Java Selenium TestNG CI/CD API Testing Database Playwright Performance

Chapter 3: Java Basics

Variables and Data Types

A variable stores a value that your program can use and change. In test automation, variables hold test data — URLs, usernames, expected values, element counts.

VariableBasics.javajava

public class VariableBasics {
    public static void main(String[] args) {
        String url = "https://demo-bank.example.com";
        String username = "testuser";
        int loginAttempts = 3;
        boolean isLoggedIn = false;

        System.out.println("Testing: " + url);
        System.out.println("User: " + username);
        System.out.println("Max attempts: " + loginAttempts);
        System.out.println("Logged in: " + isLoggedIn);
    }
}

Every variable has a type, a name, and a value. The type determines what kind of data it holds. Java is strongly typed — you cannot put text into an int variable.

Primitive Data Types

Java has 8 primitive types. In test automation, you primarily use four: int, double, boolean, and char. The rest (byte, short, long, float) are for specific cases.

Type	Stores	Size	Example	Automation Use
int	Whole numbers	4 bytes	42, -7, 0	Counts, indices, scores
double	Decimals	8 bytes	3.14, -0.5	Prices, percentages, duration
boolean	true/false	1 bit	true, false	Element visible, test passed
char	Single character	2 bytes	'A', '$', '7'	Rarely used directly
long	Large numbers	8 bytes	9999999999L	Timestamps, large IDs
float	Decimals (less precise)	4 bytes	3.14f	Rarely used — use double
byte	-128 to 127	1 byte	100	File handling
short	-32768 to 32767	2 bytes	30000	Rarely used

DataTypes.javajava

public class DataTypes {
    public static void main(String[] args) {
        int itemCount = 5;
        double price = 29.99;
        boolean inStock = true;
        char grade = 'A';
        long orderId = 1234567890L;
        String productName = "Laptop";

        System.out.println(productName + " | Qty: " + itemCount + " | Price: $" + price);
        System.out.println("In stock: " + inStock);
        System.out.println("Grade: " + grade);
        System.out.println("Order ID: " + orderId);
    }
}

String is NOT a primitive — it is a class (starts with uppercase S). Primitives start with lowercase (int, double, boolean). This distinction matters when comparing values.

Declaration, Initialization, Assignment

VarLifecycle.javajava

public class VarLifecycle {
    public static void main(String[] args) {
        // Declare — creates a variable with no value
        int retryCount;

        // Initialize — first value assignment
        retryCount = 3;

        // Reassign — change the value
        retryCount = 5;

        // Declare and initialize in one line (preferred)
        String browser = "Chrome";
        double timeout = 10.0;

        // Multiple variables of same type
        int x = 1, y = 2, z = 3;

        System.out.println("Retries: " + retryCount);
        System.out.println("Browser: " + browser);
    }
}

Using a variable before initializing it causes a compile error: variable retryCount might not have been initialized. Java does not assign default values to local variables.

Naming Conventions

camelCase for variables and methods: loginAttempts, isVisible, getPageTitle
PascalCase for classes: LoginPage, TestRunner, HomePage
UPPER_SNAKE_CASE for constants: MAX_RETRIES, BASE_URL, TIMEOUT
Names must start with a letter, underscore, or dollar sign — not a digit
Use meaningful names: elementCount not ec, isDisplayed not flag

Constants with final

The final keyword makes a variable a constant — its value cannot change after assignment. Use it for values that should never be modified during test execution.

Constants.javajava

public class Constants {
    public static void main(String[] args) {
        final String BASE_URL = "https://demo-bank.example.com";
        final int MAX_RETRIES = 3;
        final double TIMEOUT = 30.0;

        System.out.println("URL: " + BASE_URL);
        System.out.println("Max retries: " + MAX_RETRIES);

        // BASE_URL = "https://other-site.com";  // Compile error: cannot assign to final variable
    }
}

Q: What is the difference between int and Integer in Java?

A: int is a primitive type that stores a raw 32-bit number on the stack. Integer is a wrapper class — an object that contains an int value. Integer can be null (useful for database fields that might be empty), works with Collections (ArrayList<Integer>), and provides utility methods like Integer.parseInt(). Java auto-boxes between them: Integer x = 5 automatically wraps the int into an Integer object.

Q: What happens when you divide two integers in Java?

A: Java performs integer division — the decimal part is truncated, not rounded. 7 / 2 returns 3, not 3.5. To get a decimal result, at least one operand must be a double: 7.0 / 2 returns 3.5, or cast one side: (double) 7 / 2.

Try It Yourself

Exercise 1: Create variables for a test scenario — store a URL, username, password, expected page title, and timeout. Print all values in a readable format.

Exercise 2: Declare an int variable, print it, reassign it to a new value, and print again. Then try adding final and reassigning — what error do you get?

Exercise 3: What is the output? ``int a = 10; int b = 3; System.out.println(a / b); System.out.println((double) a / b);``

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