Introduction to Programming

Widening

For example, if a class, SomeClass, extends SomeBaseClass, the following declaration and initialization are possible:

SomeBaseClass someBaseClass = new SomeBaseClass();someBaseClass = new SomeClass();

And, since every class extends the java.lang.Object class by default, the following declarations and initializations are possible too:

Object someBaseClass = new SomeBaseClass();someBaseClass = new SomeClass();             //line 2

In line 2, we assigned a subclass instance reference to a variable of a superclass type. Methods present in a subclass but not in the superclass are not accessible via the reference of the superclass type. The assignment in line 2 is called a widening of the reference because it becomes less specialized.