Java compilation and execution flow - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare the main method in Java.

Java

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

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

Amain

Bexecute

Crun

Dstart

Attempts:

3 left

💡 Hint

Common Mistakes

Using a method name other than 'main' for the entry point.

Forgetting the exact signature of the main method.

The main method in Java must be named main to be the entry point of the program.

2fill in blank

medium

Complete the command to compile a Java file named Main.java.

Java

javac [1]

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

AMain.class

BMain

CMain.java

Dmain.java

Attempts:

3 left

💡 Hint

Common Mistakes

Trying to compile a .class file instead of a .java file.

Using wrong capitalization in the filename.

The javac command compiles Java source files with the .java extension.

3fill in blank

hard

Fix the error in the command to run the compiled Java program named Main.

Java

java [1]

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

AMain.java

BMain

CMain.class

Dmain

Attempts:

3 left

💡 Hint

Common Mistakes

Including the .class or .java extension when running the program.

Using lowercase 'main' instead of 'Main' if the class is named Main.

The java command runs the Java class by its class name without the .class extension.

4fill in blank

hard

Fill both blanks to complete the Java compilation and execution commands for a file named App.java.

Java

javac [1]
java [2]

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

AApp.java

Bapp

CApp

DApp.class

Attempts:

3 left

💡 Hint

Common Mistakes

Using the class file name in the compile command.

Using lowercase or incorrect class name in the run command.

To compile, use the source file App.java. To run, use the class name App without extension.

5fill in blank

hard

Fill all three blanks to complete the Java program structure and commands for a class named Demo.

Java

public class [1] {
    public static void [2](String[] args) {
        System.out.println("Demo program");
    }
}

// Compile with: javac [3]

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

ADemo

Bmain

CDemo.java

Ddemo

Attempts:

3 left

💡 Hint

Common Mistakes

Mismatching class name and file name.

Using incorrect method name for main.

Wrong capitalization in file name.

The class name is Demo. The main method is named main. The source file is Demo.java.

Practice

1. What is the first step when running a Java program?

easy

A. Compile the Java source code into bytecode using javac

B. Run the bytecode directly using the java command

C. Convert bytecode into machine code manually

D. Write the Java source code in a text editor

Solution

1. Step 1: Understand Java program execution

   Java source code must first be compiled into bytecode before running.

2. Step 2: Identify the compilation command

   The javac command compiles source code into bytecode.

3. Final Answer:

   Compile the Java source code into bytecode using javac -> Option A

4. Quick Check:

   Compilation = javac [OK]

Hint: Remember: javac compiles, java runs bytecode [OK]

Common Mistakes:

• Thinking java command compiles code
• Confusing source code with bytecode
• Skipping compilation step

2. Which command correctly runs a compiled Java program named HelloWorld?

easy

A. javac HelloWorld.java

B. java HelloWorld

C. java HelloWorld.java

D. javac HelloWorld

Solution

1. Step 1: Identify the command to run bytecode

   The java command runs compiled bytecode, not source files.

2. Step 2: Match the correct syntax

   Use java HelloWorld without the .java extension to run the program.

3. Final Answer:

   java HelloWorld -> Option B

4. Quick Check:

   Run bytecode = java ClassName [OK]

Hint: Run with java ClassName, no .java extension [OK]

Common Mistakes:

• Trying to run source file with java command
• Using javac to run program
• Including .java extension when running

3. Given the commands below, what will be the output?

javac Test.java
java Test

Assuming Test.java contains:

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

medium

A. Compilation error

B. Runtime error

C. Hello Java

D. No output

Solution

1. Step 1: Compile the source code

   javac Test.java compiles the code into bytecode without errors.

2. Step 2: Run the compiled bytecode

   java Test runs the program and prints "Hello Java".

3. Final Answer:

   Hello Java -> Option C

4. Quick Check:

   javac + java = program output [OK]

Hint: Compile first, then run to see output [OK]

Common Mistakes:

• Expecting output without compiling
• Confusing compilation and runtime errors
• Not including main method

4. What is wrong with this sequence of commands?

java HelloWorld
javac HelloWorld.java

medium

A. Running before compiling causes an error

B. javac should be run after java

C. Commands are correct and will work

D. HelloWorld.java file is missing

Solution

1. Step 1: Understand command order

   You must compile source code before running it.

2. Step 2: Identify error cause

   Running java HelloWorld before compiling causes a runtime error because bytecode is missing.

3. Final Answer:

   Running before compiling causes an error -> Option A

4. Quick Check:

   Compile first, then run [OK]

Hint: Always compile before running Java programs [OK]

Common Mistakes:

• Running java command before javac
• Assuming java compiles automatically
• Ignoring missing .class files

5. You have a Java source file App.java that depends on another class Helper.java. Which sequence correctly compiles and runs the program?

hard

A. javac App.java
java Helper
java App

B. java App
javac Helper.java
javac App.java

C. javac App.java Helper.java
java Helper

D. javac Helper.java
javac App.java
java App

Solution

1. Step 1: Compile dependencies first

   Compile Helper.java before App.java because App depends on Helper.

2. Step 2: Run the main program

   After compiling both, run java App to execute the program.

3. Final Answer:

   javac Helper.java javac App.java java App -> Option D

4. Quick Check:

   Compile dependencies first, then run main [OK]

Hint: Compile dependencies before main class, then run main [OK]

Common Mistakes:

• Running before compiling
• Compiling only main class
• Running wrong class with java command