Polymorphism in Java

 

What is Polymorphism?

Polymorphism means “many forms.”
In Java, it allows one object to take many forms — like a parent type being used to refer to child objects.

👉 It makes your code flexible, reusable, and extensible.

Types of Polymorphism

1. Compile-Time Polymorphism (Method Overloading)

2. Run-Time Polymorphism (Method Overriding)

1. Compile-Time Polymorphism – Method Overloading

Same method name, different parameters (in same class).

class MathUtils {

    int add(int a, int b) {

        return a + b;

    }

    double add(double a, double b) {

        return a + b;

    }

}

 2. Run-Time Polymorphism – Method Overriding

A child class redefines a method from its parent.

Example:

class Animal {

    void makeSound() {

        System.out.println("Some sound");

    }

}

class Dog extends Animal {

    void makeSound() {

        System.out.println("Bark");

    }

}

Animal a = new Dog();

a.makeSound();  // Output: Bark

interface vs abstract class in Java – What’s the Real Difference?

 In Object-Oriented Programming, both interfaces and abstract classes help you design flexible, reusable code.

But they’re not the same. Let’s break down the difference in a clean and simple way

What is an Interface?

• A pure blueprint - it can only contain:
• Method signatures (no body)
• final static constants
• Cannot have Constructors

Example:

interface Animal 

{

    void makeSound();

}

 What is an abstract class?

• A class that can have both abstract and non-abstract methods.

• Can have fields, constructors, and full method bodies.

• Cannot be directly instantiated.

.equals() vs == in Java – What’s the Real Difference?

 

In Java, you might think == and .equals() do the same thing — but they don’t.

Let’s break down the difference in a super simple way 👇

== Operator

• Compares references (memory addresses).

• Checks if two variables point to the same object in memory.
  Example:
  

  String a = new String("Java");

  String b = new String("Java");

  
  

  System.out.println(a == b);  // false ❌
  
  

  .equals() Method

  • Compares the actual content (data inside the object).

  • Works for objects like String, ArrayList, etc.

Difference Between Array and ArrayList in Java

 Both Array and ArrayList are used to store multiple values in Java — but they work a little differently.

Let’s look at what makes them different, and when to use each one.

Array

• Fixed size (you can’t change it once created)

• Can store primitive types like int, double, etc.

• Syntax:
  

  int[] numbers = new int[5];

  numbers[0] = 10;
  
  
  ArrayList
  

• Can grow and shrink in size

• Only works with objects, not primitives (use Integer instead of int)

• Comes from java.util.ArrayList

• Syntax:
  

  import java.util.ArrayList;

  ArrayList<Integer> numbers = new ArrayList<>();

  numbers.add(10);

What’s the Difference Between break and continue in Java?

In loops, sometimes you want to stop everything or skip just one step. That’s where break and continue come in.

Let’s break it down 👇

🛑 break

• Completely exits the loop.

• Often used when a certain condition is met and you don’t want to keep looping.

Example:

for (int i = 1; i <= 10; i++) {

    if (i == 5) {

        break;  // Loop ends here

    }

    System.out.print(i + " ");

}

// Output: 1 2 3 4

⏭️ continue

• Skips just the current step, but keeps looping.

• Useful when you want to skip a specific case.

Example:

for (int i = 1; i <= 5; i++) {

    if (i == 3) {

        continue;  // Skip 3, but keep looping

    }

    System.out.print(i + " ");

}

// Output: 1 2 4 5

Key Difference

Keyword	What it does
break	Stops the entire loop
continue	Skips current step, goes to next

 

What’s the Difference Between for Loop and while Loop in Java?

 Loops are a big part of Java — they help us repeat things. But many beginners get confused between for loops and while loops.

So here’s a quick breakdown of how they’re different and when to use each one.

for Loop

• Used when you know how many times you want to loop.

• Syntax:
  

  for (int i = 0; i < 5; i++) {

      System.out.println("Hello!");

  }

• Best for counting or looping a fixed number of times.
  

  while Loop

  • Used when you don’t know how many times you’ll need to loop — but you keep looping until a condition is false.

  • Syntax:
    

    boolean t = true;
    int i = 0;
    while(t)
    {
    

    i++;

    } 

  • Best for things like waiting for a user input or looping until a goal is reached.
    
    

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