Learning Design Patterns

1. Singleton Pattern

1. Eager initialization: The instance is created at the time of class initialization. It wastes some memory space but is thread-safe.

/**
 * @Autor LZH
 * @Date 2020/1/3  22:33
 */
public class EHan {
    //Eager initialization
    private static EHan instance=new EHan();
    //Private constructor
    private EHan(){
    }
    public static EHan getInstance(){
        return instance;
    }
}

2. Lazy initialization: The instance is only checked and created when needed. There are both thread-safe and non-thread-safe implementations. The following is a thread-safe and efficient approach (double-checked locking).

public class LHan {
    private LHan(){}//Private constructor

    private static LHan instance=null;//Lazy initialization

    public static LHan getInstance(){
        if (instance==null){
            synchronized(LHan.class){
                if(instance==null){
                    instance=new LHan();
                }
            }
        }
        return instance;
    }
}