使用Reflection的参数化私有构造函数

Question

如何使用Reflection API访问参数化构造函数。我一直试图用下面的一组类来做它，但它会引发一些错误。

    //Primary class
    package com.deepak;

    public class A {
    private String name;

     private A(String name) {
            this.name = name;
        }

    }

//Exact class

    class MethodCall {

     Class first = Class.forName("com.deepak.A");
            Constructor constructor1 = first.getDeclaredConstructor();
            constructor1.setAccessible(true);
           A a= (A) constructor1.newInstance("deepak");
            System.out.println(a);


    }

错误讯息：

Exception in thread "main" java.lang.NoSuchMethodException: com.deepak.A.<init>()
    at java.lang.Class.getConstructor0(Class.java:3082)
    at java.lang.Class.getDeclaredConstructor(Class.java:2178)
    at com.deepak.MethodCall.main(MethodCall.java:44)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at com.intellij.rt.execution.application.AppMain.main(AppMain.java:147)

Answer 1

此Exception表示在relection中找不到constructor而没有param，因为班级A只有一个constructor接受String param。

所以你应getConstructor使用constructor parameter课程，例如：

 Constructor constructor1 = first.getConstructor(String.class);

Answer 2

您可以使用以下代码来获取所需内容：

public static void main(String[] args) throws Exception {
    Class first = Class.forName("com.deepak.A");
    Constructor[] declaredConstructors = first.getDeclaredConstructors();
    Constructor constructor1 = declaredConstructors[0];
    constructor1.setAccessible(true);
    A a= (A) constructor1.newInstance("deepak");
    System.out.println(a);

}