Java - 您可以从父类(super class)继承并拥有引用基类而不是父类的静态构造函数吗？

Question

看看下面的代码

class Parent{
    public static Parent instance = null;
    public Parent(){}
    public static Parent getInstance(){
        if (instance == null)
            instance = new Parent();
        return instance
    }
}

class Child extends Parent{
    public Child(){
        System.out.println("Child initialized.");
    }
}

如果我希望代码在每个子类中也创建一个静态实例，我是否必须复制getInstance的代码，或者这是否有效？

Answer 1

如果我没有误解的话，您想为每个子类创建一个单例，并且不想重复代码。如果将子类的类作为参数传递给 getInstance，则可能:

class Parent{
    public static HashMap<Class<? extends Parent>, Parent> instance 
                  = new HashMap<Class<? extends Parent>, Parent>();
    protected Parent(){}
    public static <T> T getInstance(Class<? extends Parent> cls) 
                    throws InstantiationException, IllegalAccessException{
        if (instance.get(cls) == null) {
            instance.put(cls, cls.newInstance());
        }
        return (T)instance.get(cls);
    }
}

class Child extends Parent{
    protected Child(){

    }
}

Child child = Child.getInstance(Child.class);