Creating Notepad in Java

开发者_如何学GoI am creating a notepad application in Java.I have created the text area also the menus .I have a menu called "EDIT" and under that I have "UPPERCASE"..If i select a particular text and click on "UPPERCASE" ,I want the string to be converted into uppercase. Can anyone tell me how to implement this in Java.

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This can be done by using the following methods:

• JTextArea.getSelectionStart()
• JTextArea.getSelectionEnd()
• JTextArea.getText()
• String.toUpperCase()
• JTextArea.replaceRange()

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String.toUpperCase()

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The String class has toUpperCase() and toLowerCase() methods that you can use. Here's an example:

    System.out.println("Hello World!".toUpperCase());
    // prints "HELLO WORLD!"

    System.out.println("FOO $@&# BAR".toLowerCase());
    // prints "foo $@&# bar"

They also have overloads that takes a java.util.Locale if you need to do locale-specific transformation.

Related questions

• How do I convert strings between uppercase and lowercase in Java?
• Convert typed-in Text to lowercase

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Reminder: String is immutable

String is immutable: you can't invoke a method that will mutate the string instance it's invoked upon. The following is a common beginner's mistake:

    String text = "  blah blah bloop  ";
    text.toUpperCase();
    text.trim();
    System.out.println(text);
    // prints "  blah blah bloop  "

Instead of mutating the instance they're invoked on, these methods return a new instance of String.

    String text = "  blah blah bloop  ";
    text = text.toUpperCase().trim();
    System.out.println(text);
    // prints "BLAH BLAH BLOOP"

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Well, JTextArea has a getText and a setText method and String has a toUpperCase method. Check out this example: http://www.exampledepot.com/egs/javax.swing.text/ta_EditTextArea.html

EDIT:

This might work:

JTextArea textArea = new JTextArea("some text");
int start = textArea.getSelectionStart();
int end = textArea.getSelectionEnd();
String replace = textArea.getSelectedText().toUpperCase();
textArea.replaceRange(replace, start, end); 

EIDT 2:

Here is a working example:

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JTextArea;

public class Test {

JTextArea textArea = new JTextArea("some text");

public Test() {

    JButton button = new JButton("upper");
    button.addActionListener(new ActionListener(){
        public void actionPerformed(ActionEvent e) {
            int start = textArea.getSelectionStart();
            int end = textArea.getSelectionEnd();
            String replace = textArea.getSelectedText().toUpperCase();
            textArea.replaceRange(replace, start, end);
        }
    });

    JFrame frame = new JFrame();
    frame.add(textArea);
    frame.add(button, BorderLayout.SOUTH);
    frame.setSize(100, 100);
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
}

public static void main(String[] args) {
    new Test();
}
}

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Swing uses Actions for this type of processing. Functions like cut, copy, paste, select word are all done by Actions. Create your own custom action:

class UpperCaseAction extends TextAction
{
    public UpperCaseAction()
    {
        super("UpperCase");
    }

    public void actionPerformed(ActionEvent e)
    {
        JTextComponent component = getFocusedComponent();
        int start = cmoponent.getSelectionStart();
        int end = component.getSelectionEnd();
        String replace = component.getSelectedText().toUpperCase();
        component.replaceRange(replace, start, end);
    }
}

The benefit of the Action is that it will work on any text component that has focus. You use the Action like:

Action action = new UpperCaseAction();
JMenuItem menuItem = new JMenuItem( action );
JButton button = new JButton( action ); 

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It's much easier if you just send the text to a variable, change it to uppercase and then send it back.

string upper = JTextArea.Text;
upper.toUpperCase();
JTextArea.Text = upper;

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I have faster trick. In this menu item listener u can write:

String selectedText=jTextArea1.getSelectedText();
       if (selectedText==null)return;
       selectedText=selectedText.toUpperCase();
       jTextArea1.replaceSelection(selectedText);