如何在Java中将父项转换为子项 [英] How to cast parent into child in Java

问题描述

我正在这样做:

Child child = (Child)parent;

这给了我一个错误，我发现不可能这样做.我不知道为什么，但是我认为应该可以，如果Child类继承自Parent类，则它包含Parent对象数据.

Which gives me an error, I found it isn't possible to do it like this. I don't know exactly why, but I think it should be possible, if Child class inherits from Parent class, it contains the Parent object data.

我的问题是:

• 为什么不起作用?

• 如何在不设置每个单亲父母的情况下完成这项工作 这样的属性

• How can i make this work, without setting every single parent's attribute like this

:

class Parent{
    public int parameter1;//...
    public int parameter1000;
}

class Child extends Parent
{
    public Child(Parent parent)
{
        this.parameter1 = parent.parameter1;//...
        this.parameter1000 = parent.parameter1000;
}
}

推荐答案

好吧，你可以做一下:

Parent p = new Child();
// do whatever
Child c = (Child)p;

或者，如果您必须从纯父对象开始，则可以考虑在父类中包含一个构造函数并调用:

Or if you have to start with a pure Parent object you could consider having a constructor in your parent class and calling :

class Child{
    public Child(Parent p){
        super(p);
    }
}
class Parent{
    public Parent(Args...){
        //set params
    }
}

或构图模型:

class Child {
    Parent p;
    int param1;
    int param2;
}

在这种情况下，您可以直接设置父级.

You can directly set the parent in that case.

您还可以使用Apache Commons BeanUtils执行此操作.使用其BeanUtils类，您可以访问许多通过反射来填充JavaBeans属性的实用程序方法.

You can also use Apache Commons BeanUtils to do this. Using its BeanUtils class you have access to a lot of utility methods for populating JavaBeans properties via reflection.

要将所有公共/继承的属性从父对象复制到子类对象，可以使用其静态copyProperties()方法:

To copy all the common/inherited properties from a parent object to a child class object you can use its static copyProperties() method as:

BeanUtils.copyProperties(parentObj,childObject);

但是请注意，这是一项繁重的操作.

Note however that this is a heavy operation.

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