Singleton Patterns

• A popular design pattern where you only need ONE single instance in the entire application
• use static to share the instance

class Singleton {
    private static Singleton instance = new Singleton();
 
    private Singleton() {} // 외부 생성 차단
 
    public static Singleton getInstance() {
        return instance;
    }
}
 
// 사용
Singleton s = Singleton.getInstance();

• make the constructor private manage the instance with the static field
  • this guarantees that this is the only instance.. you can’t use the new keyword with this!
  • In Spring, the objects will often all be singletons