In Java, subclasses of a class (“superclass” relative to the subclass) inherit state and behavior, such as having access to all methods defined for the parent class.
Each class may have only one superclass “above” it in inheritance, but has no limit to the number of subclasses “below”.
Subclass delcaration syntax: class SubclassName extends SuperclassName {/*subclass code block*/}
In Java, an interface is a specified list of object behaviors.
Interface syntax:
interface ClassName {
void methodToImplementLater(int parameterName);
}
An implemented class must define each method declared in the interface.
Implementation syntax:
class ImplementedClassName implements ClassName
{
/*code block*/
void methodToImplementLater (int parameterName) {
/*method code block*/
}
A Java package is a grouping of related or otherwise interacting classes and interfaces.
The Application Programming Interface package for Java contains very many commonly used classes (Documentation Here)