What is Java - Practice Questions & Exercises

Challenge - 5 Problems

🧠 Conceptual

intermediate

What is Java primarily used for?

Java is a popular programming language. What is its main use?

A Creating mobile apps, web applications, and large systems

B Only for designing websites with HTML and CSS

C Writing scripts to automate Excel spreadsheets

D Building hardware devices and microchips

💡 Hint

Think about where you see Java programs running, like apps or websites.

Java is widely used to build mobile apps (especially Android), web applications, and large software systems because it is versatile and runs on many devices.

❓ Predict Output

intermediate

What is the output of this Java code?

Look at this Java program and choose the output it produces when run.

Java

public class Main {
    public static void main(String[] args) {
        int x = 5;
        int y = 10;
        System.out.println("Sum is: " + (x + y));
    }
}

A Sum is: 15

B Sum is: 510

C Sum is: x + y

D Sum is: 5 + 10

💡 Hint

Remember that parentheses change how expressions are calculated in Java.

The parentheses around (x + y) make Java add the numbers first, then convert to string. So it prints "Sum is: 15".

❓ Predict Output

advanced

What does this Java code print?

Analyze the code and select the exact output it produces.

Java

public class Main {
    public static void main(String[] args) {
        String s = "Java";
        s += 123;
        System.out.println(s);
    }
}

A Java 123

B Java123

C Java+123

D Error: cannot add int to String

💡 Hint

In Java, adding a number to a string converts the number to text.

Using += with a string and a number converts the number to string and joins them. So "Java" + 123 becomes "Java123".

🔧 Debug

advanced

What error does this Java code cause?

Look at this Java code and choose the error it produces when compiled.

Java

public class Main {
    public static void main(String[] args) {
        int number = "100";
        System.out.println(number);
    }
}

A Syntax error: missing semicolon

B Variable number might not have been initialized

C Type mismatch: cannot convert from String to int

D No error, prints 100

💡 Hint

Check the type of the value assigned to an int variable.

You cannot assign a text (String) value to an int variable directly. This causes a type mismatch error.

🧠 Conceptual

expert

Which feature makes Java platform-independent?

Java is called platform-independent. What feature allows this?

A Java programs must be rewritten for each operating system

B Java programs are written in machine code for each platform

C Java uses HTML to run in browsers

D Java Virtual Machine (JVM) that runs bytecode on any device

💡 Hint

Think about how Java runs the same program on different computers without changes.

Java compiles code into bytecode, which the JVM interprets on any device, making it platform-independent.