📘LESSON 5

3.1 Lesson Outcomes

After completing this lesson, learners will be able to:

• Explain the Java platform.
• Differentiate between Java, Javac, and Bytecode.
• Define Java classes and objects.
• Differentiate between JDK, JRE, and JVM.
• Explain the role of JVM in Java program execution.

3.2 Overview

The Java platform provides the environment required to develop, compile, and execute Java applications. Java programs follow a unique compilation process where source code is converted into bytecode before execution by the Java Virtual Machine (JVM).

This lesson introduces learners to the Java platform and explains the relationship between Java source code, bytecode, classes, objects, JDK, JRE, and JVM.

The Java platform is widely used in:

• enterprise systems,
• web applications,
• Android development,
• cloud computing,
• and software engineering.

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

KT0501 — Overview of Java Platform – An Introduction – Java, Javac, Bytecode

The Java platform provides the tools and environment needed to:

• write Java programs,
• compile Java code,
• and execute Java applications.

Java

Java is a high-level programming language used to create software applications.

Javac

javac

is the Java compiler used to convert Java source code into bytecode.

Bytecode

Bytecode is an intermediate code generated after compilation.

Bytecode is executed by the:

Java Virtual Machine (JVM)

Java Compilation Process

Example Java Source Code

public class Main {

    public static void main(String[] args) {

        System.out.println("Hello World");
    }
}

Compilation Command

javac Main.java

Execution Command

java Main

Importance of Java Platform

The Java platform supports:

• cross-platform compatibility,
• software execution,
• and enterprise application development.

KT0502 — Java Class and Object

A class is a blueprint used to create objects.

An object is an instance of a class.

Class Example

public class Student {

    String name;
    int age;
}

Object Example

public class Main {

    public static void main(String[] args) {

        Student student1 = new Student();

        student1.name = "John";

        student1.age = 20;

        System.out.println(student1.name);
    }
}

Output

John

Importance of Classes and Objects

Classes and objects support:

• object-oriented programming,
• reusable code,
• and software organization.

KT0503 — JDK vs JRE vs JVM

The Java platform contains several important components used during development and execution.

JDK — Java Development Kit

The JDK is a software development kit used to:

• write programs,
• compile source code,
• and develop Java applications.

The JDK includes:

• compiler tools,
• libraries,
• and development utilities.

JRE — Java Runtime Environment

The JRE is a software bundle that allows Java programs to run.

The JRE contains:

• JVM,
• libraries,
• and runtime support files.

JVM — Java Virtual Machine

The JVM is an environment used to execute Java bytecode.

The JVM:

• converts bytecode into machine-level instructions,
• manages memory,
• and executes Java applications.

Comparison of Components

Relationship Between JDK, JRE and JVM

JDK → JRE → JVM

Importance of Java Platform Components

These components support:

• Java development,
• compilation,
• portability,
• and software execution.

3.5 Key Notes / Summary

• The Java platform supports Java application development and execution.
• Java programs are compiled using javac.
• Bytecode is executed by the JVM.
• A class is a blueprint for creating objects.
• Objects are instances of classes.
• JDK supports software development.
• JRE provides runtime support.
• JVM executes Java bytecode.