Default values in Java - Mini Project: Build & Apply

Default values

📖 Scenario: Imagine you are creating a simple Java program to understand how default values work for different types of variables in Java.

🎯 Goal: You will create a Java class with different types of variables and observe their default values when they are not explicitly initialized.

📋 What You'll Learn

Create a Java class named DefaultValuesDemo

Declare instance variables of types int, double, boolean, and String without initializing them

Create a method named printDefaults that prints the default values of these variables

Create a main method to create an object of DefaultValuesDemo and call printDefaults

💡 Why This Matters

🌍 Real World

Understanding default values helps avoid bugs caused by uninitialized variables in Java programs.

💼 Career

Java developers must know default values to write safe and predictable code, especially when working with classes and objects.

1

Create the class and declare variables

Create a public class named DefaultValuesDemo and declare four instance variables without initializing them: int number, double price, boolean available, and String name.

Java

public class DefaultValuesDemo {
    // Declare instance variables here
    // Your code here
}

Need a hint?

Instance variables in Java have default values if not initialized.

2

Add the printDefaults method

Inside the DefaultValuesDemo class, create a public method named printDefaults that prints the values of number, price, available, and name using System.out.println.

Java

public class DefaultValuesDemo {
    int number;
    double price;
    boolean available;
    String name;

    // Create printDefaults method here
    // Your code here
}

Need a hint?

Use System.out.println to print each variable with a label.

3

Add the main method

Inside the DefaultValuesDemo class, add a public static main method. Inside it, create an object of DefaultValuesDemo named demo and call the printDefaults method on it.

Java

public class DefaultValuesDemo {
    int number;
    double price;
    boolean available;
    String name;

    public void printDefaults() {
        System.out.println("number = " + number);
        System.out.println("price = " + price);
        System.out.println("available = " + available);
        System.out.println("name = " + name);
    }

    // Create main method here
    // Your code here
}

Need a hint?

The main method is the program entry point. Create an object and call the method.

4

Run and observe the output

Run the program and observe the output printed by the printDefaults method. The output should show the default values of the variables.

Java

public class DefaultValuesDemo {
    int number;
    double price;
    boolean available;
    String name;

    public void printDefaults() {
        System.out.println("number = " + number);
        System.out.println("price = " + price);
        System.out.println("available = " + available);
        System.out.println("name = " + name);
    }

    public static void main(String[] args) {
        DefaultValuesDemo demo = new DefaultValuesDemo();
        demo.printDefaults();
    }
}

// Run the program to see the output

Need a hint?

Default values for instance variables are 0 for int, 0.0 for double, false for boolean, and null for String.