Natural sorting: comparable interface, customized sorting: the difference between comparator interface

Catalog

1、 Natural ordering 、 Realization Comparable Interface

1. The first step is to define a test class  

2. Realization Comparable Interface , rewrite compareTo Method

Test code

Method 1 test results

Method 2 test results

2、 Custom sort ： Realization Comparator Interface

Test code

test result

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1、 Natural ordering 、 Realization Comparable Interface

1、 image string, integer When the wrapper class realizes Comparable Interface , Rewrote compareTo（obj） Method , The sorting method of comparing the size of two objects is given

2、 image string 、 The wrapper class overrides compareTo（） After method , From small to large

3、 rewrite compareTo（obj） The rules of ：

If the current object this Greater than the formal parameter object obj, Then return a positive integer , If the current object this Less than parameter object obj, Returns a negative number , If two objects are equal, return 0;

1. The first step is to define a test class  

package demo421.demo04;

import java.util.Comparator;

/**
 * @ founder  xiaoliu
 * @ Creation time  2022/4/23
 * @ describe 
 */
public class Person  {
    private String name;
    private int age;
    public Person(String name,int age){
        this.name=name;
        this.age=age;
    }
    public Person(){}

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

 

}

2. Realization Comparable Interface , rewrite compareTo Method

public class Person implements Comparable

   @Override
    public int compareTo(Object o) {
        if (o instanceof Person){
            Person p1 = (Person) o;
          
            // Mode one ：
/*
            if (this.age>p1.age){
                return 2;

            }else if (this.age< p1.age){
                return -1;
            }else {
                return this.name.compareTo(p1.name);
            }
*/
           /*  Mode two ： Use packaging compare（） Method 
            public static int compare(int var0, int var1) {
                return var0 < var1 ? -1 : (var0 == var1 ? 0 : 1);
            }*/
              if (this.name == p1.name){
                return Integer.compare(this.age,p1.age);
            }else{
                return this.name.compareTo(p1.name);
            }
    }
        throw new RuntimeException(" The type of input does not match ");
}

            // Comparison method 1 ： Manual comparison age Size , Then compare name
/*
            if (this.age>p1.age){
                return 2;

            }else if (this.age< p1.age){
                return -1;
            }else {
               return this.name.compareTo(p1.name);
            }

                // It's easier to understand it in this way
*/
           /* Mode two ： Use packaging compare（） Method , Because the wrapper class overrides compare（） Method , So you can use it directly .
            compare Source code ：public static int compare(int var0, int var1) {
                return var0 < var1 ? -1 : (var0 == var1 ? 0 : 1);
            }*/

         // Compare names first name, Compare your age age

  if (this.name == p1.name){
                return Integer.compare(this.age,p1.age);
            }else{
                return this.name.compareTo(p1.name);
            }

// It's simpler to write code like this

Test code

package demo421.demo04;

import javax.lang.model.element.VariableElement;
import java.util.Arrays;

/**
 * @ founder  xiaoliu
 * @ Creation time  2022/4/23
 * @ describe 
 */
public class Demo01 {
    public static void main(String[] args) {
        Person p1 = new Person("lwh", 20);
        Person p2 = new Person("ll", 20);
        Person p3 = new Person("ll", 32);
        Person p5 = new Person("ll", 21);
        Person p4 = new Person("bzd", 23);
        Person[] a = new Person[]{p1,p2,p3,p4,p5};
        Arrays.sort(a);
        System.out.println(Arrays.toString(a));

    }
}

Method 1 test results

Compare first age Compare again name, The test result is correct

[Person{name='ll', age=20}, Person{name='lwh', age=20}, Person{name='ll', age=21}, Person{name='bzd', age=23}, Person{name='ll', age=32}]

Method 2 test results

Compare first name, Compare again age, The test result is correct

[Person{name='bzd', age=23}, Person{name='ll', age=20}, Person{name='ll', age=21}, Person{name='ll', age=32}, Person{name='lwh', age=20}]

2、 Custom sort ： Realization Comparator Interface

1、 background ：

When the type of an element is not implemented java.lang.Comparable Interface and not convenient to modify the code ,

Or it does java.lang.Comparable The interface's collation is not suitable for the current operation ,

Then consider using Comparator To sort objects

Test code

package demo421.demo04;

import javax.lang.model.element.VariableElement;
import java.util.Arrays;
import java.util.Comparator;

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

    public static void main(String[] args) {
        Student s1 = new Student("lwh", 33);
        Student s2 = new Student("lwh", 22);
        Student s3 = new Student("aaa", 45);
        Student[] s = new Student[]{s1,s2,s3};
        Arrays.sort(s, new Comparator<Student>() {
            @Override
            public int compare(Student s1, Student s2) {

                if (s1.age > s2.age) {
                    return 3;
                } else if (s1.age < s2.age) {
                    return -2;
                } else {
                    return s1.name.compareTo(s2.name);
                }
            }
        });
        System.out.println(Arrays.toString(s));


    }
}

test result