Scala class fields not visible

Question

I have the following class, nested in an object called Solution:

class TreeNode(l_son: TreeNode, r_son: TreeNode,
               l_val: Int, r_val:          


        

Answer 1

A declaration like class TreeNode(l_son: TreeNode, r_son: TreeNode, l_val: Int, r_val: Int, nr: Int) does not define any class members, just constructor arguments. You can still use them inside the class body almost as if they were members (except, you can't do this.l_son), because entire body is defined inside the constructor, so it's essentially a closure.

To define a class member as a constructor parameter, you have to prefix it with val or var in the constructor parameter list: class TreeNode(val l_son: TreeNode ...)

Case classes are special in that they will create a (immutable) member for every constructor parameter automatically, along with a bunch of other automatic members that make case classes useful.