Java：使用类型参数访问私有构造函数

问题描述

这是关于的跟进。

假设我有以下类：

  class Foo< T> 
 {
 private T arg; 
 private Foo（T t）{
 // private！ 
 this.arg = t; 
} 
 
 @Override 
 public String toString（）{
 return我的参数是：+ arg; 
} 
} 
  

如何构建

根据，以下工作：

  public class示例{
 public static void main（final String [] args）throws Exception { 
构造函数< Foo>构造函数
 constructor = Foo.class.getDeclaredConstructor（Object.class）; 
 constructor.setAccessible（true）; 
 Foo< String> foo = constructor.newInstance（arg1）; 
 System.out.println（foo）; 
} 
} 
  

解决方案

将需要获取类，找到构造函数，它接受一个单一的参数与T的下限（在这种情况下，对象），强制构造函数是可访问的（使用 setAccessible 方法），最后使用所需的参数调用它。

This is a followup to this question about java private constructors.

Suppose I have the following class:

class Foo<T>
{
    private T arg;
    private Foo(T t) {
        // private!
        this.arg = t;
    }

    @Override
    public String toString() {
        return "My argument is: " + arg;
    }
}

How would I construct a new Foo("hello") using reflection?

ANSWER

Based on jtahlborn's answer, the following works:

public class Example {
    public static void main(final String[] args) throws Exception {
        Constructor<Foo> constructor;
        constructor = Foo.class.getDeclaredConstructor(Object.class);
        constructor.setAccessible(true);
        Foo<String> foo = constructor.newInstance("arg1");
        System.out.println(foo);
    }
}

解决方案

you would need to get the class, find the constructor which takes a single argument with the lower bound of T (in this case Object), force the constructor to be accessible (using the setAccessible method), and finally invoke it with the desired argument.

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