Difference between revisions of "Java"

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(→‎Passing Object References)
Line 180: Line 180:
 
if(un.equals("Nathalie")){
 
if(un.equals("Nathalie")){
 
         ShowingData d = new ShowingData();
 
         ShowingData d = new ShowingData();
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}
 
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</syntaxhighlight>
 
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===Passing Object References===
 
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Ahora que nuestro programa está formado por diferentes archivos (diferentes class), veremos que en ocasiones, cuando creamos una «instance» de una class (Ej: «BasicShowData.java») dentro de, por ejemplo, «BasicLogin.java», podría ser necesario que «BasicShowData.java» colecte información de «BasicLogin.java». To do this, we will pass a reference across from the BasicLogin.java page to the «BasicShowData.java» page that will allow us to call back to the «BasicLogin.java» and access any variables or methods that it may have.
 
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Note que inside «», when we click the "Login" button, the actionListener method is then called and the BasicShowData class is just being created. Instead of just creating the «BasicShowData()» class, we are going to pass a reference to «this» current class that we are in (BasicLogin.java class). En otras palabras, cuando en «BasicLogin.java»  creamos la instance de «BasicShowData()» vamos a pasar una referencia de la clase donde estamos («BasicLogin.java») a través de '''«this»''':
 
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In BasicLogin.java:
 
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<syntaxhighlight lang="java">
 
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BasicShowData d = new BasicShowData(this);
 
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</syntaxhighlight>
 
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Now, in the «BasicShowData class», we must change the default constructor to catch «this» reference:
 
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<syntaxhighlight lang="java">
 
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public BasicShowData(BasicLogin ref) {
 
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</syntaxhighlight>
 
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De esta forma, la instancia de «BasicShowData class» puede acceder to all the variables and fields of the current class («BasicLogin.java»).
 
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{{#var:codespath}}PassingObjectReferences/src/BasicLogin.java
 
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<syntaxhighlight lang="java">
 
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import java.awt.GridLayout;
 
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import java.awt.event.ActionEvent;
 
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import java.awt.event.ActionListener;
 
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import javax.swing.JButton;
 
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import javax.swing.JFrame;
 
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import javax.swing.JLabel;
 
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import javax.swing.JTextField;
 
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public class BasicLogin extends JFrame implements ActionListener{
 
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JTextField username = null;
 
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JTextField password = null;
 
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public BasicLogin(){
 
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setSize(300,300);
 
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setVisible(true);
 
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this.setLayout(new GridLayout(3,2));
 
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JLabel un = new JLabel("Username");
 
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this.add(un);
 
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username = new JTextField(20);
 
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this.add(username);
 
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JLabel pw = new JLabel("Password");
 
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this.add(pw);
 
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password = new JTextField(20);
 
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this.add(password);
 
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JButton button = new JButton("Login!");
 
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button.addActionListener(this);
 
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this.add(button);
 
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validate();
 
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repaint();
 
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}
 
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public static void main(String[] args){
 
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new BasicLogin();
 
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}
 
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@Override
 
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public void actionPerformed(ActionEvent arg0){
 
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// TODO Auto-generated method stub
 
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BasicShowData d = new BasicShowData(this);
 
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}
 
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}
 
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</syntaxhighlight>
 
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{{#var:codespath}}PassingObjectReferences/src/BasicShowData.java
 
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<syntaxhighlight lang="java">
 
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import javax.swing.JFrame;
 
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import javax.swing.JLabel;
 
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public class BasicShowData extends JFrame {
 
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public BasicShowData(BasicLogin ref) {
 
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String username = ref.username.getText();
 
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setSize(300,300);
 
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setVisible(true);
 
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JLabel tx = new JLabel("They logged in as: " + username);
 
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this.add(tx);
 
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}
 
 
}
 
}
 
</syntaxhighlight>
 
</syntaxhighlight>

Revision as of 12:02, 10 June 2019

Path de los códigos: 

Variable definida con:
{{#vardefine:codespath|/home/adelo/1-disco_local/.archivos_programas/eclipse-workspace/}}

Para usar la variable:
{{#var:codespath}}

Instalación de Java

Installing the Default OpenJDK

http://ubuntuhandbook.org/index.php/2018/11/how-to-install-oracle-java-11-in-ubuntu-18-04-18-10/ 

sudo apt update

sudo apt install default-jdk

Oracle Java Development Kit JDK

https://en.wikipedia.org/wiki/Java_Development_Kit

https://www.oracle.com/technetwork/java/javase/overview/index.html

Es apropiado instalar Oracle JDK. Para GUI Programming, por ejemplo, se necesitan librerías que se encuentran en Oracle JDK.

Hay diferentes Edition:

  • Java Platform, Standard Edition (Java SE) (ésta es la que generalmente necesitamos)
  • Java Platform, Enterprise Edition (Java EE)
  • Java Platform, Micro Edition (Java ME)
  • ...

Installing Oracle JDK on Ubuntu

Installing Oracle JDK (Java EE) on Ubuntu 18.04: http://ubuntuhandbook.org/index.php/2018/11/how-to-install-oracle-java-11-in-ubuntu-18-04-18-10/

En una ocasion, al instalar java-10-oracle la instalación de NetBeans no funcionó correctamente. Esto creo que se debía a que Java-10-oracle era muy reciente para la fecha. Fue por tanto necesario instalar java-8-oracle y configurar la ruta del JDK editando el archivo /usr/local/netbeans-8.2/etc/netbeans.conf

Installing Oracle JDK on Windows

Installing Oracle JDK (Java EE) on Windows:

  • Descargar Java SE de la página oficial de Oracle:
https://www.oracle.com/technetwork/java/index.html
https://www.oracle.com/technetwork/java/javase/downloads/index.html
  • Instalación común sin ninguna remarca.
  • Los archivos se guardan generalmente by default en: C:\Program Files\Java
    • Cuando instalé NetBeans, éste detectó automáticamente la ruta del JDK - JDK for the NetBeans IDE:
C:\Program Files\Java\jdk1.8.0_181

Check your installed java version

java  -version
javac -version


The fallowing command should tell you what is currently providing the Java virtual machine (java) and the Java compiler (javac): https://askubuntu.com/questions/150057/how-can-i-tell-what-version-of-java-i-have-installed 

file /etc/alternatives/java /etc/alternatives/javac

Eclipse

Installing Eclipse

Para estar seguro de que estamos instalando la última versión, es apropiado descargar el paquete desde la página oficial, y no instalar la versión que se encuentra en los repositorios de Ubuntu a través de apt-get (pues estar versiones generalmente están desactualizadas).

Página oficial de Eclipse: http://www.eclipse.org/downloads/

En la siguiente página se explica como instalar eclipse en Ubuntu 16.04: http://ubuntuhandbook.org/index.php/2016/01/how-to-install-the-latest-eclipse-in-ubuntu-16-04-15-10/

Para instalarlo hay que simplemente ejecutar el instalador y seguir las instrucciones (como si se tratara de una instalación en Windows).

Luego, para agregar el ejecutable a la lista de comandos, he agregado la siguiente línea en el .bashrc: 

PATH=$PATH:/home/adelo/1-system/.1-conf-system/1-archivos_programas-ubuntu/eclipse/java-photon/eclipse:

Combinaciones de teclas

  • Para que coloque los import (luego de haber ingresado un comando que necesite una librería en particular): Ctrl Shif o
  • Run: Ctrl 11
  • Comentar: Ctrl 7
  • Rastrea la variable seleccionada: CTRL k

NetBeans

https://netbeans.org/

https://en.wikipedia.org/wiki/NetBeans

Installing NetBeans on Ubuntu 18.04

https://www.itzgeek.com/how-tos/linux/ubuntu-how-tos/how-to-install-netbeans-ide-on-ubuntu-18-04-ubuntu-17-10.html

Se puede descargar NetBeans manualmente de la página oficial: https://netbeans.org/downloads/

o a través de wget: 

wget http://download.netbeans.org/netbeans/8.2/final/bundles/netbeans-8.2-linux.sh

Luego: 

sudo bash netbeans-8.2-linux.sh

Durante la instalación es importante seleccionar el directorio en donde se encuentra Java, en mi caso: 

/usr/lib/jvm/java-8-oracle
/usr/lib/jvm/java-10-oracle

Con java-10-oracle la instalación no funcionó correctamente. Fue por tanto necesario instalar java-8-oracle y configurar la ruta del JDK editando el archivo /usr/local/netbeans-8.2/etc/netbeans.conf

Uninstall NetBeans

https://askubuntu.com/questions/76908/how-to-uninstall-netbeans

Sólo hay que ejecutar el script uninstall.sh in /usr/local/netbeans-x.x 

bash uninstall.sh

Installing NetBeans on Windows 10

  • Descargar NetBeans de la página oficial: https://netbeans.org/downloads/
  • Cuando instalé NetBeans, éste detectó automáticamente la ruta del JDK - JDK for the NetBeans IDE:
C:\Program Files\Java\jdk1.8.0_181
  • Debido a que instalé la versión que tiene todos los componentes, se instaló también el GlassFish Server Open Source Edition. No sé para que es sirve y si sea apropiado instalarlo.

The Darcula plugin

In NetBeans IDE 8.2 you can now go to:

  • Tools > Plugins > Available Plugins > and install the Darcula LAF for NetBeans plugin directly from there.
  • En las versiones 9 y 10 el Plugin no se encuentra disponible por defecto. Es entonces necesario adicionarlo a la lista de "Available Plugins" de la siguiente forma:
https://stackoverflow.com/questions/52688439/changing-theme-in-apache-netbeans-9-0

Jar File

A Jar File (acronym for Java Archive) is format used for archiving java files (merging several java files into one)

The Jar File, provides a method to package our software to give it to the users.

The Jar File can be Runnable. That is, when we double click it, our program will run.


A typical extension to files that we have always seen when working in a Windows environment is the .exe file extension. These files are a single binary executable file that when double clicked will open the program for the user.

In the Java world however things are a little different. There is no native .exe file in Java and we must use the .jar file extension instead. A jar file works exactly the same as a .exe file and when double clicked will run the program.

Jar files come in two different varieties:

  • Simple archive folder
  • Runnable archive folder

A jar file is an acronym for Java Archive. Simple archive folder is a filetype similar to that of the .zip extension. If we want, we can open up a jar file using a program such as WinZip or WinRar and check the contents inside of the jar.

The second variant of this is the ​runnable archive folder​. This type of file is exactly the same as the archive folder, just with one additional file. This extra file is used to define what happens when the user double clicks on the icon. In our case, we will point to the main method in our class file that we want to run. This will kick start the program to run when it is double clicked.

Creating a Jar

Open up your Eclipse and navigate to the project you are currently working on. Note this will only work correctly with an application that has a GUI for the user to see. In this case the project we are looking at is called Sample Program 1.

  • Right click on the project name, and a menu will open.
  • In the menu that opens, click on the Export button.
  • In the window that opens you will see that two different types of JAR file are available:
    • If you wanted to simply package your project to give to someone, you could use the JAR file.
    • In our case, we are interested in the Runnable JAR file, so we will click on this option and then click Next.
  • You will then be passed to a second window where you will be able to specify the details for the runnable Jar file you are about to create:
    • The first of these is the launch configuration. This is the most important step to ensure that your Jar file will open the project when it is double clicked.
      • Select the name of the class you want to run, inside of the project that you have been working on. In this case, you can see that the Main class is selected which is inside of the project titled SampleProgram1 that we are working in.
    • The second step is then to select a location where we would like to export the Jar file to.
    • After you have finished, click Finish at the bottom of the page.
  • A small warning message may pop up, but this is ok. Click Ok to ignore this message.

Exploring the Jar File

Now that we have created the Jar file. If we double click on the file our program will run. However if we want, we can take a look inside of the Jar file. This is easily done by right clicking on the Jar file that we have created and clicking “Open with WinRAR” or whichever program you currently have installed on your system for viewing Zip files.

After WinRAR has opened you will be able to see the contents of the Jar file. In this case you can see the class file from the project that we have been developing. In addition to this, you will see an additional folder titled META-INF. This is the folder where all of the configuration for the Jar file are held. We will go into this folder and take a look around.

Inside of this folder, you will see a file titled MANIFEST.MF. This is the main configuration file for the Jar file we have created. If we open up this file, we can see the details of what is called when we double click on the Jar file to view it.

There is very little content that is needed to make the Jar file run. Inside of this file, you can see that the Main-Class attribute is set to the name of the class file that we want to run when the Jar is double clicked. In the case of this project, the class file that we want to run is called Main.class, so the title Main is used as the value for this attribute. If your class was called MyProgram.class, this would be set to MyProgram.

Expanding our program across multiple files (Classes)

Although we have developing all of our code inside a single java file, it is common practice to break the application down into smaller individual classes.

We will only ever have one main method. In this case, our Login.java is the file that will have the main method. No other class should have a main method!

Para integrar distintas «class» lo único que tenemos que hacer es tener los archivos en el mismo directorio y crear una instancia de la «class». En el siguiente ejemplo hemos creado una instancia de la «class» ShosingData en Login.java. En este caso, si se cumple el IF, se ejecutará «ShowingData.java». 

Fracmento de /home/adelo/1-disco_local/.archivos_programas/eclipse-workspace/DBtest/src/Login.java

if(un.equals("Nathalie")){
        ShowingData d = new ShowingData();
}
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