Download - C5 applets v2
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Applets
Java y la WebApplets
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Temas
•Las diferencias entre Applets y aplicaciones.•Como crear un applets•Como colocar un applet en una pagina Web. •Como enviar información de un applet a la Web.
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Objetivos
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¿QUÉ ES UN APPLET?
Un applet es una mini-aplicación, escrita en Java, que se ejecuta en un browser (Netscape Navigator, Microsoft Internet Explorer, …) al cargar una página HTML que incluye información sobre el applet a ejecutar por medio de las tags <APPLET>... </APPLET>.
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Diferencia applets-Aplicación
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Características de los applets
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Para el programador
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Jerarquía de clases de applets
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Normas de seguridad
No pueden cargar programas almacenados en el sistema del usuario
El no puede ejecutar ningún programa en el sistema del lector.
No pueden comunicarse con un sitio de Internet que no sea aquel que sirvió la Pág. Web que lo incluye.
No pueden escribir archivos en el sistema de archivos del usuario.
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La clase Applet es la principal
La clase applet que se crea asume la forma siguiente:
public class yourApplet extends java.applet.Applet {
//código del applet aquí
}
La clase applet que se crea asume la forma siguiente:
public class yourApplet extends java.applet.Applet {
//código del applet aquí
}
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import java.awt. Graphics;import java.awt.Font;import java.awt.Color;
public class Palindrome extends Java.applet.Applet {
Font f = Font; (“TimesRoman”,Font.BOLD,36) ;
public void paint (Graphics screen) { screen.setFont(f); screen.setColor(Color.red); screen.drawString(“Go hang a salami,
I’m a lasagna hog.”, 5, 40);
}}
Ejemplo
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Un recorrido por los applets
ResumenResumen
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Applets and applications
An applet is a Java program that runs on a web page Applets can be run within any modern
browser To run modern Java applets, old browsers
need an up-to-date Java plugin appletviewer is a program that can run
An application is a Java program that runs all by itself
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Packages and classes
Java supplies a huge library of pre-written “code,” ready for you to use in your programs
Code is organized into classes Classes are grouped into packages One way to use this code is to import it You can import a single class, or all the
classes in a package
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The Applet class
To create an applet, you must import the Applet class This class is in the java.applet package
The Applet class contains code that works with a browser to create a display window
Capitalization matters! applet and Applet are different names
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Importing the Applet class
Here is the directive that you need: import java.applet.Applet;
import is a keyword java.applet is the name of the package A dot ( . ) separates the package from
the class Applet is the name of the class There is a semicolon ( ; ) at the end
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The java.awt package
“awt” stands for “Abstract Window Toolkit” The java.awt package includes classes for:
Drawing lines and shapes Drawing letters Setting colors Choosing fonts
If it’s drawn on the screen, then java.awt is probably involved!
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Ejemplo: Drawing rectangles
There are two ways to draw rectangles: g.drawRect( left , top , width , height );
g.fillRect(left , top , width , height );
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Applets Hola Mundo
// Applet HolaMundo de ejemplo // import java.awt.Graphics; import java.applet.Applet;
public class HolaMundo extends Applet { public void paint( Graphics g ) {
g.drawString( "Hola Mundo!",25,25 ) ; }
}