💜 01. 동작 파라미터화 코드 | Predicate | 익명클래스 | lambda (Thread) | ExecutorService

🤥 JAVA 8 잘 안쓰고, 고전적인 방식만 써서... 이번에 스터디 해보도록..

이 카테고리는 말이 많기 보다는.. 코드로 보여주도록 할거다. 내가 다시 보고 기억하기 쉬운 용으로..

🍎 사과 클래스

무게와 색상 정보가 담긴 사과 클래스 생성

package javaStudy.mda02;

/**
 * 사과
 */
public class Apple {
    public enum Color {
        RED,
        GREEN
    }

    Color color;
    Integer weight;

    public Apple(Color color, int weight) {
        this.color = color;
        this.weight = weight;
    }

    public Color getColor() {
        return color;
    }

    public void setColor(Color color) {
        this.color = color;
    }

    public Integer getWeight() {
        return weight;
    }

    public void setWeight(Integer weight) {
        this.weight = weight;
    }

    @Override
    public String toString() {
        return "Apple{" +
                "color=" + color +
                ", weight=" + weight +
                '}';
    }
}

📌 Predicate 생성

Predicate 참/거짓을 반환하는 함수

인터페이스

---

package javaStudy.mda02;

public interface ApplePredicate {
    boolean test(Apple apple);
}

초록색 사과만 선택

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package javaStudy.mda02;

public class AppleGreenColorPredicate implements ApplePredicate{
    @Override
    public boolean test(Apple apple) {
        return Apple.Color.GREEN.equals(apple.getColor());
    }
}

무거운 사과만 선택

---

package javaStudy.mda02;

public class AppleHeavyWeightPredicate implements ApplePredicate{

    @Override
    public boolean test(Apple apple) {
        return apple.getWeight() > 150;
    }
}

📌 Main Method

package javaStudy.mda02;

import java.util.*;

import static java.util.stream.Collectors.groupingBy;
import static java.util.stream.Collectors.toList;

public class MainMethod {
    
    public static void main(String[] args) {
        List<Apple> appleList = Arrays.asList(
                new Apple(Apple.Color.RED, 180),
                new Apple(Apple.Color.GREEN, 100),
                new Apple(Apple.Color.GREEN, 350),
                new Apple(Apple.Color.RED, 400)
        );
        /**
         * 무거운 사과만
         * [Apple{color=RED, weight=180}, Apple{color=GREEN, weight=350}, Apple{color=RED, weight=400}]
         */
        filterApples(appleList, new AppleHeavyWeightPredicate());

        /**
         * 익명 클래스
         * Apple{color=GREEN, weight=100}, Apple{color=GREEN, weight=350}]
         */
        filterApples(appleList, new ApplePredicate() {
            @Override
            public boolean test(Apple apple) {
                return Apple.Color.GREEN.equals(apple.getColor());
            }
        });

        /**
         * 람다식 (빨간 사과만)
         * [Apple{color=RED, weight=180}, Apple{color=RED, weight=400}]
         */
        filterApples(appleList, (Apple apple) -> Apple.Color.RED.equals(apple.getColor()));
        
        /**
         * compareTo (가벼운 사과 순)
         * [Apple{color=GREEN, weight=100}, Apple{color=RED, weight=180}, Apple{color=GREEN, weight=350}, Apple{color=RED, weight=400}]
         */
        appleList.sort((Apple a1, Apple a2) -> a1.getWeight().compareTo(a2.getWeight()));
        
        /**
         * stream lambda (무게 150 넘는 사과만 무게순으로 정렬)
         * [180, 350, 400]
         */
        List<Integer> lambdaTest = appleList.stream().filter(apple -> apple.getWeight() > 150).sorted(Comparator.comparing(Apple::getWeight)).map(Apple::getWeight).collect(toList());
        
        /**
         * groupingBy (색상별 정리)
         * {GREEN=[Apple{color=GREEN, weight=100}, Apple{color=GREEN, weight=350}], RED=[Apple{color=RED, weight=180}, Apple{color=RED, weight=400}]}
         */
        Map<Apple.Color, List<Apple>> groupingTest = appleList.stream().collect(groupingBy(Apple::getColor));
    }

    /**
     * 사과 필터
     *
     * @param inventory
     * @param p
     * @return
     */
    public static List<Apple> filterApples(List<Apple> inventory, ApplePredicate p) {
        List<Apple> result = new ArrayList<>();
        for (Apple apple : inventory) {
            if (p.test(apple)) {
                result.add(apple);
            }
        }
        return result;
    }
}

📌 Main Method2

package javaStudy.mda02;

import java.util.Arrays;
import java.util.List;

public class MainMethod2 {
    public static void main(String[] args) {
        List<Apple> appleList = Arrays.asList(
                new Apple(Apple.Color.RED, 180),
                new Apple(Apple.Color.GREEN, 100),
                new Apple(Apple.Color.GREEN, 350),
                new Apple(Apple.Color.RED, 400)
        );

        /**
         * 무게순 정렬 (List sort 및 Comparator 활용
         * [Apple{color=GREEN, weight=100}, Apple{color=RED, weight=180}, Apple{color=GREEN, weight=350}, Apple{color=RED, weight=400}]
         */
        appleList.sort((Apple a1, Apple a2) -> a1.getWeight().compareTo(a2.getWeight()));
        
        /**
         * Runnable lambda 전
         */        
        Thread t = new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.println("Hello world");
            }
        });
        
        /**
         * Runnable lambda 후
         */
        Thread t_lambda = new Thread(() -> System.out.println("Hello World"));
    }
}

Reference

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모던 자바 인 액션 (한빛미디어)