CODEWITHSUNDEEP
java
John W
John W

Reputation: 171

What is the wrong with this java code?

I am learning java. The book I'm reading has a question which asks what is wrong with the following code? I have typed the code in NetBeans and I can see the error but why is this error caused and how is it resolved?

The error is highlighted over the code public A(int t) and it says

Constructor B in class B cannot be applied to given types, require int, found no arguments, reason actual and formal arguments lists differ in length.

Here is the code:

public class Test {
    public static void main(String[] args) {
       B b = new B(5);
    }
}

class A extends B {
    public A(int t)  {
        System.out.println("A's constructor is invoked");
    }
}

class B  {
    public B(int k)   {
        System.out.println("B's constructor is invoked");
    }
}

Upvotes: 2

Views: 262

Answers (4)

PermGenError
PermGenError

Reputation: 46408

when your super class has an args constructor and doesn't have a no-args constructor you have to explicitly invoke it using a super(args) call from sub-class constructor

class A extends B {
     public A(int t)  {
         super(t);
            System.out.println("A's constructor is invoked");
        }

}

Upvotes: 4

Reimeus
Reimeus

Reputation: 159774

You need to call the constructor of the super class as the first statement in A(int):

public A(int t)  {
   super(t);
   System.out.println("A's constructor is invoked");
}

Upvotes: 1

Code-Apprentice
Code-Apprentice

Reputation: 83527

The class B has only one constructor which takes an int argument. On the other hand, the constructor you have in class A (implicitly) tries to call a constructor in A's super class (namely B) that takes no arguments. This is the cause of the error. There are at least two ways to fix the problem:

  1. Create a no-arg constructor in class B.

  2. Explicitly call the constructor in class B which takes an int as a parameter. You can do this using the super keyword.

Upvotes: 1

zch
zch

Reputation: 15278

Class B has defined constructor, so it does not have public implicit default constructor (with no arguments). All subclass constructors have to explicitly call superclass constructors, via super(t), if zero argument superclass constructor is not available.

Upvotes: 1

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