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Programming in Java Netbeans - A Step by Step Tutorial for Beginners: Lesson 45

Danson Wachira is a certified Trainer in Computer Science, Information Technology and related studies.

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Lesson 45: How to open files using Java Open File dialog box

Welcome to Lesson 45 of programming in Java NetBeans. Over the previous two lessons, we looked at how we can implement the Java Open dialog box so that we can choose files to be opened in the computer. We learnt further that Java Open dialog box can be customized to open only certain types of files using files filter.

In this particular lesson, we shall continue from where we left on Java Open dialog box and we shall discuss how we can use the Open dialog box to actually open a file from the computer. For the practical part of this lesson, we shall use the “TextFiles” project we had in Lesson 34. If you have not done Lesson 34, you will need to take it first before this lesson.

programming-in-java-netbeans-a-step-by-step-tutorial-for-beginners-lesson-45

What we’ll do in this lesson is to import the “TextFiles” class so that we can use it to open a file. The code contained in the “TextFiles” class is the same for opening a file.

To import the “TextFiles” class into the current class, navigate on the Projects window to the current project. Expand the class, right click on its Libraries and select “Add Project” as shown below:

How to import a class into a project in Java NetBeans

programming-in-java-netbeans-a-step-by-step-tutorial-for-beginners-lesson-45

Selecting “Add Project” will activate a dialog box as shown below. The dialog box might look slightly different depending on your computer but make sure the Look in tab is showing the location of your projects.

programming-in-java-netbeans-a-step-by-step-tutorial-for-beginners-lesson-45

Form the above dialog box, scroll to the “TextFiles” class and click on it, the Project JAR Files tab to the right of the window should display the TextFile Jar file available. Click the Add Project JAR Files button so that the Class is added under the current project libraries.

programming-in-java-netbeans-a-step-by-step-tutorial-for-beginners-lesson-45

We have just added classes from the textfile package to our current project. For us to be able to access the member classes and use them, we use the keyword import. We need to use the ReadFile class so add the following line of code to your program:

import textfiles.ReadFile;

The above statement is importing the ReadFile class so that we can use it to read a file. We need to create the object of this class first. We create the object using the following statement:

ReadFile file_read = new ReadFile( file_name ); //Type as one line

Now, what we need to do is to modify our form so that we can have a text area control to display the content of the opened file. Add a text area onto the form. Change the variable name of the text area to txtShow, we’ll use this name later in the code. The form should look as shown below when run:

Scroll to Continue
programming-in-java-netbeans-a-step-by-step-tutorial-for-beginners-lesson-45

In the code stub for Open menu option, type or copy and paste the following code, notice that we have moved the JOption Pane statement into the catch part of the try…catch block for error handling if any.

Code in the stub for Open menu option

FileFilter ft = new FileNameExtensionFilter("Text Files   .txt", "txt");
fc.addChoosableFileFilter(ft);
FileFilter ft2 = new FileNameExtensionFilter("Word Documents   .doc", "doc");
fc.addChoosableFileFilter(ft2);
FileFilter ft3 = new FileNameExtensionFilter("PowerPoint   .ppt", "ppt");
fc.addChoosableFileFilter(ft3);
FileFilter ft4 = new FileNameExtensionFilter("JPEG Images   .jpeg", "jpeg");
fc.addChoosableFileFilter(ft4);
FileFilter ft5 = new FileNameExtensionFilter("Excel Worksheets   .xsl", "xsl");
fc.addChoosableFileFilter(ft5);

int returnVal = fc.showOpenDialog(this);
if (returnVal == javax.swing.JFileChooser.APPROVE_OPTION) {
    java.io.File file = fc.getSelectedFile( );
    String file_name = file.toString( );
    try{
        ReadFile file_read = new ReadFile( file_name ); //Create new object
        String[]arylines = file_read.OpenFile();
        int i;
        String ReadText = "";
        for(i = 0; i < arylines.length; i++){ //Loop through as you read text lines
            ReadText = ReadText + arylines[i] + '\n';
        }
        txtShow.setText(ReadText); //Display text on text area
    }
    catch (java.io.IOException e){ //Handle any error here
         JOptionPane.showMessageDialog(this, e.getMessage());
    }
  }
}   

The above code is just like the code we had for reading a file. We are creating an object of the Readfile class which will call the OpenFile() method to return all the lines of a given text file as an array. Using the FOR loop, we are reading this lines and displaying the text on the text area. Run the form, select any text file through File >> Open option and this time you should be able to display the content of the text file in the text area.

programming-in-java-netbeans-a-step-by-step-tutorial-for-beginners-lesson-45

As you can see, we are able to display the content of any text file in a text area. Open dialog box has a lot of uses in programming and as a GUI control, it help users to access files easily. In the next lesson, we shall look at the Java Save dialog box and how to implement the Save dialog box on Java NetBeans.

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Comments

Felex on April 03, 2013:

Great and very useful Java tutorial!!!!!

Colly on March 19, 2013:

Very good Java tutorial, you have helped me a lot. Thank you!!!

Danson Wachira (author) from Nairobi, Kenya on March 10, 2013:

Hi teaches12345,

I keep on writing these programming articles and i find they keep on asking for more so i have to write more. Thanks for the visit and positive comment.

Dianna Mendez on March 10, 2013:

Excellent lesson. I imagine many people following your advice out there and always finding help from your detailed hubs.

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