Java Programming, 3e Concepts and Techniques Chapter 2 - Part 2 Creating a Java Application and Applet.

Java Programming, 3eConcepts and Techniques

Chapter 2 - Part 2Creating a Java

Application and Applet

2Chapter 2: Creating a Java Application and Applet

Chapter Objectives

• Code output• Use the println() method• Compile a Java program• Understand the common types of errors• Run a Java Program• Edit Java source code to insert escape

characters and a system date• Print source code

3Chapter 2: Creating a Java Application and Applet

Chapter Objectives

• Differentiate between an application and an applet

• Create an applet from Java source code

• Write code to display a graphic, text, color, and the date in an applet

• Create an HTML host document

• Run a Java applet

4Chapter 2: Creating a Java Application and Applet

Coding Output

• Call the System.out.println() method in the SDK to display output to the monitor– System is the class– out is the object representing the default display– println() is the method

5Chapter 2: Creating a Java Application and Applet

Coding Output

• When calling a method, arguments are placed in parentheses– String literals are placed in quotation marks– Numeric literals and variables do not need quotation

marks

• Period delimiters separate the class, object, and method

• Semicolons must be placed after every statement except headers and braces

• Braces { } enclose the body of a method

6Chapter 2: Creating a Java Application and Applet

Testing the Solution

• Compile the source code– Clean and Build

• If the compiler detects errors, fix the errors and compile again

• If the compilation was successful, run the program

7Chapter 2: Creating a Java Application and Applet

Debugging the Solution

• System Errors– System command is not set properly– Software is installed incorrectly– Location of stored files is not accessible

• Syntax Errors– One or more violations of the syntax rules of Java

• Semantic Errors– The code meaning is unrecognizable to the compiler

• Logic and Run-Time Errors– Unexpected conditions during execution of a program

8Chapter 2: Creating a Java Application and Applet

Debugging the Solution

9Chapter 2: Creating a Java Application and Applet

Running the Application

• After compilation is successful, run the program to test for logic and run-time errors

• Use the Run command

• Use the java command from the command prompt – Syntax: java classname (no extension)

10Chapter 2: Creating a Java Application and Applet

Editing the Source Code

11Chapter 2: Creating a Java Application and Applet

Java Code Packages

• The Java Software Development Toolkit (SDK) provides libraries of code which can be used in programs.

• System.out.println() is a method provided in the SDK.

12Chapter 2: Creating a Java Application and Applet

Import Packages

• Use the import statement to access classes in the SDK– The java.lang package is automatically

imported– Place the import statement before the class

header– Use an asterisk (*) after the package name

and period delimiter to import all necessary classes in the package

13Chapter 2: Creating a Java Application and Applet

14Chapter 2: Creating a Java Application and Applet

Call a System Date Constructor

• Use the Date class in the java.util package to access the system date

• Store the Date in an object variable• Declare the object variable by calling the Date

constructor– The constructor is a method denoted by the new

keyword followed by the object type and parentheses– Declaration syntax:

objectType variableName = new objectType();

15Chapter 2: Creating a Java Application and Applet

Format Output Using Escape Characters• Use escape characters inside String arguments

to move the output of data

16Chapter 2: Creating a Java Application and Applet

Editing the Source Code - cont.

• Recompile and run the application– The bytecode should be updated after any

changes to the source code

17Chapter 2: Creating a Java Application and Applet

Moving to the Web

• Characteristics of an applet – Applets run within a browser/viewer and are usually

delivered to the client machine via the Web– Applets cannot use system resources or files on the

client machine

• Convert the application into an applet– Import two packages– Change the class name and extend the Applet class– Include a paint method to draw text and display color

and a graphic

18Chapter 2: Creating a Java Application and Applet

Import Applet Packages

• Applet package (java.applet.*)– Allows applets to inherit attributes and

methods

• AWT package (java.awt.*)– Provides access to color, draw methods, and

GUI elements

19Chapter 2: Creating a Java Application and Applet

20Chapter 2: Creating a Java Application and Applet

Creating a Java Applet Class

• Right click on the Welcome package and select New– If “Applet” is not listed click on “Other” and

choose “Applet” and click Next

• Set the Class Name to “WelcomeApplet” and the package to “welcome”

• Click Finish

21Chapter 2: Creating a Java Application and Applet

Adding the Java SDK packages

• Add:import java.util.Date;

import java.awt.*;

22Chapter 2: Creating a Java Application and Applet

The paint() Method

• Accepts a Graphics object as a parameter

• The Graphics object is commonly referred to by the variable name g– The variable g is a reference variable, or a

specific instance of an object

• The return type is void

23Chapter 2: Creating a Java Application and Applet

The drawString() Method

• Displays text in the applet window

• Accepts three arguments– The String data

• If the data is not a String object, convert it to a String object using the toString() method

– The horizontal and vertical coordinates of the String

• The coordinates are measured in pixels

• Called by the Graphics object, g

24Chapter 2: Creating a Java Application and Applet

Draw an Image

• Declare an Image object• Use the getImage() method to load the image

– The getImage() method calls the getDocumentBase() method to pull the image from the current folder

• Use the drawImage() method to set the coordinates of the image

25Chapter 2: Creating a Java Application and Applet

Set the Background Color

• Use the setBackground() method to change the background color of the applet window– The setBackground() method does not need to be

called from a reference variable

26Chapter 2: Creating a Java Application and Applet

Creating an HTML Host Document• A host program, such as a Web page executes

the applet

• If you run the file, NetBeans will build a HTML file for you in the “build” folder.– Copy the image.gif file into the folder and open the

HMTL

27Chapter 2: Creating a Java Application and Applet

Final Result…

28Chapter 2: Creating a Java Application and Applet

Rest of Today

• Create the Java Applet for the Welcome Program– Add your name to Applet– Pick a different color

• Show me the result when your done