Java如何从字符串实例化一个类 [英] Java how to instantiate a class from string
问题描述
可能的重复:
从 Java 中的变量创建新类
我有一个字符串
String className = "DummyClass"
现在我想创建一个类名是className的类对象,就像
Now I want to create a class object where the class name is className That is something like
Object className = new className() // I know it's not possible.
我想知道怎么做...
推荐答案
使用java.lang.reflect
" 将回答您的所有问题.首先使用 Class.forName()
获取 Class
对象,然后:
"Using java.lang.reflect
" will answer all your questions. First fetch the Class
object using Class.forName()
, and then:
如果我想实例化一个我用 forName()
检索到的类,我必须首先要求它提供一个 java.lang.reflect.Constructor
对象来表示我想要的构造函数,然后要求 Constructor
创建一个新对象.Class
中的方法 getConstructor(Class[] parameterTypes)
将检索一个 Constructor
;然后我可以通过调用它的方法newInstance(Object[] parameters)
来使用Constructor
:
If I want to instantiate a class that I retrieved with
forName()
, I have to first ask it for ajava.lang.reflect.Constructor
object representing the constructor I want, and then ask thatConstructor
to make a new object. The methodgetConstructor(Class[] parameterTypes)
inClass
will retrieve aConstructor
; I can then use thatConstructor
by calling its methodnewInstance(Object[] parameters)
:
Class myClass = Class.forName("MyClass");
Class[] types = {Double.TYPE, this.getClass()};
Constructor constructor = myClass.getConstructor(types);
Object[] parameters = {new Double(0), this};
Object instanceOfMyClass = constructor.newInstance(parameters);
Class
上有一个 newInstance()
方法,它似乎可以满足您的需求.不要使用它.它将已检查的异常默默地转换为未检查的异常.
There is a newInstance()
method on Class
that might seem to do what you want. Do not use it. It silently converts checked exceptions to unchecked exceptions.
请注意,此方法会传播空构造函数抛出的任何异常,包括已检查的异常.使用此方法可以有效地绕过编译器否则会执行的编译时异常检查.Constructor.newInstance
方法通过将构造函数抛出的任何异常包装在(已检查的)InvocationTargetException
中来避免此问题.
Note that this method propagates any exception thrown by the nullary constructor, including a checked exception. Use of this method effectively bypasses the compile-time exception checking that would otherwise be performed by the compiler. The
Constructor.newInstance
method avoids this problem by wrapping any exception thrown by the constructor in a (checked)InvocationTargetException
.
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