单利模式

public class Stinglegon2 {
	//懒汉模式
	private Stinglegon2(){
		
	}
	private static Stinglegon2 stinglegon2=null;
	
	public static Stinglegon2 getstinglegon(){
		if(stinglegon2==null){
			return stinglegon2=new Stinglegon2();
		}else{
			return stinglegon2;
		}
		
	}
}

public class Stinglegon {
	//饿汉模式
	private Stinglegon(){//构造方法私有
		
	}
	private  static final Stinglegon stinglegon=new Stinglegon();//又因为静态只能调静态，所以要加static。final修饰成员为常量
	public static synchronized Stinglegon getStinglegon(){//因为构造方法被私有不能new对象，所以就用静态类名.方法。
		return stinglegon;
	}
}

测试

public class TextDemo {

	public static void main(String[] args) {
		Stinglegon s1=Stinglegon.getStinglegon();
		Stinglegon s2=Stinglegon.getStinglegon();
		boolean a=s1.equals(s2);
		System.out.println(a);
		System.out.println(s1==s2);
		System.out.println("-----------------");
		
		Stinglegon2 ss1=Stinglegon2.getstinglegon();
		Stinglegon2 ss2=Stinglegon2.getstinglegon();
		boolean aa=ss1.equals(ss2);
		System.out.println(aa);
		System.out.println(ss1==ss2);
	
	}

}

结果
true
true

true
true