LESSON 2 CREATING A JAVA APPLICATION JAVA PROGRAMMING Compiled By: Edwin O. Okech [Tutor, Amoud...

LESSON 2CREATING A JAVA APPLICATION

JAVA PROGRAMMING

Compiled By: Edwin O. Okech [Tutor, Amoud University]

Outlinei. Create Java source file in DOS

environment.ii. Compile the Java source file at the DOS

prompt.iii. Run the Java byte code file at the DOS

prompt.iv. Analyze the Java program.v. Determine the structure of the Java

program.


Steps to Creating a Java Application


Create/ Modify the Source Code using Text Editor

Compile Source Code using Java

Compiler

Run Byte Code using Java Virtual

Machine

Source Code (.java)

Byte Code (.class)

Program Execution

Saves on Disk

Is Read By

Is Interpreted

By

Produces

Results

If Error

If Run Time Error or Incorrect results

Create a Source File


1. Create a new directory in drive C to place all your Java source files.

2. Open a text editor i.e. Notepad.3. Type the Java code.4. Save the code to a file. The name of the file must be the same as

the class name and with the extension name .java.

Demonstrate how to open a Java IDE e.g. Netbeans


Start - Programs – NetbeansExample Code

// This is my first Java program.public class HelloApp{

public static void main(String [] args){

System.out.println("Hello there");System.out.println("Welcome to Java");

}}

Analyzing the Example HelloApp.java



}

This is a Java comment, it is ignored by the Java compiler

This is the class header for the

HelloApp classThis are is the body of the class

HelloApp. All of the data and methods for this class will be

between the curly braces




public static void main (String args[]){

}}

This is Java main method. Every

application must have a main method.

This area is the body of the main method. All of the actions to be completed

during the main method will be placed between these

curly braces




public static void main (String args[]){

System.out.println(“Hello there”);System.out.println(“Welcome to

Java”);}

}This is the Java statement that is executed when the

program runs

Structure of Java programme


CommentsKeywordsModifiersStatementsBlocksClassesMethodsThe main methodPackage

Comments


Help the programmers to communicate and understand the program.

Not a programming statement, thus ignored by the compiler.

Three Types of Comments:1. Multiline comments2. Single line comments3. Javadoc comments

Multi line Comments


/*This is a comment withfour lines oftext.Make sure you have the pair.*/

Single line comments


// This is a single line comment// Each line must have the double back

slash

Javadoc comments


/*** This program converts the temperature

value in* Celsius into Fahrenheit.*/

Java keywords


Words that have a specific meaning to the Java compiler.

Key words are lower case (Java is a case sensitive language).

Key words cannot be used as a programmer‐defined identifier.

Java keywords


abstract else long synchronized boolean break byte case extends final finally nativenew package private this throw throws transient catch char class float for goto if protected public return try void volatile const continue default do implements import instanceof int short static strictfp super while double interface switch

Modifiers


Specify the properties of the data, methods, and classes and how they can be used.

Example of modifiers:- public: data, method or class can be

accessed by other classes.- private: data, method or class cannot be

accessed by other classes.- protected- final- static- abstract

Modifiers: examples


public class ClassA{

public static void main (String[] args) {

System.out.println ("Try your best");}

}

Statements


Represents an action or a sequence of actions.

• Example of statement:System.out.println("Welcome to Java!")is a statement to display the greeting:"Welcome to Java!"• Every statement in Java ends with a

semicolon (;).

Statement blocks


Groups the components of the program using the braces { and } in the program.

Every class has a class block that groups the data and the methods of the class.

Every method has a method block that groups the data and the methods of the class.

Block may be nested, meaning that one block can be placed within another.

Classes


A class is the blue of an object.A class is the template of an object.Class is the essential Java construct.Classes are central to Java.Programming in Java consists of defining a

number of classes:– Every program is a class (a program is

defined by using one or more classes).– All programmer‐defined types are classes.

Example of a class


public class ClassA {

public static void main (String[] args) {

System.out.println ("Try your best");}

}

Methods


A collection of statements that performs a sequence of operations.

Contained in a class.If a method is intended to be used to

communicate with or pass information to an object, it should be declared public.

Example: Method println()is an instance method that belongs to an object instance and is applied to an object (System.out).

main Method


Every Java application must have a main method that is declared in the following way:

public class ClassName{

public static void main(String[] args) {

// Statements;}

}

main Method


Every Java application must have main a method that is declared in the following way:



// Statements;}

}

This method is public i.e. visible from anywhere that

can see this class.

main Method





// Statements;}

}

The main method is always static, meaning that this

method can be run without creating an instance of the

class

main Method





// Statements;}

}

The void keyword indicates that the data returned from this method is nothing or no value i.e. it does not return a

value

main Method





// Statements;}

}

This is the parameter of the main method. It takes arguments of an array of Strings.

The data type String starts with an uppercase S. the square brackets indicate

an array.

Libraries


Java programs are usually not written from scratch.

There are hundreds of library classes for all occasions.

Library classes are organized into packages. For example:

java.util — miscellaneous utility classesjava.awt — windowing and graphics toolkitjavax.swing — GUI development package

Packages


Java is a package‐centric language; for good organization and name scoping, put all classes into packages.

A class with default access can be seen only by classes within the same package.

If class A and class B are in different packages, and class A has default access, class B won't be able to create an instance of class A, or even declare a variable or return type of class A.

import statement


Full library class names include the package name. For example:java.awt.Colorjavax.swing.JButton

import statements at the top of the source file let you refer to library classes by their short names:import javax.swing.JButton; Fully-qualified

...JButton go = new JButton("Go");

Import statements


You can import names for all the classes in a package by using a wildcard .*:import java.awt.*;import java.awt.event.*;import javax.swing.*;

The above Imports all classes from awt, awt.event and swing packages.

java.lang is imported automatically into all classes; defines System, Math, Object, String, and other commonly used classes.

THE END


END JAVA PROGRAMMING - LESSON 2(CREATING A JAVA APPLICATION)

LESSON 2 CREATING A JAVA APPLICATION JAVA PROGRAMMING Compiled By: Edwin O. Okech [Tutor, Amoud...

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