Lambdaの実装を練習

test for Lambda

package test;

import java.util.ArrayList;
import java.util.List;

public class PersonFind {
    public static void main(String[] args) {
        List<Person> persons = new ArrayList<>();
        persons.add(new Person("name10", 10));
        persons.add(new Person("name20", 20));
        persons.add(new Person("name30", 30));
        persons.add(new Person("name40", 40));
        persons.add(new Person("name50", 50));
        System.out.println("-- 1 filter ---------------------------");
        persons.stream().filter(p->p.getAge() >= 30).forEach(p -> System.out.println("★1  30以上:" + p.getName()));        
        System.out.println("-- 2 findFirst ---------------------------");
//        Optional<Person> firstPerson = 
        Object xxx = persons.stream().filter(p->p.getAge() == 20).findFirst();
//        Optional<Person> xxx = persons.stream().filter(p->p.getAge() == 20).findFirst();
        System.out.println("★2 firstPerson:" + xxx);
//        System.out.println((Optional)xxx.get.getName());
        System.out.println("-- 3 map & sum  ---------------------------");
//        int total = persons.stream().map(p->p.getAge()).sum();
//        System.out.println("total:" + total);
         Object m = persons.stream().map(p->p.getAge());
         System.out.println("☆3 map:" + m);
        System.out.println("-- 4 map & forEach  ---------------------------");
         persons.stream().filter(p->p.getAge() < 20).map(p->p.getAge()).forEach(p->System.out.println("★4 map forEach:" + p));
        System.out.println("-- 5 map & into  ---------------------------");
        List<Person> list = persons.stream().filter(p->p.getAge() <= 20).into(new ArrayList<Person>());
        list.forEach(p-> System.out.println("★5 map Into:" + p.getName()));
    }
}

public class Person {
    String name;
    int age;

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public int getAge() {
        System.out.println("getAge:" + age);
        return age;
    }
}