Introduction

In Java, inheritance is commonly used to reuse code using the extends keyword. However, inheritance is not always the best solution. In many real-world applications, developers prefer a more flexible and maintainable approach called composition.

This article explains how to share data both with inheritance and without inheritance, using simple examples, a relatable story, and the role of access modifiers.

A Simple Story to Understand

Consider a School and Student relationship:

• A School does not become a Student
• A School has Students

This highlights the difference:

• Inheritance represents an IS-A relationship
• Composition represents a HAS-A relationship

Using Inheritance (IS-A Relationship)

Student.java

package shop;

public class Student {
    protected String name = "Vinay";

    public void showName() {
        System.out.println(name);
    }
}

School.java

package shop;

public class School extends Student {

    public static void main(String[] args) {
        School sc = new School();
        sc.showName();  // inherited method
    }
}

Explanation

• School extends Student, meaning School is treated as a Student
• This is not logically correct for this scenario
• protected allows access within subclasses

Using Composition (Without Inheritance)

Student.java

package shop;

public class Student {
    private String name = "Vinay";

    public String getName() {
        return name;
    }
}

School.java

package shop;

public class School {

    public void display(Student s) {
        System.out.println(s.getName());
    }
}

Main.java

package shop;

public class Main {

    public static void main(String[] args) {
        Student s = new Student();
        School sc = new School();

        sc.display(s);  // HAS-A relationship
    }
}

Role of Access Modifiers

Access modifiers control how data is accessed:

• private → accessible only within the same class
• protected → accessible in subclasses
• public → accessible everywhere

In composition:

• Data is kept private
• Access is provided through public getter methods

This improves data security and encapsulation.

Inheritance vs Composition

When to Use Each

Use inheritance when:

• There is a clear IS-A relationship
• Example: Dog is an Animal

Use composition when:

• There is a HAS-A relationship
• Example: School has Students

References

• https://docs.oracle.com/javase/tutorial/java/concepts/index.html
• https://www.w3schools.com/java/java_oop.asp
• https://www.geeksforgeeks.org/object-oriented-programming-oops-concept-in-java/
• https://www.geeksforgeeks.org/favoring-composition-over-inheritance-in-java-with-examples/