Singleton Pattern

Singleton Pattern 

어떠한 클래스가 유일하게 1개만 존재할 때 사용

 

서로 자원을 공유할 때 주로 사용

Ex) 실물 세계 : 프린터

      프로그래밍 : TCP Socket 통신에서 서버와 연결된 connect 객체

 

SocketClient.java

package com.company.design.singleton;

public class SocketClient {
    private static SocketClient socketClient = null;

    // default 생성자 private으로 막기
    // private SocketClient() {
    public SocketClient() {

    }

    // getInstance
    public static SocketClient getInstance() {

        // 자신이 가진 객체가 null 이면 새로 생성
        if(socketClient == null) {
            socketClient = new SocketClient();
        }

        // null 이 아닌 경우 return
        return socketClient;
    }

    public void connect() {
        System.out.println("connect");
    }
}

 

AClazz.java

package com.company.design.singleton;

public class AClazz {

    private SocketClient socketClient;

    public AClazz() {
        this.socketClient = new SocketClient();
       //this.socketClient = SocketClient.getInstance();
    }

    public SocketClient getSocketClient() {
        return this.socketClient;
    }
}

 

BClazz.java

package com.company.design.singleton;

public class BClazz {

    private SocketClient socketClient;

    public BClazz() {
        this.socketClient = new SocketClient();
        //this.socketClient = SocketClient.getInstance();
    }

    public SocketClient getSocketClient() {
        return this.socketClient;
    }
}

 

Main.java

package com.company.design;

import com.company.design.singleton.AClazz;
import com.company.design.singleton.BClazz;
import com.company.design.singleton.SocketClient;

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

        AClazz aClazz = new AClazz();
        BClazz bClazz = new BClazz();

        SocketClient aClient = aClazz.getSocketClient();
        SocketClient bClient = bClazz.getSocketClient();

        System.out.println("두 개의 객체가 동일한가 ? ");
        System.out.println(aClient.equals(bClient));
    }
}

 

싱글톤 패턴 사용한 경우

싱글톤 패턴 사용하지 않은 경우