Java8 method reference

Let's study Java 8 method references with you this time.

First of all, let's make an age sword method by the method before Java 8.

use lombok

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

import java.util.*;

public class App {
    public static void main( String[] args ) {
        List<Person> personList = new ArrayList<Person>();
        personList.add(new Person("Jack",25));
        personList.add(new Person("Mary",23));
        personList.add(new Person("Jill",24));
        personList.add(new Person("Dock",34));
        personList.add(new Person("Lily",27));


        //Anonymous class
        Collections.sort(personList, new Comparator<Person>() {
            @Override
            public int compare(Person o1, Person o2) {
                return o1.getAge() - o2.getAge();
            }
        });

        System.out.println(personList);
    }
}

@Data
@AllArgsConstructor
@NoArgsConstructor
class Person {
    private String name;
    private int age;
}

Implementation results: [Person (name = Mary, age = 23), Person (name = Jill, age = 24), Person (name = Jack, age = 25), Person (name = Lily, age = 27), Person (name = Dock, age = 34)]

Lambda expression

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

import java.util.*;

public class App {
    public static void main( String[] args ) {
        List<Person> personList = new ArrayList<Person>();
        personList.add(new Person("Jack",25));
        personList.add(new Person("Mary",23));
        personList.add(new Person("Jill",24));
        personList.add(new Person("Dock",34));
        personList.add(new Person("Lily",27));

        //Lambda expression
        Collections.sort(personList,(p1,p2) -> p1.getAge() - p2.getAge());
        System.out.println(personList);
    }
}

@Data
@AllArgsConstructor
@NoArgsConstructor
class Person {
    private String name;
    private int age;
    
}

Implementation results: [Person (name = Mary, age = 23), Person (name = Jill, age = 24), Person (name = Jack, age = 25), Person (name = Lily, age = 27), Person (name = Dock, age = 34)]

static method reference

import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;

import java.util.*;

public class App {
    public static void main( String[] args ) {
        List<Person> personList = new ArrayList<Person>();
        personList.add(new Person("Jack",25));
        personList.add(new Person("Mary",23));
        personList.add(new Person("Jill",24));
        personList.add(new Person("Dock",34));
        personList.add(new Person("Lily",27));

        //static method reference
        Collections.sort(personList, Person::CompareAge);
        System.out.println(personList);

    }
}

@Data
@AllArgsConstructor
@NoArgsConstructor
class Person {
    private String name;
    private int age;

    public static int CompareAge(Person o1, Person o2) {
        return o1.getAge() - o2.getAge();
    }
}