Download JAVA PROGRAMMING - Lesson 2

JAVA PROGRAMMING
LESSON 2
CREATING A JAVA APPLICATION
Compiled By: Edwin O. Okech [Tutor, Amoud University]
Outline
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.
i.
Compiled By: Edwin O. Okech [Tutor, Amoud University]
Steps to Creating a Java Application
Create/ Modify the
Source Code using Text
Editor
If Error
Compile Source Code
using Java Compiler
Saves on Disk
Produces
If Run Time Error or Incorrect results
Run Byte Code using Java
Virtual Machine
Compiled By: Edwin O. Okech [Tutor, Amoud University]
Results
Source Code
(.java)
Byte Code
(.class)
Program
Execution
Create a Source File
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.
1.
Compiled By: Edwin O. Okech [Tutor, Amoud University]
Demonstrate how to open a Java IDE
e.g. Netbeans
 Start - Programs – Netbeans
 Example 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");
}
}
Compiled By: Edwin O. Okech [Tutor, Amoud University]
Analyzing the Example HelloApp.java
// This is my first Java program.
public class HelloApp
{
This is a Java comment, it is
ignored by the Java compiler
This is the class header for the
HelloApp class
This are is the body of the class HelloApp. All of
the data and methods for this class will be
between the curly braces
}
Compiled By: Edwin O. Okech [Tutor, Amoud University]
Analyzing the Example HelloApp.java
// This is my first Java program.
public class HelloApp
{
This is Java main method.
Every application must have a
main method.
public static void main (String args[])
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
}
}
Compiled By: Edwin O. Okech [Tutor, Amoud University]
Analyzing the Example HelloApp.java
// 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”);
}
}
This is the Java statement that is executed
when the program runs
Compiled By: Edwin O. Okech [Tutor, Amoud University]
Structure of Java programme
 Comments
 Keywords
 Modifiers
 Statements
 Blocks
 Classes
 Methods
 The main method
 Package
Compiled By: Edwin O. Okech [Tutor, Amoud University]
Comments
 Help the programmers to communicate and understand the
program.
 Not a programming statement, thus ignored by the compiler.
 Three Types of Comments:
1.
2.
3.
Multiline comments
Single line comments
Javadoc comments
Compiled By: Edwin O. Okech [Tutor, Amoud University]
Multi line Comments
/*
This is a comment with
four lines of
text.
Make sure you have the pair.
*/
Compiled By: Edwin O. Okech [Tutor, Amoud University]
Single line comments
// This is a single line comment
// Each line must have the double back slash
Compiled By: Edwin O. Okech [Tutor, Amoud University]
Javadoc comments
/**
* This program converts the temperature value in
* Celsius into Fahrenheit.
*/
Compiled By: Edwin O. Okech [Tutor, Amoud University]
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.
Compiled By: Edwin O. Okech [Tutor, Amoud University]
Java keywords
abstract
boolean
extends
new
throw
char
goto
return
const
implements
short
while
else
break
final
package
throws
class
if
try
continue
import
static
double
long
byte
finally
private
transient
float
protected
void
default
instanceof
strictfp
interface
Compiled By: Edwin O. Okech [Tutor, Amoud University]
synchronized
case
native
this
catch
for
public
volatile
do
int
super
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
Compiled By: Edwin O. Okech [Tutor, Amoud University]
Modifiers: examples
public class ClassA
{
public static void main (String[] args)
{
System.out.println ("Try your best");
}
}
Compiled By: Edwin O. Okech [Tutor, Amoud University]
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 (;).
Compiled By: Edwin O. Okech [Tutor, Amoud University]
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.
Compiled By: Edwin O. Okech [Tutor, Amoud University]
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.
Compiled By: Edwin O. Okech [Tutor, Amoud University]
Example of a class
public class ClassA
{
public static void main (String[] args)
{
System.out.println ("Try your best");
}
}
Compiled By: Edwin O. Okech [Tutor, Amoud University]
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).
Compiled By: Edwin O. Okech [Tutor, Amoud University]
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;
}
}
Compiled By: Edwin O. Okech [Tutor, Amoud University]
main Method
 Every Java application must have main a method that is
declared in the following way:
public class ClassName
{
public static void main(String[] args)
{
// Statements;
}
This method is public i.e. visible from
}
anywhere that can see this class.
Compiled By: Edwin O. Okech [Tutor, Amoud University]
main Method
 Every Java application must have main a method that is
declared in the following way:
public class ClassName
{
public static void main(String[] args)
{
// Statements;
The main method is always static,
}
meaning that this method can be run
}
without creating an instance of the class
Compiled By: Edwin O. Okech [Tutor, Amoud University]
main Method
 Every Java application must have main a method that is
declared in the following way:
public class ClassName
{
public static void main(String[] args)
{
// 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
Compiled By: Edwin O. Okech [Tutor, Amoud University]
main Method
 Every Java application must have main a method that is
declared in the following way:
public class ClassName
{
public static void main(String[] args)
{
// 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.
Compiled By: Edwin O. Okech [Tutor, Amoud University]
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 classes
 java.awt — windowing and graphics toolkit
 javax.swing — GUI development package
Compiled By: Edwin O. Okech [Tutor, Amoud University]
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.
Compiled By: Edwin O. Okech [Tutor, Amoud University]
import statement
 Full library class names include the package name. For
example:
java.awt.Color
javax.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");
Compiled By: Edwin O. Okech [Tutor, Amoud University]
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.
Compiled By: Edwin O. Okech [Tutor, Amoud University]
THE END
END JAVA PROGRAMMING - LESSON 2
(CREATING A JAVA APPLICATION)
Compiled By: Edwin O. Okech [Tutor, Amoud University]