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How to call a private method that exists inside a private inner class

I want to test a private method that exists inside a private inner class

 public class MyBigClass {
    private class MyInnerClass {
       private void wantedMethod() {
       }
    }
 }

I want to call wantedMethod()to check it out

Here is my code

Class[] classes = MyBigClass.class.getDeclaredClasses();
    for (int i = 0; i < classes.length; i++) {
        // this code print "MyInnerClass"
        System.out.println(">> inner classes >> " + classes[i].getSimpleName());
        if (classes[i].getSimpleName().equals("MyInnerClass")) {
            Class clazz = classes[i];
            // Constructor c=clazz.getConstructor();
            Method[] methods = clazz.getDeclaredMethods();
            // this code print "wantedMethod"
            for (int j = 0; j < methods.length; j++) {
                System.out.println("inner class methods >>  " + methods[i].getName());
            }

        }

    }

Problem : I can not callwantedMethod()

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2 answers

If you want to call a non-static method, you need to specify on which object you want to call it. In your case, you need an internal class object, but since you do not have it, you need to create it. Because Java cannot allow you to create an object of an internal class without an external object of the class, you will also need to create this external object.

So these are the steps you need to take:

  • ( ),
  • ,
  • .

:
( , , , , , ).

try {
    //creating parent object
    Object outer = new MyBigClass();

    //creating inner class object
    Class<?> innerClass = Class.forName("MyBigClass$MyInnerClass");
    Constructor<?> constructor = innerClass.getDeclaredConstructor(MyBigClass.class);//inner object must know type of outer class
    constructor.setAccessible(true);//private inner class has private default constructor
    Object child = constructor.newInstance(outer);//inner object must know about its outer object

    //invoking method on inner class object
    Method method = innerClass.getDeclaredMethod("wantedMethod",new Class<?>[]{});
    method.setAccessible(true);//in case of unaccessible method
    method.invoke(child,new Object[]{});

} catch (ClassNotFoundException | NoSuchMethodException | SecurityException | InstantiationException | IllegalAccessException | IllegalArgumentException | InvocationTargetException e1) {
    // TODO Auto-generated catch block
    e1.printStackTrace();
}

+6

, CodeCircuit. if, .

Constructor c=clazz.getConstructor();, .

>> inner classes >> MyInnerClass
inner class methods >>  wantedMethod

.

    Class<?>[] classes = MyBigClass.class.getDeclaredClasses();

    for (Class<?> clazz : classes) {
        if(clazz.getSimpleName().equals("MyInnerClass")) {
            Method method = clazz.getDeclaredMethod("wantedMethod", new Class[] {});
            method.setAccessible(true);
            method.invoke(clazz.getDeclaredConstructor(MyBigClass.class).newInstance(new MyBigClass()), new Object[] {});
        }
    }

, . , , :

public MyInnerClass(MyBigClass bigClass) {
}

, Java () , .

, public .

public class MyBigClass {
    private class MyInnerClass {
        public MyInnerClass() {
            System.out.println("hello");
        }
        private void wantedMethod() {
            System.out.println("world");
        }
    }
}

setAccessible(true) , .

EDIT 2

, MyBigClass$MyInnerClass.class, , :

public class MyBigClass$MyInnerClass {
    public MyBigClass$MyInnerClass(MyBigClass paramMyBigClass) {
        System.out.println("hello");
    }
    private void wantedMethod() {
        System.out.println("world");
    }
}

, -

+2

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