java 当构造函数将字符串数组作为参数时，使用反射创建对象实例
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原文地址: http://stackoverflow.com/questions/25610249/
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creating instance of object using reflection , when the constructor takes an array of strings as argument
提问by a curious engineer
I am trying to create an instance of a class which has only the following constructor, overwriting the default constructor
我正在尝试创建一个只有以下构造函数的类的实例，覆盖默认构造函数
public HelloWorld(String[] args)
I am doing the following
我正在做以下事情
Class reflect;
HelloWorld obj = null;
//some logic to generate the class name with full path
reflect = Class.forName(class_name);
Then I am trying to create an object for this class
然后我试图为这个类创建一个对象
obj = (HelloWorld)reflect.getConstructor(String[].class)
.newInstance(job1.arg_arr());
arg_arr()is for converting a list to an array of strings
arg_arr()用于将列表转换为字符串数组
public String[] arg_arr(){
String arg_list[]=new String[args.size()];
return args.toArray(arg_list);
}
I get the following stack trace when trying to create the instance
java.lang.IllegalArgumentException:
尝试创建实例时，我得到以下堆栈跟踪
java.lang.IllegalArgumentException：
wrong number of arguments
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
at java.lang.reflect.Constructor.newInstance(Constructor.java:408)
at processmigration.Process_manager.eval(Process_manager.java:175)
at processmigration.Process_manager.run(Process_manager.java:147)
at java.lang.Thread.run(Thread.java:745)
I wonder what is going wrong since I am passing only one argument to newInstance() just like the constructor of the class I am trying to create.
我想知道出了什么问题，因为我只向 newInstance() 传递一个参数，就像我试图创建的类的构造函数一样。
回答by Peter Lawrey
newInstancetakes an Object...argument so when you give it a String[] it passes it as the Object[].
newInstance接受一个Object...参数，所以当你给它一个 String[] 时，它会将它作为Object[].
What you want is the following which tells it you are passing just one argument, not the contents of the array as arguments.
您想要的是以下内容，它告诉它您只传递一个参数，而不是将数组的内容作为参数传递。
.newInstance((Object) job1.arg_arr())
回答by Dean Leitersdorf
The solution is as follows:
解决方法如下：
When performing getConstructor(...) and newInstance (...), all your arguments must be inside 1 array. Therefore, I created the arrays params and argsToPass and stored your args in them. Otherwise, it would thing your String[] is a list of arguments and not just 1 argument.
执行 getConstructor(...) 和 newInstance (...) 时，所有参数都必须在 1 个数组内。因此，我创建了数组 params 和 argsToPass 并将您的 args 存储在其中。否则，您的 String[] 会是一个参数列表，而不仅仅是 1 个参数。
Class reflect;
HelloWorld obj = null;
//some logic to generate the class name with full path
reflect = HelloWorld.class;
Class[] params = new Class[1];
params[0] = String[].class;
Object[] argsToPass = new Object[1];
argsToPass[0] = job1.arg_arr();
obj = (HelloWorld)reflect.getConstructor(params).newInstance(argsToPass);
EDIT: Tested code - works!!
编辑：经过测试的代码 - 有效！！
