An Applet With Text Fields

The applet's real estate is the area within the border

Source

import java.applet.*;
import java.awt.*;
import java.awt.event.*;

public class AnAppletWithTextFields extends Applet implements ActionListener {
	public void init() {
		Label label1 = new Label("First text field: ");

		textField1 = new TextField("Hello");

		swapEm = new Button("Swap");
		swapEm.addActionListener(this);

		Label label2 = new Label("Second text field: ");

		textField2 = new TextField("Goodbye");
		textField2.setEditable(false);

		add(label1);
		add(textField1);
		add(swapEm);
		add(label2);
		add(textField2);
	}

	public void actionPerformed(ActionEvent e) {
		String temp = textField1.getText();
		textField1.setText(textField2.getText());
		textField2.setText(temp);
	}

	TextField textField1, textField2;
	Button swapEm;
}

Description and Objective

An applet with some text fields and a button that exchanges their contents.

Shows how to create and work with TextField components
Illustrates use of the Label component

Notes

TextFields

A text field alows for input/display of a single line of text
- There is another text-oriented component, TextArea which provides support for multiple lines of Text
- There is also the Label component which merely displays its text
  - Label is used, as its name implies to label other components
    - you could think of it as the equivalent of a prompt in a console application
    - There is no text box, the label appears to be displayed on the surface of the applet
    - A Label component is purely for display purposes
There are several constructors for TextFields
- A defualt constructor that creates an initially empty text field
- A constructor that allows the specification of an inital value
- A constructor that allows the specification of the number of columns for the field

Using a TextField

Although there are ways of listening to a text field's events, we will simply get and set its contents in response to other events.
- TextFields can generate event such as:
  - When the contents of the text field change
The methods getText and setText of the TextField class retrieve/store the value of the text field.
- The contents of the text field is viewed as a String
- Non-string values (such as integer) must be converted to/from String when storing/retrieving the contents of the field

This Applet's Behavior

The init Method
- Two TextFields boxes and associated Labels are created with initial values
  - The second text field is made read only via the setEditable method
    - Although this prevents the user from modifying the text field, the programmer can do so vua the setText method (see below)
- A button is created and wired up
- The components are laid out
The actionPerformed Method
- The contents of the two text fields are exchanged
  - Notice that the fact that textfield2 is not editable does not prevent the applet from modifying the contents

Things to Do

API work

The TextField and Label classes
- What packages are they in?

Playing With the Applet Place the following applets on the same page:

Add a button to clear out the values of the two fields; and only swap the fields if the first is greater than the second (if the first is less than or equal, display a message on the console).
One of the following two (feel free to do both :) ):
- Somewhat reminiscent of the second applet of the AppletWithParameters assignment: have three editable text fields labelled operand1, operator, and operand2, and a fourth read-only text field labelled result. Have a button labelled Calculate. WHen the button is clicked the appropriate operator is applied to the two operands and the resulting value placed in the result text field. If the operator is invalid, send a message to System.err<.code>
- Look up the TextArea class in the API. Place a text area labelled document, and a text field labelled search for on the applet. Look up the indexOf method for String-- it allows you to look for one string within another (like find of the C++ string). Have a button labelled Search, which when clicked looks for the first occurrence of the search for field in the document area. The resulting (or an indication that it wasn't found) should be displayed in a non-editable text field. (Optional-- investigate the setCaretPosition method of the TextComponent class which is the parent class of TextArea and, in addition to displaying the found position in the text field also sets the caret (i.e., the cursor) to the corresponding position in the document area).