What's wrong with the following java code?

Question

I am getting some argument errors while compilation. don't know what wrong this.

I was expecting the output would be bj. since Class a doesn't have default constructor so at compilation time default constructor would be created by JVM. and the remaining output would be bj. Am I missing something?

class a
{

    a(String b)
    {
        System.out.println("this is a");
    }
}
class b extends a
{
    b()
    {
        System.out.println("b");
    }
}

class c extends b
{
    c(String j)
    {
        System.out.println(j);
    }
    public static void main(String...k)
    {
        new c("J");
    }
}

The error is shown below:

javac construct.java
construct.java:12: error: constructor a in class a cannot be applied to given ty
pes;
        {
        ^
  required: String
  found: no arguments
  reason: actual and formal argument lists differ in length
1 error

Answer 1

since Class a doesn't have default constructor so at compilation time default constructor would be created by JVM

The default constructor is created only if you don't define a custom constructor .

Your IDE should have shown you the following message on b() declaration:

There is no default constructor available in ' package .a'

When you tried to instantiate b , it did an implicit call to super() but found only a(String b) instead of a() . As the error message says, a(String b) expected a String but got no arguments.

The solution is either to create the parameterless a() constructor or call the a(String b) constructor in class b constructor.

class b extends a
{
    b()
    {
        super(""); // call to class a constructor passing some string as argument
        System.out.println("b");
    }
}

Answer 2

By convention you should name Java Classes in upper case letters

When new C("J"); is executed, it calls the constructor of class C . But as class C is extending class B , JVM will add

C(String j)
{
    super(); //added by JVM - calls the constructor of super class
    System.out.println("j");
}

So the constructor of class b is invoked and as it is also extending class A .

B()  
{  
   super();  //added by JVM
   System.out.println("b");
}

Now problem arises. As JVM will add default constructor in its implicit call. But there is no constructor defined with no-arguments. That's why you are getting an error. You can add super(""); in constructor B to resolve the error or create a constructor with no parameters.