java Java反射：动态创建类实例并将其分配给父对象
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Java Reflection: Creating class instance dynamically and assigning it to Parent object
提问by Kazoom
String child = "C";
Parent p = null;
try {
Class c1 = new Class.forName(child);
Constructor co = c1.getConstructor();
// p=co.newInstance(null); //This gives compilatoin error cannot
// conver object to Parent
// p=(c1.getClass())co.newInstance(null);//also gives cast errror
p = (Parent) co.newInstance(null);// this works but it typecasts the
// child to Parent
} catch (Exception e) {
}
What am i trying to do.
我想做什么。
I have multiple Child classes inherited from Parent. I am getting child class name as string input.
我有多个继承自 Parent 的 Child 类。我正在获取子类名称作为字符串输入。
I want to instantiate the object of Child class and assign it to Parent. I do not want to type cast Child to Parent. As later in the code i need to compare two Child classes. If I typecast it to Parent. I cannot differentiate between Child1 and Child2.
我想实例化 Child 类的对象并将其分配给 Parent。我不想将 Child 类型转换为 Parent。在后面的代码中，我需要比较两个 Child 类。如果我将它类型转换为父级。我无法区分 Child1 和 Child2。
回答by Mark Peters
I don't think you understand what "typecasting" does. It has absolutely no effecton the object itself. Using p = (Parent) tsimply does a runtime check on tto make sure that the type of tis assignable to Parent(i.e. either tis-a Parentor it is-a subclass of Parent) . Afterward, twill still be a Child1or whatever its actualtype always has been.
我认为您不了解“类型转换”的作用。它对对象本身完全没有影响。Usingp = (Parent) t只是执行运行时检查t以确保 的类型t可分配给Parent（即tis-aParent或它是 的子类Parent）。之后，t仍将是 aChild1或其实际类型一直是。
Use the explicit cast.
使用显式转换。
回答by aroth
You might try something like:
您可以尝试以下操作：
Object parent = null;
String child = String.class.getName(); //not necessary, can just use String.class directly
Class childClass = Class.forName(child);
Class parentClass = Object.class;
if (parentClass.isAssignableFrom(childClass)) {
parent = childClass.newInstance();
}
System.out.println("Parent is: " + parent);
回答by Charlee Chitsuk
Even the Parent is cast form the 2 different children as
甚至 Parent 也是从 2 个不同的孩子中投射出来的
Parent parent1 = (Parent)child1;
Parent parent2 = (Parent)child2;
The parent1 and parent2 are totally different based on each child.
parent1 和 parent2 根据每个孩子是完全不同的。
You may see the difference by printing them as
您可以通过将它们打印为
System.out.println(parent1.getClass().getName());
System.out.println(parent2.getClass().getName());
Then you may compare it by using the getName() as well.
然后您也可以使用 getName() 进行比较。
I hope this may help to achieve the requirement.
我希望这可能有助于达到要求。
Regards,
问候，
Charlee Ch.
查理·Ch。
