Question

我们说我有以下代码

public class SuperClass {
    protected int super_class_value;

    public SuperClass (int value) {
        this.super_class_value = value;
    }
}

public class Subclass extends SuperClass {
    protected int subclass_value;

    public SubClass(int super_class_value, int subclass_value) {
        super(super_class_value);
        this.subclass_value = subclass_value;
    }
}

但是，现在我希望能够将SuperClass对象传递给SubClass构造函数。我该怎么做？

public SubClass(SuperClass super_class, int subclass_value) {
    //What do I do here?
    this.subclass_value = subclass_value;
}

基本上，我想做这样的事情......

public SubClass(SuperClass super_calss, int subclass_value) {
    super(super_class.super_class_value);
    this.subclass_value = subclass_value;
}

但如果SuperClass更复杂，我不想将每个值添加到super（）调用中。相反，我想简单地传入一个已经存在的对象，并将其用作超类。

我想这样做......

public SubClass(SuperClass super_class, int subclass_value) {
    super(super_class);
    this.subclass_value = subclass_value;
}

但我不确定是否允许这样做？

似乎我可以执行上述操作，如果我在SuperClass定义中添加构造函数。但那会是什么样的？

public class SuperClass {
    protected int super_class_value;

    public SuperClass (int value) {
        this.super_class_value = value;
    }

    public SuperClass (SuperClass super_class_object) {
        //What is done here?
    }
}

Answer 1

但是，现在我希望能够将SuperClass对象传递给 SubClass构造函数。我该怎么做？

你完全做同样的事情

public SubClass(SuperClass super_class, int subclass_value) {
    //What do I do here?
    // Do Whatever you want to do here ,
    this.subclass_value = subclas_value;
}

现在我想你可能正在考虑如何从子类传递Object到SuperClass然后这可以通过Java中的super keyword完成

super()用于调用直接父类构造函数。

现在将Object传递给SuperClass，在你的Subclass构造函数中，你的第一行必须是

super(super_class);

现在在你的超类中你必须有一个构造函数，它接受自身的Object，否则上面的行会抛出编译时错误

public SuperClass (SuperClass object) {
         // Do whatever you want to do .
          this.anyInstanceVariable=object.thatInstanceVariable;
    }

P.S。：我仍然不明白你想用这个来实现什么，但无论你提到什么，这都是你实现它的方式

<强>更新

正如您在评论中所说，您不想复制每个变量，那么您可以使用Object class的克隆方法

以下是一个如何在您的案例中实现它的示例

class SuperClass implements Cloneable{ // otherwise clone() method will throw CloneNotSupportedException

    int a;
    SuperClass obj=null; // this will point to the copy of the cloned object

    SuperClass(int a){// just to test that cloning is successfull
        this.a=a;
    }
    SuperClass(SuperClass a){
        try{
        this.obj=(SuperClass)a.clone();
        }
        catch(Exception e){
            e.printStackTrace();
        }
        display();
    }
    public void display(){// to Verify that Cloning has been done successfully
        try{
        System.out.println("Hello from cloned Object "+obj.a);
        }
        catch(Exception e){
            e.printStackTrace();
        }
    }
    @Override
    protected Object clone() throws CloneNotSupportedException  { // Overridden Method
        return super.clone();
    }
}

查看关于Object cloning in java

的这篇好文章

Answer 2

难道你不想只为你的超类提供copy constructor吗？

public class SuperClass {
    protected int super_class_value;

    public SuperClass (int value) {
        this.super_class_value = value;
    }
    protected SuperClass (SuperClass super_class) {
        this.super_class_value = super_class.supper_class_value;
    }
}

public class Subclass extends SuperClass {
    protected int subclass_value;

    public SubClass(SuperClass super_class, int subclass_value) {
        super(super_class);
        this.subclass_value = subclass_value;
    }
}

另请参阅此处有关撰写复制文件的问题：

Does Java have a default copy constructor (like in C++)?

Answer 3

您可以在SuperClass中添加getter方法，并在SubClass构造函数中使用它们。

public class SuperClass {
    protected int super_class_value;

    public SuperClass (int value) {
        this.super_class_value = value;
    }

    public int getSuperClassValue(){ return super_class_value;}
}

public class Subclass extends SuperClass {
    protected int subclass_value;

    public SubClass(SuperClass super_class, int subclass_value) {
        super(super_class.getSuperClassValue());
        this.subclass_value = subclass_value;
    }
}

Answer 4

查看Decorator Pattern以获取众所周知的示例。该页面包含一个带有UML图的好例子。

Answer 5

public class SuperClass {
    protected int super_class_value;

    public SuperClass (int value) {
        this.super_class_value = value;
    }

    Object obj = new Object();
}

public class Subclass extends SuperClass {
    protected int subclass_value;

    private SuperClass superCl = new SuperClass();

    public SubClass(int super_class_value, Object obj2 ,int subclass_value) {
        super(super_class_value);
        obj2 = superCl.obj;
        this.subclass_value = subclass_value;
    }
}

我应该如何使用超类的实例构造子类？

5 个答案: