check a binary tree is a binary search tree

gistfile1.java

public boolean checkBinarySearchTree(TreeNode r){
  if(r==null) return true;
  ArrayList<Integer> al=new ArrayList();
  Arraylist<Integer> arraylist=inOrderCreateArray(r, al);
  return sortedArrayList(arraylist);
  }
  public ArrayList inOrderCreateArray(TreeNode r, ArrayList<Integer> al){
    if (r!=null){
      
    if(r.left!=null)
      al=inOderCreateArray(r.left, al);
      
    al.add(r.data); 
    
    if(r.right!=null)
     al=inOdderCreateArray(r.right, al);
    }
    
    return al;
    
  }
  public boolean sortedArrayList(ArrayList<Integer> al){
     
    for(int i=0; i<al.size(); i++){
      if(al.get(i)>al.get(i+1)){
        return false;
      }
      
    }
    return true;
  }