Constructors and Initialization

Duration: 5 min

What are Constructors?

A constructor is a special method that is called when an object is created. It initializes the object's attributes with initial values. Every class has at least one constructor - if you don't define one, Java provides a default constructor.

Types of Constructors

• Default Constructor: Takes no parameters, initializes attributes to default values
• Parameterized Constructor: Takes parameters to initialize attributes with specific values
• Constructor Overloading: Multiple constructors with different parameters

public class Student {
    private String name;
    private int rollNumber;
    private double gpa;
    
    // Default constructor
    public Student() {
        this.name = "Unknown";
        this.rollNumber = 0;
        this.gpa = 0.0;
    }
    
    // Parameterized constructor
    public Student(String name, int rollNumber) {
        this.name = name;
        this.rollNumber = rollNumber;
        this.gpa = 0.0;
    }
    
    // Constructor with all parameters
    public Student(String name, int rollNumber, double gpa) {
        this.name = name;
        this.rollNumber = rollNumber;
        this.gpa = gpa;
    }
    
    public void displayInfo() {
        System.out.println("Name: " + name + ", Roll: " + rollNumber + ", GPA: " + gpa);
    }
}

No output - this is a class definition

public class StudentDemo {
    public static void main(String[] args) {
        // Using default constructor
        Student s1 = new Student();
        s1.displayInfo();
        
        // Using parameterized constructor
        Student s2 = new Student("Alice", 101);
        s2.displayInfo();
        
        // Using constructor with all parameters
        Student s3 = new Student("Bob", 102, 3.8);
        s3.displayInfo();
    }
}

Name: Unknown, Roll: 0, GPA: 0.0
Name: Alice, Roll: 101, GPA: 0.0
Name: Bob, Roll: 102, GPA: 3.8

The this Keyword

The 'this' keyword refers to the current object. It's used to:
• Distinguish between instance variables and parameters with the same name
• Call other constructors in the same class
• Return the current object

public class ThisExample {
    private String name;
    private int age;
    
    // Constructor using 'this'
    public ThisExample(String name, int age) {
        this.name = name;  // 'this.name' refers to instance variable
        this.age = age;    // 'this.age' refers to instance variable
    }
    
    public void display() {
        System.out.println("Name: " + this.name + ", Age: " + this.age);
    }
}

No output - this is a class definition

💡 Tip: Constructor overloading allows you to create objects in different ways. Choose the constructor that best fits your needs.

Learn more: https://docs.oracle.com/javase/tutorial/java/javaOO/constructors.html

💡 Tip: Pro Tip: Master Constructors and Initialization thoroughly. This foundation is crucial for writing professional Java code.