Java單例模式的實現

原創

2020-02-20 13:40

1、懶漢式，線程安全

public class Singleton {

	private static Singleton instance;
	public Singleton() {
		// TODO Auto-generated constructor stub
	}
	public static synchronized Singleton getInstance(){
		if (instance == null) {
			instance = new Singleton();
		}
		return instance;
	}
}

2、餓漢式

public class Singleton {

	private static final Singleton instance = new Singleton();
	public Singleton() {
		// TODO Auto-generated constructor stub
	}
	public static Singleton getInstance(){
		return instance;
	}
}

3、雙重檢驗鎖

public class Singleton {

	private static volatile Singleton instance;//加上volatile取消jvm的重排序優化
	public Singleton() {
		// TODO Auto-generated constructor stub
	}
	public static Singleton getInstance(){
		if (instance == null) {                 //第一次檢驗
			synchronized (Singleton.class) {
				if (instance == null) {         //第二次檢驗
					instance = new Singleton();
				}
			}
		}
		return instance;
	}
}

4、內部靜態類

public class Singleton {

	private static class SingletonHolder{
		private static final Singleton INSTANCE = new Singleton();
	}
	public Singleton() {
		// TODO Auto-generated constructor stub
	}
	public static Singleton getInstance(){
		return SingletonHolder.INSTANCE;
	}
}