Java error: Implicit super constructor is undefined for default constructor

Question

I have a some simple Java code that looks similar to this in its structure: ``` abstract public class BaseClass { String someString; public BaseClass(String someString) { this.someString = someString; } abstract public String getName(); } public class ACSubClass extends BaseClass { public ASubClass(String someString) { super(someString); } public String getName() { return "name value for ASubClass"; } } ``` I will have quite a few subclasses of `BaseClass`, each implementing the `getName()` method in its own way (template method pattern). This works well, but I don't like having the redundant constructor in the subclasses. It's more to type and it is difficult to maintain. If I were to change the method signature of the `BaseClass` constructor, I would have to change all the subclasses. When I remove the constructor from the subclasses, I get this compile-time error: `Implicit super constructor BaseClass() is undefined for default constructor. Must define an explicit constructor` Is w…

Accepted Answer

You get this error because a class which has no constructor has a default constructor, which is argument-less and is equivalent to the following code:

```
public ACSubClass() {
    super();
}
```

However since your BaseClass declares a constructor (and therefore doesn't have the default, no-arg constructor that the compiler would otherwise provide) this is illegal - a class that extends BaseClass can't call `super();` because there is not a no-argument constructor in BaseClass.

This is probably a little counter-intuitive because you might think that a subclass automatically has any constructor that the base class has.

The simplest way around this is for the base class to not declare a constructor (and thus have the default, no-arg constructor) or have a declared no-arg constructor (either by itself or alongside any other constructors). But often this approach can't be applied - because you need whatever arguments are being passed into the constructor to construct a legit instance of the class.

Java error: Implicit super constructor is undefined for default constructor

Solution

Problem