Constructors in abstract classes? [duplicate]

Answer 1

because an class that inherits your abstact class can call this constructor

abstract class Foo {

    private int number;

    public Foo(int i) {
        this.number = i;
    }
}

class Bar extends Foo {

    public Bar() {
        super(1);
    }

}

Answer 2

Subclasses can be instantiated and can call the abstract class's constructor from its constructor. Example:

abstract class Foo
{
  public Foo()
  {
    // Do Stuff
  }
}

class Bar extends Foo
{
  public Bar()
  {
    super();
  }
}

Answer 3

The abstract constructor forces classes that inherit from the class to implement (or call) the constructor. This implies that you can be sure that any operations in the constructor of the abstract class will be executed.