[Chapter 8] 8.3 TextArea

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| Chapter 8 Input Fields |

## 8.3 TextArea

`TextArea` is the `TextComponent` for multiline input. Some constructors permit you to set the rows and columns of the `TextArea` on the screen. However, the `LayoutManager` may change your settings. As with `TextField`, the only way to limit the number of characters that a user can enter is to override the `keyDown()` method. The text in a `TextArea` appears left justified, and the justification is not customizable.

In Java 1.1, you can control the appearance of a `TextArea` scrollbar; earlier versions gave you no control over the scrollbars. When visible, the vertical scrollbar is on the right of the `TextArea`, and the horizontal scrollbar is on the bottom. You can remove either scrollbar with the help of several new `TextArea` constants; you can't move them to another side. When the horizontal scrollbar is not present, the text wraps automatically when the user reaches the right side of the `TextArea`. Prior to Java 1.1, there was no way to enable word wrap.

### TextArea Variables

Constants

The constants for `TextArea` are new to Java 1.1; they allow you to control the visibility and word wrap policy of a `TextArea` scrollbar. There is no way to listen for the events when a user scrolls a `TextArea`.

public static final int SCROLLBARS_BOTH

  The `SCROLLBARS_BOTH` mode is the default for `TextArea`. It shows both scrollbars all the time and does no word wrap.

public static final int SCROLLBARS_HORIZONTAL_ONLY

  The `SCROLLBARS_HORIZONTAL_ONLY` mode displays a scrollbar along the bottom of the `TextArea`. When this scrollbar is present, word wrap is disabled.

public static final int SCROLLBARS_NONE

  The `SCROLLBARS_NONE` mode displays no scrollbars around the `TextArea` and enables word wrap. If the text is too long, the `TextArea` displays the lines surrounding the cursor. You can use the cursor to move up and down within the `TextArea`, but you cannot use a scrollbar to navigate. Because this mode has no horizontal scrollbar, word wrap is enabled.

public static final int SCROLLBARS_VERTICAL_ONLY

  The `SCROLLBARS_VERTICAL_ONLY` mode displays a scrollbar along the right edge of the `TextArea`. If the text is too long to display, you can scroll within the area. Because this mode has no horizontal scrollbar, word wrap is enabled.

### TextArea Methods

Constructors

public TextArea ()

  This constructor creates an empty `TextArea` with both scrollbars. The `TextArea` is 0 rows high and 0 columns wide. Depending upon the platform, the `TextArea` could be really small (and useless) or rather large. It is a good idea to use one of the other constructors to control the size of the `TextArea`.

public TextArea (int rows, int columns)

  This constructor creates an empty `TextArea` with both scrollbars. The `TextArea` is `rows` high and `columns` wide.

public TextArea (String text)

  This constructor creates a `TextArea` with an initial content of `text` and both scrollbars. The `TextArea` is 0 rows high and 0 columns wide. Depending upon the platform, the `TextArea` could be really small (and useless) or rather large. It is a good idea to use one of the other constructors to control the size of the `TextArea`.

public TextArea (String text, int rows, int columns)

  This constructor creates a `TextArea` with an initial content of `text`. The `TextArea` is `rows` high and `columns` wide and has both scrollbars.

The following example uses the first four constructors. The results are shown in Figure 8.3. With the size-less constructors, notice that Windows 95 creates a rather large `TextArea`. UNIX systems create a much smaller area. Depending upon the `LayoutManager`, the `TextArea`s could be resized automatically.

    import java.awt.TextArea;
    public class textas extends java.applet.Applet {
        public void init () {
            add (new TextArea ());                     // A
            add (new TextArea (3, 10));                // B
            add (new TextArea ("Empty Area"));         // C
            add (new TextArea ("Empty Area", 3, 10));  // D
        }
    }

#### Figure 8.3: TextArea constructor

public TextArea (String text, int rows, int columns, int scrollbarPolicy)

  The final constructor creates a `TextArea` with an initial content of `text`. The `TextArea` is `rows` high and `columns` wide. The initial scrollbar display policy is designated by the `scrollbarPolicy` parameter and is one of the `TextArea` constants in the previous example. This constructor is the only way provided to change the scrollbar visibility; there is no `setScrollbarVisibility()` method. Figure 8.4 displays the different settings.

#### Figure 8.4: TextArea policies

Setting text

The text-setting methods are usually called in response to an external event. When you handle the insertion position, you must translate it from the visual row and column to a one-dimensional position. It is easier to position the insertion point based upon the beginning, end, or current selection (`getSelectionStart()` and `getSelectionEnd()`).

public void insert (String string, int position)
public void insertText (String string, int position)

  The `insert()` method inserts `string` at `position` into the `TextArea`. If `position` is beyond the end of the `TextArea`, `string` is appended to the end of the `TextArea`.

  `insertText()` is the Java 1.0 name for this method.

public void append (String string)
public void appendText (String string)

  The `append()` method inserts `string` at the end of the `TextArea`.

  `appendText()` is the Java 1.0 name for this method.

public void replaceRange (String string, int startPosition, int endPosition)
public void replaceText (String string, int startPosition, int endPosition)

  The `replaceRange()` method replaces the text in the current `TextArea` from `startPosition` to `endPosition` with `string`. If `endPosition` is before `startPosition`, it may or may not work as expected. (For instance, on a Windows 95 platform, it works fine when the `TextArea` is displayed on the screen. However, when the `TextArea` is not showing, unexpected results happen. Other platforms may vary.) If `startPosition` is 0 and `endPosition` is the length of the contents, this method functions the same as `TextComponent.setText()`.

  `replaceText()` is the Java 1.0 name for this method.

Sizing

public int getRows ()

  The `getRows()` method returns the number of rows set by the constructor or a subsequent call to `setRows()`. This could be different from the displayed height of the `TextArea`.

public void setRows (int rows)

  The `setRows()` method changes the preferred number of rows to display for the `TextField` to `rows`. Because the current `LayoutManager` will do what it wants, the new setting may be ignored. If rows < 0, `setRows()` throws the run-time exception `IllegalArgumentException`.

public int getColumns ()

  The `getColumns()` method returns the number of columns set by the constructor or a subsequent call to `setColumns()`. This could be different from the displayed width of the `TextArea`.

public void setColumns (int columns)

  The `setColumns()` method changes the preferred number of columns to display for the `TextArea` to `columns`. Because the current `LayoutManager` will do what it wants, the new setting may be ignored. If `columns` < 0, `setColumns()` throws the run-time exception `IllegalArgumentException`.

public Dimension getPreferredSize (int rows, int columns)
public Dimension preferredSize (int rows, int columns)

  The `getPreferredSize()` method returns the `Dimension` (width and height) for the preferred size of the `TextArea` with a preferred height of `rows` and width of `columns`. The `rows` and `columns` specified may be different from the current settings.

  `preferredSize()` is the Java 1.0 name for this method.

public Dimension getPreferredSize (int rows, int columns)
public Dimension preferredSize ()

  The `getPreferredSize()` method returns the `Dimension` (width and height) for the preferred size of the `TextArea`. Without the rows and columns parameters, this `getPreferredSize()` uses the constructor's number of rows and columns to calculate the `TextArea`'s preferred size.

  `preferredSize()` is the Java 1.0 name for this method.

public Dimension getMinimumSize (int rows, int columns)
public Dimension minimumSize (int rows, int columns)

  The `getMinimumSize()` method returns the minimum `Dimension` (width and height) for the size of the `TextArea` with a height of `rows` and width of `columns`. The `rows` and `columns` specified may be different from the current settings.

  `minimumSize()` is the Java 1.0 name for this method.

public Dimension getMinimumSize ()
public Dimension minimumSize ()

  The `getMinimumSize()` method returns the minimum `Dimension` (width and height) for the size of the `TextArea`. Without the rows and columns parameters, this `getMinimumSize()` uses the current settings for rows and columns to calculate the `TextArea`'s minimum size.

  `minimumSize()` is the Java 1.0 name for this method.

Miscellaneous methods

public synchronized void addNotify ()

  The `addNotify()` method creates the `TextArea` peer. If you override this method, call `super.addNotify()` first, then add your customizations for the new class. You will then be able to do everything you need with the information about the newly created peer.

public int getScrollbarVisibility()

  The `getScrollbarVisibility()` method retrieves the scrollbar visibility setting, which is set by the constructor. There is no `setScollbarVisibility()` method to change the setting. The return value is one of the `TextArea` constants: `SCROLLBARS_BOTH`, `SCROLLBARS_HORIZONTAL_ONLY`, `SCROLLBARS_NONE`, or `SCROLLBARS_VERTICAL_ONLY`.

protected String paramString ()

  When you call the `toString()` method of `TextArea`, the default `toString()` method of `Component` is called. This in turn calls `paramString()`, which builds up the string to display. The `TextArea` level adds the number of rows and columns for the `TextArea`, and Java 1.1 adds the scrollbar visibility policy. Using `new TextArea(`Empty Area`, 3, 10)`, the results displayed could be:

    java.awt.TextArea[text0,0,0,0x0,invalid,text="Empty Area",
    editable,selection=0-0, rows=3,columns=10, scrollbarVisibility=both]

### TextArea Events

With the 1.0 event model, the `TextArea` component can generate `KEY_PRESS` and `KEY_ACTION` (which calls `keyDown()`) along with `KEY_RELEASE` and `KEY_ACTION_RELEASE` (which called `keyUp()`). There is no `ACTION_EVENT` generated for `TextArea`.

> NOTE:

The `GOT_FOCUS` and `LOST_FOCUS` events can be generated by this component but not reliably across platforms. Currently, they are generated on most UNIX platforms but not on Microsoft Windows NT/95 under Java 1.0. These events are generated under Java 1.1.

Similarly, the mouse events are not generated with JDK 1.0.2. See Appendix C for more information about platform dependencies.

With the Java 1.1 event model, there are no listeners specific to `TextArea`. You can register key, mouse, and focus listeners through the `Component` methods of `addKeyListener()`, `addMouseListener()`, and `addFocusListener()`, respectively. To register listeners for text events, call `TextComponent.addTextListener()`. Action

The `TextArea` component has no way to trigger the action event, since carriage return is a valid character. You would need to put something like a `Button` on the screen to cause an action for a `TextArea`. The following `Rot13` program demonstrates this technique. The user enters text in the `TextArea` and selects the Rotate Me button to rotate the text. If the user selects Rotate Me again, it rotates again, back to the original position. Without the button, there would be no way to trigger the event. Figure 8.5 shows this example in action.

    import java.awt.*;
    public class Rot13 extends Frame {
        TextArea ta;
        Component rotate, done;
        public Rot13 () {
            super ("Rot-13 Example");
            add ("North", new Label ("Enter Text to Rotate:"));
            ta = (TextArea)(add ("Center", new TextArea (5, 40)));
            Panel p = new Panel ();
            rotate = p.add (new Button ("Rotate Me"));
            done = p.add (new Button ("Done"));
            add ("South", p);
        }
        public static void main (String args[]) {
            Rot13 rot = new Rot13();
            rot.pack();
            rot.show();
        }
        public boolean handleEvent (Event e) {
            if (e.id == Event.WINDOW_DESTROY) {
                hide();
                dispose();
                System.exit (0);
                return true;
            }
            return super.handleEvent (e);
        }
        public boolean action (Event e, Object o) {
            if (e.target == rotate) {
                ta.setText (rot13Text (ta.getText()));
                return true;
            } else if (e.target == done) {
                hide();
                dispose();
                System.exit (0);
            }
            return false;
        }
        String rot13Text (String s) {
            int len = s.length();
            StringBuffer returnString = new StringBuffer (len);
            char c;
            for (int i=0;i<len;i++) {
                c = s.charAt (i);
                if (((c >= 'A') && (c <= 'M')) ||
                    ((c >= 'a') && (c <= 'm')))
                    c += 13;
                else if (((c >= 'N') && (c <= 'Z')) ||
                    ((c >= 'n') && (c <= 'z')))
                    c -= 13;
                returnString.append (c);
            }
            return returnString.toString();
        }
    }

#### Figure 8.5: TextArea with activator button

Keyboard

Ordinarily, the `TextArea` component generates all the key events.

public boolean keyDown (Event e, int key)

  The `keyDown()` method is called whenever the user presses a key. `keyDown()` may be called many times in succession if the key remains pressed. `e` is the `Event` instance for the specific event, while `key` is the integer representation of the character pressed. The identifier for the event (`e.id`) for `keyDown()` could be either `Event.KEY_PRESS` for a regular key or `Event.KEY_ACTION` for an action-oriented key (i.e., an arrow or function key). Some of the things you can do through this method are validate input, convert each character to uppercase, and limit the number or type of characters entered. The technique is simple: you just need to remember that the user's keystroke is actually displayed by the `TextArea` peer, which receives the event after the `TextArea` itself. Therefore, a `TextArea` subclass can modify the character displayed by modifying the `key` field (`e.key`) of the `Event` and returning `false`, which passes the `Event` on down the chain; remember that returning `false` indicates that the `Event` has not been completely processed. The following method uses this technique to convert all alphabetic characters to the opposite case:

      public boolean keyDown (Event e, int key) {
          if (Character.isUpperCase ((char)key)) {
              e.key = Character.toLowerCase ((char)key);
          } else if (Character.isLowerCase ((char)key)) {
              e.key = Character.toUpperCase ((char)key);
          }
          return false;
      }

  If `keyDown()` returns `true`, it indicates that the `Event` has been completely processed. In this case, the `Event` never propagates to the peer, and the keystroke is never displayed.

public boolean keyUp (Event e, int key)

  The `keyUp()` method is called whenever the user releases a key. `e` is the `Event` instance for the specific event, while `key` is the integer representation of the character pressed. The identifier for the event (`e.id`) for `keyUp()` could be either `Event.KEY_RELEASE` for a regular key, or `Event.KEY_ACTION_RELEASE` for an action-oriented key (i.e., an arrow or function key).

Mouse

Ordinarily, the `TextArea` component does not trigger any mouse events.

> NOTE:

Mouse events are not generated for `TextArea` with JDK 1.0.2. See Appendix C for more information about platform dependencies.

Focus

The `TextArea` component does not reliably generate focus events.

> NOTE:

The `GOT_FOCUS` and `LOST_FOCUS` events can be generated by this component but not reliably across platforms. With the JDK, they are generated on most UNIX platforms but not on Microsoft Windows NT/95 under JDK 1.0. These events are generated with JDK 1.1. See Appendix C for more information about platform dependencies.

public boolean gotFocus (Event e, Object o)

  The `gotFocus()` method is triggered when the `TextArea` gets the input focus. `e` is the `Event` instance for the specific event, while `o` is a `String` representation of the current contents (`getText()`).

public boolean lostFocus (Event e, Object o)

  The `lostFocus()` method is triggered when the input focus leaves the `TextArea`. `e` is the `Event` instance for the specific event, while `o` is a `String` representation of the current contents (`getText()`).

Listeners and 1.1 event handling

There are no listeners specific to the `TextArea` class. You can register Key, mouse, and focus listeners through the `Component` methods of `addKeyListener()`, `addMouseListener()`, and `addFocusListener()`, respectively. Also, you register listeners for text events by calling `TextComponent.addTextListener()`.

TextField |  | Extending TextField