Inheritance hierarchy: The relationship among super-classes and sub-classes is termed as an inheritance hierarchy. The single inheritance of classes means that each and every class has simply a single `parent' class and that Object class is the eventual ancestor of all classes - at the peak of the hierarchy. Two classes which have similar immediate super-class can be thought of as sibling sub classes. Multiple inheritance of interfaces provides the hierarchy a more complicated structure than that of resultant from simple class inheritance.