feat: Add singleton pattern example1

Author: hyeoni90

src/main/java/com/hyeonah/javalabs/designpattern/singleton/ex1/SystemSpeaker.java

@@ -0,0 +1,35 @@
+package com.hyeonah.javalabs.designpattern.singleton.ex1;
+
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+public class SystemSpeaker {
+ private static final Logger log = LoggerFactory.getLogger(SystemSpeaker.class);
+
+ private static SystemSpeaker instance;
+ private int volume;
+
+ private SystemSpeaker() {
+ volume = 5;
+ }
+
+ public static SystemSpeaker getInstance(){
+ if(instance == null){
+ instance = new SystemSpeaker();
+ log.info("new create system speaker -");
+ } else {
+ log.info("system speaker already exist!");
+ }
+
+ return instance;
+ }
+
+ public int getVolume() {
+ return volume;
+ }
+
+ public void setVolume(final int volume) {
+ this.volume = volume;
+ }
+}

src/main/java/com/hyeonah/javalabs/designpattern/singleton/ex1/SystemSpeakerMain.java

@@ -0,0 +1,25 @@
+package com.hyeonah.javalabs.designpattern.singleton.ex1;
+
+public class SystemSpeakerMain {
+
+ public static void main(final String[] args) {
+ final SystemSpeaker speaker1 = SystemSpeaker.getInstance();
+ final SystemSpeaker speaker2 = SystemSpeaker.getInstance();
+
+ /* 동일한 인스턴스 인지 볼륨 테스트 */
+ System.out.println(speaker1.getVolume()); //5
+ System.out.println(speaker2.getVolume()); //5
+
+ speaker1.setVolume(12);
+ System.out.println(speaker1.getVolume()); //12
+ System.out.println(speaker2.getVolume()); //13
+
+ speaker2.setVolume(33);
+ System.out.println(speaker1.getVolume()); //33
+ System.out.println(speaker2.getVolume()); //33
+
+ /* speaker1, speaker2의 인스턴스의 주소값이 같다는 것을 확인할 수 있다. */
+ System.out.println(speaker1); // SystemSpeaker@27a8c74e
+ System.out.println(speaker2); // SystemSpeaker@27a8c74e
+ }
+}