Question

I need to create an array of trees and take a letter typed by a user and place it into a node. I am getting a NullPointerException error with forest[i].root. How can I fix this?

class TreeApp  
{  
 public static void main(String[] args) throws IOException  
 {  
    Tree forest[] = new Tree[10];  

    Scanner kb = new Scanner(System.in);  

    for(int i = 0; i < 10; i++)  
    {  
        System.out.println("Insert a letter: "); 

        Node newNode = new Node();  
        newNode.iData = kb.next().charAt(0);  

        System.out.println("node: " + newNode.iData );  

        forest[i].root = newNode;
        }  
     }
  }

Answer 1

Tree forest[] = new Tree[10]; 

The above statement creates an array of type Tree, but it does not store any Tree instances into the array. So, your array elements are initialized with default null value.

You need to initialize your array elements first before accessing them.

Add this line in your for loop: –

forest[i] = new Tree();

before accessing forest[i].root.