【Java】单例设计模式

package suziguang_d5_singleInstance;
public class A {
    private static A a = new A();
    private A()
    {}
    public static A getA()
    {
        return a;
    }
}

package suziguang_d5_singleInstance;
public class Test {
    public static void main(String[] args) {
        // A a = new A(); //error
        A a1 = A.getA();
        A a2 = A.getA();
        A a3 = A.getA();
        System.out.println(a1);
        System.out.println(a2);
        System.out.println(a3);
    }
}

package suziguang_d5_singleInstance;
public class B {
    private static B b = null;
    private B() {}
    public static B getB()
    {
        if(b == null) b = new B();
        return b;
    }
}

package suziguang_d5_singleInstance;
public class Test_B {
    public static void main(String[] args) {
        B b1 = B.getB();
        B b2 = B.getB();
        System.out.println(b1);
        System.out.println(b2);
    }
}