Composition of "Is-A" and “Has-A” Relationship in JAVA

Java programming: “IS A” and “Has A”
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“IS A”
Hierarchical inheritance is a mechanism where two or more sub-classes acquire properties from similar super class. The relationship “IS A” is simply a parent to child relationship (Gosling, Holmes & Arnold, 2005). Below is a Java code segment demonstrating a three level “IS A” hierarchical relationship.
// Java program to illustrate the
// concept of a three level "IS A" Hierarchical //inheritance
class Animal{
public void sleep() {
System.out.println("is sleeping ");
}
}
class Sheep extends Animal {
public void baa() {
System.out.println("is baasing");
}
}
class Dog extends Animal {
public void barks() {
System.out.println("is barking");
}
}
class Lion extends Animal {
public void grunts() {
System.out.println("is grunting");
}
}
// Here is the driver class
public class All {
public static void main(String[] args)
{
//creating an object of class sheep
//and calling the inherited method and //its newly created method
Sheep s1 = new Sheep();
s1.baa();
s1.sleep();
}
}
Descriptions of the above program
The program is made up of one superclass which is class Animal. The superclass is then inherited by three more classes which are class Dog, class Sheep and class Lion. All these classes have acquired the method described in class Animal. Since the superclass Animal has the method sleep (), all its subclasses inherit it in their operations. This demonstrates a three-level hierarchical inheritance since three subclasses...