🚀 Java Constructors – Masterclass with Examples

constructors:

• ✅ Basic explanation
• 🤔 Why we use constructors
• 📌 Types of constructors
• 💭 Real-life examples
• 🧠 Most asked constructor-based interview questions (with answers)
• 🧪 Puzzles and tricky constructor questions for practice

🚀 Java Constructors – Masterclass with Examples

✅ What is a Constructor?

A constructor is a special method in a class:

• It has the same name as the class
• It has no return type (not even void)
• It runs automatically when an object is created

🤔 Why Do We Use Constructors?

• To initialize objects
• To assign default or custom values
• To run specific logic when an object is created

📌 Types of Constructors in Java

💡 Example:

public class Student { String name; int age; // Constructor Student(String n, int a) { name = n; age = a; } void display() { System.out.println(name + " - " + age); } public static void main(String[] args) { Student s1 = new Student("Arun", 21); s1.display(); } } 

🧠 Top Java Constructor Interview Questions with Answers

Q1: Can a constructor be overloaded?

✅ Yes! Just like methods, you can create multiple constructors with different parameter lists.

public class Person { Person() { System.out.println("No-arg"); } Person(String name) { System.out.println("Name: " + name); } } 

Q2: What happens if you don't write a constructor?

✅ Java provides a default constructor (no-args) automatically.

But if you write any constructor, Java won’t generate the default one.

Q3: Can constructors be private?

✅ Yes. Used in Singleton Design Pattern to restrict object creation.

private ConstructorExample() { // Cannot create from outside } 

Q4: Is it possible to call a constructor from another constructor?

✅ Yes, using this() keyword.

Student() { this("Default Name"); } Student(String name) { System.out.println(name); } 

Q5: Can constructors be inherited?

❌ No. Constructors are not inherited, but the subclass can call the superclass constructor using super().

🔍 Tricky Constructor Puzzle Questions

🔸 Puzzle 1:

class Test { Test() { System.out.println("Constructor"); } void Test() { System.out.println("This is a method"); } public static void main(String[] args) { Test t = new Test(); t.Test(); } } 

✅ Output:

Constructor This is a method 

📌 Why? Because method name can be same as class name, but it still acts like a method due to return type.

🔸 Puzzle 2:

class Demo { Demo() { this(10); System.out.println("Default"); } Demo(int x) { System.out.println("Parameterized: " + x); } public static void main(String[] args) { new Demo(); } } 

✅ Output:

Parameterized: 10 Default 

🔸 Puzzle 3:

class A { A() { System.out.println("A constructor"); } } class B extends A { B() { System.out.println("B constructor"); } } public class Main { public static void main(String[] args) { new B(); } } 

✅ Output:

A constructor B constructor 

📌 Reason: Super constructor is always called first.

✨ Summary