java 如何在Java中将父项转换为子项
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How to cast parent into child in Java
提问by likaa
I am doing this:
我正在这样做：
Child child = (Child)parent;
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 Childclass inherits from Parentclass, it contains the Parentobject data.
这给了我一个错误，我发现不可能这样做。我不知道确切的原因，但我认为应该是可能的，如果Child类继承自Parent类，它包含Parent对象数据。
My questions are:
我的问题是：
- Why it doesnt work?
- 为什么它不起作用？
- How can i make this work, without setting every single parent's attribute like this
- 我怎样才能做到这一点，而不像这样设置每个父母的属性
:
：
class Parent{
public int parameter1;//...
public int parameter1000;
}
class Child extends Parent
{
public Child(Parent parent)
{
this.parameter1 = parent.parameter1;//...
this.parameter1000 = parent.parameter1000;
}
}
回答by Akash Roy Choudhury
Well you could just do :
那么你可以这样做：
Parent p = new Child();
// do whatever
Child c = (Child)p;
Or if you have to start with a pure Parent object you could consider having a constructor in your parent class and calling :
或者，如果您必须从纯 Parent 对象开始，您可以考虑在您的父类中有一个构造函数并调用：
class Child{
public Child(Parent p){
super(p);
}
}
class Parent{
public Parent(Args...){
//set params
}
}
Or the composition model :
或者组合模型：
class Child {
Parent p;
int param1;
int param2;
}
You can directly set the parent in that case.
在这种情况下，您可以直接设置父级。
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.
您还可以使用 Apache Commons BeanUtils 来执行此操作。使用它的 BeanUtils 类，您可以访问许多用于通过反射填充 JavaBeans 属性的实用方法。
To copy all the common/inherited properties from a parent object to a child class object you can use its static copyProperties() method as:
要将所有公共/继承属性从父对象复制到子类对象，您可以使用其静态 copyProperties() 方法：
BeanUtils.copyProperties(parentObj,childObject);
Note however that this is a heavy operation.
但是请注意，这是一项繁重的操作。
回答by Stephan-MDD
change 'this' to 'super' in your child constructor, and remove the parent parameter, instead replace that with the two parameters int parameter1;//...int parameter1000; :)
在子构造函数中将“this”更改为“super”，并删除父参数，而是将其替换为两个参数 int parameter1;//...int parameter1000; :)
class Parent{
public int parameter1;//...
public int parameter1000;
}
class Child extends Parent
{
public Child(int parameter1, int parameter1000)
{
super.parameter1 = parameter1
super.parameter1000 = parameter1000;
}
}
回答by Edye Chan
You can use json util to do this, such as fastjson.
您可以使用 json util 来执行此操作，例如 fastjson。
Child child = JSON.parseObject(JSON.toJSONString(parent), Child.class);
