Does extending a class require a hand-entered constructor in superclass?

Question

Hello,
Trying to extend a class (which doesn't have a main() method, if this matters), I got the following compiler message
NewInput.java:1: cannot resolve symbol
symbol : constructor InputFileDeclared ()
location: class InputFileDeclared
public class NewInput extends InputFileDeclared
After I hand-entered a blank constructor to the superclass the subclass have compiled.
Doesn't a class have a constructor by default?

Answer 1

If your class has a contructor which takes arguments, then the compiler does not provide you with a no-arg constructor. In this case if you need to have a constructor that takes no arguments then you need to write one.
If your base class had a constructor like
public class InputFileRead {
//Constructor
public InputFileRead( String fileName ) {
//Methods
and you wrote your Derived class with no constructor as
public class NewInput extends InputFileRead {
//No constructors
//Methods
Now when you write
NewInput nInp = new NewInput();
since you have not written any constructor for your new class the compiler will provide you with a default no-args constructor which will call the default constructor of your base class. Since there is no default constructor for your base class, you won't be able to instantiate the derived class.
You need to write a no-arg constructor for the new class which will then call the appropriate constructor of the base class.
public class NewInput extends InputFileRead {
//Constructor
public NewInput() {
super( "InputFile.txt" );
//Methods
}