CODEWITHSUNDEEP
javainheritanceconstructor
Timo
Timo

Reputation: 51

Error message appears compiling derived class

When I try to compile my derived class IntSearchTree, the error message 

IntSearchTree.java:3: error: constructor IntBinTree in class IntBinTree
cannot be applied to given types;

IntSearchTree(int node, IntSearchTree left, IntSearchTree right) {

required: int,IntBinTree,IntBinTree

found: no arguments

reason: actual and formal argument lists differ in length

1 error

, appears.

The following code shows the most important lines of the base class:

 class IntBinTree {
   int node;
   IntBinTree left;
   IntBinTree right;

   IntBinTree(int node, IntBinTree left, IntBinTree right) {
     this.node = node;
     this.left = left;
     this.right = right;
   }
 }

And the most important lines of the derived class:

 class IntSearchTree extends IntBinTree {
 IntSearchTree left;
 IntSearchTree right;

   IntSearchTree(int node, IntSearchTree left, IntSearchTree right) {
     this.node = node;
     this.left = left;
     this.right = right;
   }
 }

I tried to solve that problem by giving the constructor in the base clase the private modifier

 private IntBinTree(int node, IntBinTree left, IntBinTree right) {...}

, but the compiling error message was the same.

So the first question is how is it possible to define a constructor in a way that it is visible in the base class, but not in derived classes?

And the second question is, why is the base constructor still visible in the derived class, even if I use the private modifier?

Upvotes: 1

Views: 71

Answers (2)

macieg
macieg

Reputation: 11

I can see two problems with that implementation.

  1. You probably don't want to declare left and right fields again in your derived class - it's not causing a compilation error, but for sure will cause some problems hard to debug later.
  2. Creation of derived class requires calling a constructor of its super class - in that case, you could call super(node, left, right) in your current constructor, or super(). Remember that java creates by default public parameterless constructor for any class you create.

Upvotes: 1

Nexevis
Nexevis

Reputation: 4667

You need a no-args constructor.

Place this into your IntBinTree class:

IntBinTree()
{
}

Or you can use this instead in the IntSearchTree class:

IntSearchTree(int node, IntSearchTree left, IntSearchTree right) {
     super(node,left,right);
  }

When you do not have a no-args constructor in the super class, you need to explicitly call the constructor you want to use in the child class. This super() will call the constructor that takes in the node, left, right from IntBinTree().

Upvotes: 1

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