Java Fundamentals

Java Programming with Eclipse

Lecture 3

Eclipse IDE, Java syntax, types, and numerical operators

This work is licensed under CC BY-NC-SA 4.0

© Way-Up 2025

Summary of the last lecture

We have seen what is the UML notation, and applied it for class diagrams
It is now time to produce Java Code !

Summary of the last lecture

Who could define the 4 main concepts related to class relationship we've seen the last time?

Summary of the last lecture (2)

Our First Java Program : discovering IntelliJ IDEA and Java

For this lecture we will use IntelliJ IDEA
  • IntelliJ IDEA is one of the most popular Java IDEs
  • Provides intelligent code assistance and powerful refactoring
  • Community Edition is free and perfect for learning Java
  • Download from: jetbrains.com/idea

Using IntelliJ IDEA

IntelliJ IDEA Overview:
  • IntelliJ is organized around Projects
  • Project View: Shows your project structure and files
  • Editor: Where you write your code with intelligent completion
  • Tool Windows: Terminal, console, version control, debugging, etc.
  • Navigation: Double-tap Shift to search anything

Creating Your First Project in IntelliJ

Let's create a new Java project:
  • Open IntelliJ IDEA
  • Click New Project
  • Select Java and choose your JDK (Java 17+ recommended)
  • Name your project "JavaExercises"
  • Click Create
IntelliJ will automatically set up the project structure for you

Creating a Java Class

To create your first Java class:
  • Right-click on the src folder in Project view
  • Select New > Java Class
  • Enter the package name: fr.tbr.exercises
  • Enter the class name: JavaSyntaxDemo
  • Press Enter
IntelliJ creates the file with package declaration automatically

Java : From Object Concepts to Java

We will create our first Java Class

package fr.tbr.exercises;

public class JavaSyntaxDemo {
     private String demoVersion = "1.0_DEV";

     //Constructor
     public JavaSyntaxDemo() {

     }

     public String getDemoVersion(){
        return this.demoVersion;
     }

}

Code analysis

  • Comments 
    // This is a line comment

/* This is a block comment
it can contain several lines*/

/** This is a piece of javadoc, we will see this in detail after*/
  • Statements 
    ... ; //In Java, each statement must be finished by a semicolon
  • The package declaration 
    package fr.tbr.exercises;
// It provides a unique namespace to the class, and helps to locate the class

Code analysis (2)

  • Type concept: to tell that a field or a variable is of a certain type 
    Identity identity; // you should place the type name before the field
  • Constructors, are special methods called to create a new instance of a class 
    //Constructor declaration
Identity(){
}

void test(){
    Identity identity = new Identity(); //constructor call thanks to the "new" operator
}

Exercise

Remember the bank system? Create each class in eclipse
  • Each "text" typed field should be represented as a String
  • Each "numeric" typed field should be represented as a double
  • Do not represent links between classes, the goal is only to create each classes
  • Code help: String and double instantiations 
    
String message = "Hello World";
double amount = 10.2;

Exercise (2) : Class diagram

Different kinds of Type

In Java, you can meet two "kinds of type"

  • Primitive types, they are the builtin types of the language. They are not Objects
  • Object types, they all inherit from the Object class. Your own objects belong to that category

Different kinds of Type: Primitive types

Type Description Range
byte

a signed byte

-128 to 127
short

This is a two-bytes signed integer, it defaults to 0 if not initialized

-32,768 to 32,767
int

This is a signed integer, it defaults to 0 if not initialized

-2,147,483,648 to 2,147,483,647 (inclusive)

Different kinds of Type: Primitive types (2)

Type Description Range
long The long is a signed integer with a wider range. The declaration of a long is a bit different, you should do it as described below 
						
long primitiveLong = 1222222333335555l;
-9,223,372,036,854,775,808 to 9,223,372,036,854,775,807

Different kinds of Type: Primitive types (3)

Type Description Range
float

The float is a signed floating point number

1.40129846432481707e-45 to 3.40282346638528860e+38
double

The double is a type aiming at covering a very large range of values. However, its usage is discouraged since it is addressed on a 8 bytes format. If you use large tables of values, prefer float (if the range is ok for that)

4.94065645841246544e-324d to 1.79769313486231570e+308d
Other

Different kinds of Type: Primitive types (4)

Type Description Range
boolean

the boolean in Java can have two values true or false, which are reserved keywords of the language

true or false
char

2 bytes, unsigned, Unicode, char are used to represent characters, but are not directly compatible with integers or Strings

0 to 65,535

Numerical operators

There are several numerical operators :
  • addition 
    int i = 0;
i = i + 1;
  • subtraction 
    int i = 10;
i = i - 1;
  • multiplication 
    int i = 10 * 2;
  • division 
    int i = 10 / 2;

Numerical operators (2)

There are several numerical operators :
  • modulo 
    int i = 25 % 2; // i equals 1
  • increment 
    int i = 0;
i++; //i equals 1
  • decrement 
    int i = 10;
i--; //i equals 9

Exercise

  • Write a method computeInterest() in the class SavingAccount, that calculates the interest on one year, depending on the current amount at the computation time
  • Write a method withDraw() on the same class, that takes one parameter

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