The way to initialize a class in another class

Question

While coding for a question about binary search tree on the Leetcode, I came with situation below:

public class TreeNode { int val; TreeNode left; TreeNode right; TreeNode(int x) { val = x; } } public class Solution { public List<Integer> inorderTraversal (TreeNode root) { // the variables below are defined by myself. Stack <TreeNode> stack = new Stack<TreeNode>(); ArrayList<Integer> res = new ArrayList<Integer>(); TreeNode curr = root; ... } }

In the last line, I define a TreeNode and make it equal to root. But if I wrote as

TreeNode curr = new TreeNode()

The compiler raises an error. I don't know why I cannot define a TreeNode as a temp variable in this way.

PM 77-1 · Accepted Answer · 2015-07-21 22:20:01Z

Your TreeNode class does not have a no-argument constructor.

Since you have defined a constructor with int parameter the compiler will not create a default constructor for you.

Something like this (assuming it makes sense) will work:

TreeNode cust = new TreeNode(someIntValue);

JoshTheLiuser · Accepted Answer · 2015-07-21 22:25:19Z

The TreeNode constructor has the parameter int x, so if you only write "TreeNode curr = new TreeNode ();", then there will be an error. All you need to do is add an int for the parameter.

Solution: "TreeNode curr = new TreeNode (4);"

Just add any int value.

Monads are like... · Accepted Answer · 2015-07-21 22:25:28Z

Java lets you use the default constructor (a constructor with no args) only in case you didn't explicitly created your own constructor in the class. Once you create your own constructor, in your case TreeNode(int x) { val = x; } you can no longer use the default constructor for that class.

Collectives™ on Stack Overflow

The way to initialize a class in another class

3 Answers 3

1 Comment

Comments

1 Comment

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

Comments

1 Comment

Related