Java Tutorial
Prepared for PEO Mississauga Chapter
Online High School Coding Challenge 2023
A Quick Introduction
My name is Les Carbonaro.
I am a software developer, mainly full-stack web application development.
I also host a beginner-friendly meet-up group called Mississauga Coding.
Pre-requisites
Either download and install the JDK and a code editor or IDE.
Or, use one of the many online Java compilers available.
Will be using OnlineGDB for all the examples in this tutorial.
- OnlineGDB
- Codiva
- OneCompiler
- CodingRooms
- ReplIt
- a number of others ...
Why Learn/Use Java?
- Versatile & portable across platforms & applications
- Used across several industries
- In high demand
- Excellent community support
- Clearly structured applications
Who invented Java?
James Gosling started developing Java in 1991 while working for Sun Microsystems.
Basic File Structure
Basic Source File Structure
Basic Source File Structure
// 1. everything needs to be inside a class
public class Main {
}
Basic Source File Structure
// 1. everything needs to be inside a class
public class Main {
// 2. every class needs at least one method
public static void main(String[] args) {
}
}
Basic Source File Structure
// 1. everything needs to be inside a class
public class Main {
// 2. every class needs at least one method
public static void main(String[] args) {
}
}
Basic Source File Structure
// 1. everything needs to be inside a class
public class Main {
// 2. every class needs at least one method
public static void main(String[] args) {
/*
a method contains programming logic
*/
} // end of method block
// other methods, if any, go here
} // end of class block
Outputs
// 1. everything needs to be inside a class
public class Main {
// 2. every class needs at least one method
public static void main(String[] args) {
/*
a method contains programming logic
*/
// some output message
System.out.println("Hello World");
}
}
Some Variable Types
(The most commonly used)
- int
- float
- double
- boolean
- char
- String
Variable Type Conversion
(Also known as Casting)
Think of variables as boxes in memory.
The size of the box depends on the variable type.
Automatic or implicit - when going to a bigger box
Manual or explicit - when going to a smaller box
Inputs
Programs typically need input(s).
One way is to prompt user to enter a value.
Java has built-in methods for this purpose.
Inputs
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
Scanner scan = new Scanner(System.in);
System.out.println("What is your name:");
String name = scan.nextLine();
System.out.println("Hello " + name);
}
}
Inputs cont.
// 1. import the required Java libraries
import java.io.InputStreamReader;
import java.io.BufferedReader;
import java.util.StringTokenizer;
import java.io.IOException;
public class Main {
public static void main(String[] args) {
System.out.println("Enter item qty price");
// 2. set up readers & tokeniser
InputStreamReader isr = new InputStreamReader( System.in );
BufferedReader br = new BufferedReader(isr);
StringTokenizer st = null;
// 3. read input line
// note that must catch exception
try {
st = new StringTokenizer(br.readLine());
} catch(IOException e) {
e.printStackTrace();
}
// 4. tokenise (chop up) the input into respective variables
// note parse methods for int, float
String item = st.nextToken();
int qty = Integer.parseInt( st.nextToken() );
float price = Float.parseFloat( st.nextToken() );
// use input variables as needed
System.out.println("input item is: " + item);
System.out.println("input qty is: " + qty);
System.out.println("input price is: " + price);
}
}
Some Useful String methods
What was Java called originally?
Java was originally called Oak, after a tall oak tree outside James Gosling's office window.
Operators
Arithmetic
Assignment
Some Useful Math methods
More Operators
Comparison
Logical
Conditional Statements
(a.k.a. IF statements)
If something is true then do this, otherwise do that.
if( condition ) { // if block
// do something
} else { // else block
// do some other thing
}
Arrays
A list or group of values; a collection
Multiple values in one variable
- fixed number of values
- same data type
- access by zero-based index
- can be multi-dimensional
For-Loop Statements
For
for( initialise; check; increment ) {
// Code to be executed on each iteration
}
For-Each
for(dataType variableName : arrayName) {
// Code to be executed on each element
}
While-Loop Statements
While
while(condition) {
// Code to be executed as long as the condition is true
}
Do-While
do {
// Code to be executed at least once
} while(condition);
Switch-Case Statement
switch(variable) {
case value1:
// code to be executed if expression matches value1
break;
case value2:
// code to be executed if expression matches value2
break;
// additional case statements if needed
default:
// code to be executed if none of the above cases match
}
Methods
(a.k.a. functions in other languages)
Reusable snippets of code
- DRY principle
- divide & conquer
- better code organisation, reusability, and modularity
Methods cont.
accessModifier returnType methodName(parameterList) {
// code to be executed
// optionally, a return statement to return a value
}
Define method once
Call it as many times as needed
What year was Java launched?
Java 1.0 came out in 1996.
Object-Oriented Programming
Custom-made classes
- variables and related methods
public class ClassName {
// Class attributes (a.k.a. variables, properties, fields)
// Class methods
}
OOP cont.
Classes vs Objects
- class is the blueprint
- object is a variable made from that blueprint
An object is an instance of a class
Where To Find More
Any questions?