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 [英] creating instance of object using reflection , when the constructor takes an array of strings as argument

问题描述

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

I am trying to create an instance of a class which has only the following constructor, overwriting the default constructor

public HelloWorld(String[] args)

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);

然后我试图为这个类创建一个对象

Then I am trying to create an object for this class

 obj = (HelloWorld)reflect.getConstructor(String[].class)
                          .newInstance(job1.arg_arr());

arg_arr() 用于将列表转换为字符串数组

arg_arr() is for converting a list to an array of strings

public String[] arg_arr(){
    String arg_list[]=new String[args.size()];
    return args.toArray(arg_list);
}

我在尝试创建实例时得到以下堆栈跟踪java.lang.IllegalArgumentException:

I get the following stack trace when trying to create the instance 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)

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.

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.

推荐答案

newInstance 接受一个 Object... 参数，所以当你给它一个 String[] 时它会通过它作为 Object[].

newInstance takes an Object... argument so when you give it a String[] it passes it as the Object[].

你想要的是以下内容，它告诉它你只传递一个参数，而不是数组的内容作为参数.

What you want is the following which tells it you are passing just one argument, not the contents of the array as arguments.

.newInstance((Object) job1.arg_arr())

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