Thread: AVL Tree help.

I just need some help figuring why I'm getting a NullPointerException where the "height" starts under the insert method. I posted the whole code before but some editing errors happened and if you wanna see the whole code again I can paste that in again but I just need help specifically on this.

I'm just getting an error beginning at "if(t.left().height() - t.right().height() == 2){"

Am I using this the wrong way? I feel like the way i'm coding that part to find the height of the left tree is incorrect.

[/COLOR]

 
//constructor
	public static class AvlTreeNode{
		private int value;
		private AvlTreeNode left;
		private AvlTreeNode right;
		private int height;
 
		public AvlTreeNode(int value, AvlTreeNode left, AvlTreeNode right){
			this.value = value;
			this.left = null;
			this.right = null;
			height = 0;
		}
                public AvlTreeNode(int value){
                this.value = value;
                left = null;
                right = null;
                }
 
		public AvlTreeNode left(){
			return this.left;
		}
 
		public AvlTreeNode right(){
			return this.right;
		}
 
		public int value(){
			return this.value;
		}
		public int height(){
			return this.height;
		}
	}
	//method to insert a new node and number to a tree
	public static AvlTreeNode insert(AvlTreeNode t, int x){
		if(t == null){
			t = new AvlTreeNode(x,null,null);
			return t;
		}else if(x < t.value()){
			t.left = insert(t.left(), x);
		}else if(x > t.value()){
			t.right = insert(t.right(), x);
		}
		if(t.left().height() - t.right().height() == 2){
			if(x < t.left.value()){
				t = singleRotateWithLeft(t);
			}
			else if(x > t.left().value()){
				t = doubleRotateWithLeft(t);
			}
			else if(x > t.value()){
				t.right = insert(t.right(), x);
			}
		}
		return t;
	}