How is an abstract class different from an interface?
Ans : Although the Java language makes a clear distinction between abstract classes and interfaces, in practice the difference is often a matter of degree and intent. Abstract classes fill in the wide range between concrete classes and interfaces. Table 1.5 lists several distinctions that are relevant to typical uses. Table 1.5: Concrete Class versus Abstract Class versus Interface Concrete Class Abstract Class Interface specifies the full set of methods for an object specifies the full set of methods for an object specifies a subset of methods for an object implements all of its methods implements none, some, or all of its methods implements none of its methods can have instances can’t have instances can’t have instances can have subclasses must have subclasses; useless without them can’t have subclasses; must have classes that implement it; useless without them If the differences in Table 1.5 leave you uncertain about whether to use an abstract class or an interface, one further fact
