单例设计模式

/**
*
* 单例设计模式
*
*/
public class SingletonDemo {
public static void main(String[] args){
Singleton1 s=Singleton1.getInstance();
s.show();
Singleton1 s1=Singleton1.getInstance();
System.out.println(s==s1);

Singleton2 s2=Singleton2.getInstance();
s2.show();
Singleton2 s3=Singleton2.getInstance();
System.out.println(s2==s3);
}

}

//饿汉式
public class Singleton1 {
//定义一个本类对象并实例化
private static Singleton1 s=new Singleton1();
//构造方法私有化
private Singleton1(){};

public static Singleton1 getInstance(){
return s;
}
public void show(){
System.out.println("饿汉式单例模式");
}
}

//懒汉式(多线程访问时会有安全问题)
public class Singleton2 {
//定义一个本类对象
private static Singleton2 s=null;
//构造方法私有化
private Singleton2(){};

public static Singleton2 getInstance(){
if(s==null){
s=new Singleton2();
}
return s;
}
public void show(){
System.out.println("懒汉式单例模式");
}
}