Static variables in Java - Mini Project: Build & Apply

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Understanding Static Variables in Java

📖 Scenario: You are creating a simple program to track how many objects of a class have been created. This is useful in many real-world situations, like counting how many users have signed up or how many products are in stock.

🎯 Goal: Build a Java program that uses a static variable to count the number of instances created from a class called Counter. You will see how static variables keep a shared value for all objects.

📋 What You'll Learn

Create a class named Counter with a static variable count initialized to 0

Add a constructor in Counter that increases count by 1 each time an object is created

Create three objects of the Counter class

Print the value of the static variable count to show how many objects were created

💡 Why This Matters

🌍 Real World

Counting how many instances of a class exist is useful in resource management, like tracking active users or open connections.

💼 Career

Understanding static variables is important for Java developers to manage shared data and memory efficiently.

1

Create the Counter class with a static variable

Create a class called Counter with a static int count variable initialized to 0.

Java

class Counter {
    // Your code here
}

💡 Need a hint?

Remember, static means the variable belongs to the class, not to any single object.

2

Add a constructor to increase the count

Add a constructor to the Counter class that increases the count variable by 1 each time a new object is created.

Java

class Counter {
    static int count = 0;

    // Your code here
}

💡 Need a hint?

The constructor has the same name as the class and no return type.

3

Create three Counter objects

In the main method, create three objects of the Counter class named c1, c2, and c3.

Java

class Counter {
    static int count = 0;

    Counter() {
        count++;
    }
}

public class Main {
    public static void main(String[] args) {
        // Create three Counter objects here
        // Your code here
    }
}

💡 Need a hint?

Use the new keyword to create objects.

4

Print the total count of Counter objects

Add a System.out.println statement in the main method to print the value of Counter.count.

Java

class Counter {
    static int count = 0;

    Counter() {
        count++;
    }
}

public class Main {
    public static void main(String[] args) {
        Counter c1 = new Counter();
        Counter c2 = new Counter();
        Counter c3 = new Counter();

        // Print the count here
        // Your code here
    }
}

💡 Need a hint?

Access the static variable using the class name, not the object.