Writing first Java program - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to print "Hello, World!" to the console.

Java

public class HelloWorld {
    public static void main(String[] args) {
        System.out.[1]("Hello, World!");
    }
}

Drag options to blanks, or click blank then click option'

Aprintln

Bprint

Cwrite

Doutput

Attempts:

3 left

💡 Hint

Common Mistakes

Using print instead of println may not add a new line after output.

The println method prints the text and moves to a new line, which is the standard way to output text in Java.

2fill in blank

medium

Complete the code to declare the main method correctly.

Java

public class Main {
    public static void [1](String[] args) {
        System.out.println("Welcome!");
    }
}

Drag options to blanks, or click blank then click option'

Aexecute

Bmain

Crun

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Using other method names like start or run will not run the program automatically.

The main method must be named main for the Java program to start execution there.

3fill in blank

hard

Fix the error in the class declaration to make it valid Java code.

Java

public [1] HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hi!");
    }
}

Drag options to blanks, or click blank then click option'

Aclass

BClass

Cmethod

Dfunction

Attempts:

3 left

💡 Hint

Common Mistakes

Using uppercase Class causes a syntax error.

The keyword to declare a class in Java is class in lowercase.

4fill in blank

hard

Fill both blanks to complete the program that prints a greeting.

Java

public [1] Greeting {
    public static void main(String[] [2]) {
        System.out.println("Hello!");
    }
}

Drag options to blanks, or click blank then click option'

Aclass

Bargs

Cargv

DClass

Attempts:

3 left

💡 Hint

Common Mistakes

Using uppercase Class or argv instead of args.

The class declaration uses class and the main method parameter is usually named args.

5fill in blank

hard

Fill all three blanks to complete the Java program that prints a message.

Java

public [1] MessagePrinter {
    public static void main(String[] [2]) {
        System.out.[3]("Message printed!");
    }
}

Drag options to blanks, or click blank then click option'

Aclass

Bargs

Cprintln

DClass

Attempts:

3 left

💡 Hint

Common Mistakes

Using uppercase Class, argv, or print instead of println.

The class keyword is class, the main method parameter is args, and the print method is println.

Practice

1. What is the purpose of the main method in a Java program?

easy

A. It is the starting point where the program begins execution.

B. It defines a new class in Java.

C. It is used to declare variables.

D. It imports external libraries.

Solution

1. Step 1: Understand the role of the main method

   The main method is special because Java looks for it to start running the program.

2. Step 2: Identify the program entry point

   Without the main method, the program has no defined starting point to execute code.

3. Final Answer:

   It is the starting point where the program begins execution. -> Option A

4. Quick Check:

   Main method = program start [OK]

Hint: Remember: Java runs code starting from main method [OK]

Common Mistakes:

• Thinking main defines a class
• Confusing main with variable declaration
• Assuming main imports libraries

2. Which of the following is the correct syntax to print "Hello, World!" with a newline in Java?

easy

A. System.out.print("Hello, World!");

B. print("Hello, World!");

C. System.out.println("Hello, World!");

D. echo "Hello, World!";

Solution

1. Step 1: Identify the correct print method in Java

   Java uses System.out.println() to print text with a new line.

2. Step 2: Check each option for syntax correctness

   System.out.print("Hello, World!"); uses print which prints without a new line, but is valid. System.out.println("Hello, World!"); uses println which prints with a new line and is the common way. print("Hello, World!"); and D are not valid Java syntax.

3. Final Answer:

   System.out.println("Hello, World!"); -> Option C

4. Quick Check:

   Print line = System.out.println() [OK]

Hint: Use System.out.println() to print with a new line [OK]

Common Mistakes:

• Using print without System.out
• Using non-Java print commands
• Missing quotes around text

3. What will be the output of the following Java program?

public class Hello {
    public static void main(String[] args) {
        System.out.println("Welcome to Java!");
    }
}

medium

A. Syntax Error

B. Hello

C. Welcome to Java!\n

D. Welcome to Java!

Solution

1. Step 1: Read the print statement inside main

   The program prints the exact string "Welcome to Java!" using System.out.println.

2. Step 2: Understand println adds a new line but does not show \n literally

   The output shows the text and moves to the next line, but the new line is not visible as characters.

3. Final Answer:

   Welcome to Java! -> Option D

4. Quick Check:

   Print output = Welcome to Java! [OK]

Hint: System.out.println prints text exactly as given [OK]

Common Mistakes:

• Confusing output with class name
• Expecting \n characters in output
• Assuming syntax error without reason

4. Identify the error in the following Java program:

public class Test {
    public static void main(String[] args) {
        System.out.println("Hello Java")
    }
}

medium

A. Class name should be lowercase.

B. Missing semicolon after the print statement.

C. main method should not have String[] args.

D. System.out.println should be System.print.

Solution

1. Step 1: Check syntax of print statement

   The print statement is missing a semicolon at the end, which is required in Java.

2. Step 2: Verify other parts for correctness

   Class name capitalization is allowed, main method signature is correct, and System.out.println is the right method.

3. Final Answer:

   Missing semicolon after the print statement. -> Option B

4. Quick Check:

   Semicolon missing = syntax error [OK]

Hint: Always end statements with a semicolon in Java [OK]

Common Mistakes:

• Omitting semicolon at line end
• Changing class name case unnecessarily
• Incorrect main method signature

5. You want to create a Java program that prints "Good Morning!". Which of the following is the correct file name and class name combination to run the program successfully?

hard

A. File name: GoodMorning.java, Class name: GoodMorning

B. File name: goodmorning.java, Class name: GoodMorning

C. File name: GoodMorning.java, Class name: goodmorning

D. File name: GoodMorning.txt, Class name: GoodMorning

Solution

1. Step 1: Understand Java file and class naming rules

   The file name must exactly match the public class name including case, with .java extension.

2. Step 2: Check each option for matching names and extension

   File name: GoodMorning.java, Class name: GoodMorning matches file and class names exactly with correct extension. Options B and C have case mismatches. File name: GoodMorning.txt, Class name: GoodMorning has wrong file extension.

3. Final Answer:

   File name: GoodMorning.java, Class name: GoodMorning -> Option A

4. Quick Check:

   File name = Class name + .java [OK]

Hint: Match file name exactly with class name and use .java extension [OK]

Common Mistakes:

• Mismatching class and file names
• Using wrong file extension
• Ignoring case sensitivity