CIS3931 - Intro to JAVA

Lecture Notes Set 1319-July-05

GUI Programming –TextField Action Listeners, JEditorPane action listeners, HTML

in a JEditorPane, JAR Files

Reminder…

• As stated in the syllabus, you must pass the final in order to pass the class.

• Anyone who receives below a 70 on the final will fail the class regardless of how high your other grades are.

• The majority of the final will be repeated questions from Midterm 1 and 2. There will only be a few new questions from the material we have covered since Midterm 2.

• A review for the final will take place on the 2nd of August.

Reminder…

• Additionally, some review material will be posted online. Specifically, I will list the things that you will need to know for the final.

• As with Midterm 1 and 2, there will be extra credit available. It will be very similar to the extra credit that was given on Midterm 2.

Reminder…

• If there are any problems with your grades, you need to let me know immediately. Grades will be submitted the Monday after the last week of class. No grade changes will be permitted after this date.

Reminder …

• If you would like to see a copy of your Midterm 1 or Midterm 2, please stop by my office. It is recommended that you call before you come over to be sure that I am in the office (644-8562)– This is a community office number … please

ask for Bobby when you call …

Adding actions to a TextField

• When creating the webbrowser, you need to tell your program to “load” whatever is in the textfield for your URL.

• Assign listener to the text field so when the user hits “return”, the textfield performs an action.

Adding actions to a TextField//First, create the textFieldJTextfield sampleTextField = new JTextField(“Enter text

here”);

//Assign an action listener to the textfieldsampleTextField.addActionListener(new

ActionListener() { public void actionPerformed(ActionEvent event) { //PUT YOUR ACTION CODE HERE }}});

Adding actions to a TextField

• Example : Creating a TextField that will allow the user to change the text displayed in an JEditorPane

• See textaction.java

Turning a JEditorPane into an HTML viewer

• JEditorPane has a method called setPage (String s)

• setPage will load an HTML page into the editor pane

• Pass the string containing the URL into the setPage method

• Since you are dealing with I/O (loading a page from the internet uses an input stream), you need to handle I/O errors by using a try/catch block.

Example method for loading a URL

public void showURL(String urlString) { try { //Try to load the webpage samplePane.setPage(urlString); } catch (Exception exception) { //If there is an error, inform the user //by placing text on the EditorPane samplePane.setText("Couldn't open the url : " + urlString + " Reason for error : " + exception); }}

Using the showURL method

• showURL takes in a String as its parameter. It doesn’t return anything.

• showURL is a very primitive way to load a URL … you will need to expand upon it slightly when using it for your web browser.

• See htmleditorpane.java for example

• Note : This example only loads http://www.google.com into the JEditorPane. Notice that the links on google’s page won’t work. Making links work will come later in the slides.

Making the links work…

• As with everything in JAVA, there needs to be an action listener associated with the links on webpages in order to get them to work.

• Luckily we don’t have to write an action listener for every link on every page (which would be impossible…)

• Simply assign a “catch all” action listener to the JEditorPane to load pages when a the use clicks on the link…

• Special actionListener called “HyperlinkListener” exists to handle such a request …

Making the links work … the HyperlinkListener

//Assuming the JEditorPane is called samplePanesamplePane.addHyperlinkListener(new HyperlinkListener() { public void hyperlinkUpdate(HyperlinkEvent event) { //Check to see if the user clicked on a link if (event.getEventType() == HyperlinkEvent.EventType.ACTIVATED) { //Call our showURL function //event.getURL() gets the URL from the link showURL("" + event.getURL()); } } });

The back and forward buttons

• Count as 10 (of 100) points for Program 6.

• The back and forward buttons are not easy to make …

• If you have trouble with the buttons, just do one of the extra credit things instead

Creating the back and forward buttons

• Can be done with an array• Store each page you visit in the array while

keeping track of your “index” position in the array.

• Hitting the forward button should load the next URL in the array (and increment your current index position by 1)

• Hitting back button should should load the previous URL in the array (and decrement your current index position by 1)

Creating the back and forward buttons

• Check for duplicate URLs being added in a row (example : hitting the “home” button 3 times in a row should not add the home URL three times in a row to the array)

• Make sure you are checking and adding to the array EVERY TIME you click on a link or load a URL from the textfield

JAR Files

• JAVA Archive files – similar to the UNIX TAR file (… actually, the exact same format).

• Used to contain multiple JAVA source and class files in one file

• Can be used to create a packaged “executable” version of your program– Note : The computer executing the JAR file will still

need to have the JRE (JAVA Runtime Environment) or the SDK (Software Development Kit) installed

JAR Files

• Must create a “Manifest” file

• Manifest file tells JAVA which class file inside of your JAR file should be executed

• The format of the manifest file is very strict

Manifest File

• If your JAVA file was called Program6.java, your main class file would be called Program6.class

• The associated manifest file would be :

Main-Class: Program6 <carriage return>

• It is very important that you hit the carriage return at the end of the line!!! (don’t type the word “carriage return” … this simple means to hit “enter” on the keyboard)

JAR Files

• When your JAR file doesn’t work, 9 out of 10 times there is a problem with your manifest file

• Delete your manifest file and try again …

• You can name your manifest file whatever you want … I usually use manifest.txt

Creating the JAR file

• See http://www.cs.fsu.edu/~cis3931/javajar.html for detailed step-by-step instructions.

Thursday’s class…

• Turning a JAVA program into a web-viewable applet

• A few more notes on program 6

• Notes on the “protected”, “private”, “public”, “static”, and “final” modifiers.