Constructors

1. What is a Constructor?

A constructor is a special block of code, similar to a method, that runs automatically when an object is created. It's typically used to set up initial values for an object's fields.

2. Why is it used?

Without a constructor, you'd need to manually set every field's value right after creating each object. A constructor lets you set these initial values automatically, right at the moment of creation.

3. Real-Life Example

Think of filling out basic details (name, date) the moment you open a new notebook for the first time, before writing anything else in it. A constructor performs this same kind of initial setup automatically, the moment an object is created.

4. Syntax

java
class ClassName {
    ClassName() {
        // constructor code, runs when object is created
    }
}

5. Example Program

java
class Student {
    String name;

    Student(String studentName) {
        name = studentName;
    }
}

public class ConstructorDemo {
    public static void main(String[] args) {
        Student s = new Student("Rohan");
        System.out.println("Student name: " + s.name);
    }
}

Output:

Student name: Rohan

6. Key Points to Remember

• A constructor has the same name as the class and no return type, not even void.
• If you don't write any constructor, Java automatically provides an empty default constructor.
• A class can have multiple constructors with different parameters — this is called constructor overloading.