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javainner-classes
Sharon Watinsan
Sharon Watinsan

Reputation: 9850

Accessing variable from an inner class - getting null pointer exception

i want to access the arr variable from inside the inner class method MyMethod. When i try to print it from there i end up getting a null pointer exception.

public class MyClass{
    String[] arr;
    MyClass my;

    public MyClass(){
      my = new MyClass();
    }

     public class MyInner {
        public void MyMethod() {
            // I need to access 'my.arr' from here how can i do it. 
         }

       }

     public static void main(String[] args) {
       String[] n={"ddd","f"};

       my.arr=n;
     }
}

Upvotes: 0

Views: 3616

Answers (4)

Laf
Laf

Reputation: 8195

You haven't initialized it yet, so the reference is null. Initialize it in your constructor for example, and you will have access to the variable via your inner class.

public class MyClass {
    String[] arr;

    public MyClass (String[] a_arr) {
        arr = a_arr;
    }

    public class MyInner {
        public void MyMethod () {
            // I need to access 'my.arr' from here how can i do it. 
        }

    }

    public static void main (String[] args) {
        String[] n= {"ddd","f"};
        MyClass myClass = new MyClass (n);
    }
}

Upvotes: 1

Aakash Anuj
Aakash Anuj

Reputation: 3871

Do the following. Your way of initialization is wrong.

public class MyClass{
    String[] arr;
    MyClass my;

    public MyClass(){
    }

     public class MyInner {
        public void MyMethod() {
            // I need to access 'my.arr' from here how can i do it. 
         }

       }

     public static void main(String[] args) {
       String[] n={"ddd","f"};
       MyClass my=new MyClass();
String[] b = new String[2];

System.arraycopy( n, 0, b, 0, n.length );
     }
}

In case of more than 2 strings, simply do String[] b = new String[n.length];

Upvotes: 0

Aurand
Aurand

Reputation: 5537

Well, for starters in your main method you never create an instance of your class.

Also, MyClass has a reference to a MyClass object. In the constructor of MyClass, it initializes that reference by calling it's own constructor. That's an endless loop.

Upvotes: 0

Peter Lawrey
Peter Lawrey

Reputation: 533492

You can use just arr. However until you set it to something it will be null

BTW: Your my = new MyClass() will blow up as it will create objects until it stack overflows.

Upvotes: 3

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