Java Day 00

What is
Java?

▫ General-purpose

computer-programming
language

▫ Concurrent, class-based,

object-oriented

▫ … and minimum

implementation of
dependencies as possible

Java bytecode is the

instruction set of the Java

virtual machine

Features

▫ No pointers
▫ Automatic garbage collection
▫ rich pre-defined class library
▫ All functions are associated

with objects

▫ Potentially better code

organization and reuse

▫ Platform independent
▫ Java bytecode can run on any

JVM, on any platform

JVM
Steps:

▫ Source code is in plain text files

ending with the .java extension

▫ Compile those source files into

.class files by the javac compiler

▫ A .class file contains bytecodes —

the machine language of the Java
Virtual Machine (Java VM)

▫ Run the bytecode/.class file using

JVM

Java
Virtual
Machine
(JVM)

Because the Java VM is
available on many different
operating systems, the same
.class files are capable of
running on any platform.

Difference
between
JDK and
JRE?

JRE:

If you want to run Java programs, but
not develop them, download the JRE.

JDK:

If you want to develop Java
applications, download the Java
Development Kit, or JDK.

The JDK includes the JRE, so you do
not have to download both
separately.

Download

Java JDK -
https://drive.google.com/file
/d/1hGjA0f5OvTL4tpp6hzflN
PTceQQmb0Ns/view?usp=sh
aring

Download

DrJava -
https://drive.google.com/file
/d/1ANTDnN-w_TWSGpS3N
VJ6O920xkX3z_dS/view?usp
=sharing

VS Code

Our IDE - Dr. Java

IDE = Integrated
Development Environment

Writing,
Compiling,
Running

STEP1: Write and save your program in
Dr Java such as HelloWorld.java

STEP2: Compile the source file into a
.class file

STEP3: Run the program

☕

Java programs are called
‘classes’

They exist inside a container
called a project

All classes have at least one
method called main()

☕

▫ The main() method is the

starting point for JVM to
start execution of a Java
program

▫ Without the main()

method, JVM will not
execute the program

3 “Laws”

1. Every line ends with a ;

unless the next symbol is a
{

2. Every { has a }
3. Classes start with capital

letters, methods and
variables start with
lowercase letters

☕

Let’s Write our first Java
Program!!