Highlighting a text in JTextArea (JAVA)

Highlighting a text in JTextArea (JAVA):

The following code shows you how you can color/highlight the text in JTextArea, for example all the java reserved words such as “public, private, String” etc. and you want to highlight them in the JTextArea so you do the following:

First Creating a JTextArea:

JTextArea txtArea = new JTextArea();

Now, setting JTextArea size:

txtArea.setPreferredSize(new Dimension(790, 480));

The following String contains all the java reserved words in it that we want to highlight in JTextArea:

String [] javaWords = {"abstract", "do", "import", "public", "throws", "boolean", "double", "instanceof", "return", "transient", "break", "else", " int ", "short","try", "byte", "extends", "interface", "static", "void", "case", "final", "long", "strictfp", "volatile", "catch", "finally", "native", "super", "while", "char", "float","new", "switch", "class", "for", "package", "synchronized", "continue", "if", "private","this", "default", "implements", "protected", "const", "goto", "null", "true", "false"};

The following function highLights function takes two argumenst first JtextComponent and the second String pattern:

// Creates highlights around all occurrences of pattern in textComp

public void highLight(JTextComponent textComp, String[] pattern) {   

  // First remove all old highlights

     removeHighlights(textComp);

  try {

              

     Highlighter hilite = textComp.getHighlighter();                                

     Document doc = textComp.getDocument();      

     String text = doc.getText(0, doc.getLength());         

     for (int i = 0; i < pattern.length; i++) {                          

        int pos = 0;

         // Search for pattern

         while ((pos = text.indexOf(pattern[i], pos)) >= 0) {

                    

            hilite.addHighlight(pos, pos + pattern[i].length(),

                                                myHighlighter);             

            pos += pattern[i].length();

         }

     }

     } catch (BadLocationException e) {}

          

}

The following function removeHighlight removes the highlight from the component:

// Removes only our private highlights

 public void removeHighlights(JTextComponent textComp) {

          

   Highlighter hilite = textComp.getHighlighter();

          

   Highlighter.Highlight[] hilites = hilite.getHighlights();

    for (int i = 0; i < hilites.length; i++) {

          

      if (hilites[i].getPainter() instanceof MyHighlightPainter) {

              

              hilite.removeHighlight(hilites[i]);

      }

   }

}

Now how to call it in your application:

// An instance of the private subclass of the default highlight painter

Highlighter.HighlightPainter myHighlighter = new MyHighlightPainter(Color.LIGHT_GREY);

// A class of the default highlight painter

private class MyHighlightPainter extends DefaultHighlighter.DefaultHighlightPainter {

          

      public MyHighlightPainter(Color color) {

             

            super(color);                

              

       }

}

Now, at keyPress/keyUp event of interface KeyListener and registered it with the JTextArea and call the highLight function to color the reserved words, like this:

txtArea.addKeyListener(new KeyAdapter() {

                    

   public void keyPressed(KeyEvent ke) {

                                                      

         highLight(txtArea, javaWords);                        

                          

  }

                                        

});