Java Programmer Skills Programme

3.1 Lesson Outcomes

After completing this lesson, learners will be able to:

Create Java classes correctly.
Write Java source code.
Compile Java programs.
Execute Java applications.
Interpret program output.

3.2 Overview

Java applications are built using classes that contain methods, variables, and program logic. Developers create Java source files, compile them into bytecode, and execute them using the Java Virtual Machine (JVM).

This lesson introduces learners to the practical process of creating and running Java classes using Java development tools.

Creating and running Java classes is important in:

software development,
enterprise programming,
Java application development,
and object-oriented programming.

Understanding Java class creation and execution is important because it forms the foundation of Java software development.

PA0401 — Creating a Java Class

A Java class is a blueprint that contains program instructions and methods.

Example Java Class

Java

public class Main {

}

Rules for Java Class Creation

Rule	Description
File name matches class name	Main.java
Use class keyword	Defines class
Use braces	Defines class body

Practical Activity

Learners must:

create a Java class,
save the file correctly,
and apply Java naming conventions.

PA0402 — Writing the main() Method

The:

Plain text

main()

method is the entry point of a Java application.

Example

Java

public static void main(String[] args) {

System.out.println(“Hello Java”);
}

Components of main() Method

Component	Purpose
public	Access modifier
static	Shared method
void	No return value
main	Method name
String[] args	Command-line arguments

Practical Activity

Learners must:

create the main() method,
type Java statements,
and save the program.

PA0403 — Compiling Java Source Code

Compilation converts Java source code into bytecode.

Compilation Command

Plain text

javac Main.java

Result of Compilation

Plain text

Main.class

Practical Activity

Learners must:

open Command Prompt,
compile Java source files,
and identify generated class files.

PA0404 — Running Java Programs

Compiled Java applications are executed using the JVM.

Execution Command

Plain text

java Main

Example Output

Plain text

Hello Java

Practical Activity

Learners must:

execute Java programs,
observe console output,
and identify execution errors.

PA0405 — Modifying and Re-running Java Programs

Java programs can be edited, recompiled, and executed repeatedly.

Example Modified Program

Java

public class Main {

public static void main(String[] args) {

System.out.println(“Welcome to Java Programming”);
}
}

Practical Activity

Learners must:

modify Java source code,
save changes,
recompile programs,
and run updated applications.

PA0406 — Identifying Compilation and Runtime Errors

Errors may occur during compilation or execution.

Common Error Types

Error Type	Description
Syntax Error	Incorrect program structure
Runtime Error	Error during execution
Logical Error	Incorrect output

Practical Activity

Learners must:

identify compilation errors,
correct syntax mistakes,
and re-run programs successfully.

3.5 Key Notes / Summary

Java programs are created using classes.
The main() method is the program entry point.
javac compiles Java source files.
java executes compiled applications.
Java programs can be modified and recompiled.
Compilation and runtime errors must be corrected.