio中的select和channel

java集合类型（java集合类详解和使用）

java多线程关键字final和static详解