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Remember Things

Remember Things

Declare and use variables (int, double, boolean).

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Let’s teach your Java programs how to remember things. In this lesson, you’ll store values using variables, give them names, and reuse them whenever you need.

Goal

You’ll aim to:

  • Declare and assign variables.

  • Use types: int, double, boolean.

  • Print and reuse values.

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Variables in Java
Variables in Java

The illustration above shows a variable named age, assigned an integer value of 20, with a memory address of 0x5656.

Declare a variable

Time to assign an integer value to a variable and see what it prints:

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public class Main {
    public static void main(String[] args) {
        int age = 20;
        System.out.println("You are " + age + " years old.");
    }
}

int is used for whole numbers like 10, 20, or 100.

Great! You just created and printed your first variable.

More types

Let’s explore the double and boolean data types. A double stores decimal numbers, while a boolean holds either true or false.

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public class Main {
    public static void main(String[] args) {
        double price = 4.99;         // decimal
        boolean isSunny = true;      // true or false
        System.out.println("Price: $" + price);
        System.out.println("Sunny today? " + isSunny);
    }
}

In Java, you must always tell the computer what type of value a variable will store. This is called static typing.

Well done! You’ve successfully declared and initialized both a double and a boolean variable.

Reassign variables

Let’s reassign the integer value 21 to the age variable below.

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public class Main {
    public static void main(String[] args) {
        int age = 20;
        age = 21;
        System.out.println("Next year: " + age);
    }
}

You can change a variable’s value anytime—just assign a new one.

Well done! You’ve successfully reassigned the integer variable with the value 21.

Mini challenge

Make a program that stores:

  • Your height in feet (as a double)

  • Whether you like pizza (boolean)

  • A message that prints both together

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public class Main {
    public static void main(String[] args) {
        //Write your code here:
    }
}

If you’re stuck, click the “Show Solution” button.

You did it! Another challenge complete—nice work.

Variable types recap

  • int → whole numbers

  • double → decimals

  • boolean → true or false

  • String → text (coming next!)

What’s next?

Next up: how to store and work with text using String variables.