/**
 * Created by liuyazhou on 2017/4/25.
 */
public class Singleton {

    //單例模式，懶漢式，缺點:每次建立新物件都要被鎖一次,優化後如下：
/*    
    private static Singleton  instance = null;
    private Singleton(){
    }
    public static synchronized Singleton getInstance(){
        if(instance == null){
            instance = new Singleton();
        }
        return instance;
    }
    */

    //這樣只會在第一次建立物件時鎖住，後面就不會再被鎖住
    private static Singleton  instance = null;
    private Singleton(){
    }
    private static synchronized void synInit(){
        if(instance == null){
            instance = new Singleton();
        }
    }

    public static  Singleton getInstance(){
        if(instance == null){
            synInit();
        }
        return instance;
    }
}