[Chapter 5] 5.2 Labels

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| Chapter 5 Components |

## 5.2 Labels

Having covered the features of the `Component` class, we can now look at some of the simplest components. The first component introduced here is a `Label`. A label is a `Component` that displays a single line of static text.[3] It is useful for putting a title or message next to another component. The text can be centered or justified to the left or right. Labels react to all events they receive. However, they do not get any events from their peers.

> [3] Java in A Nutshell (from O'Reilly & Associates) includes a multiline `Label` component.

### Label Methods

Constants

There are three alignment specifiers for labels. The alignment tells the `Label` where to position its text within the space allotted. Setting an alignment for a `Label` might not do anything noticeable if the `LayoutManager` being used does not resize the `Label` to give it more space. With `FlowLayout`, the alignment is barely noticeable. See Chapter 7, Layouts, for more information.

public final static int LEFT

  `LEFT` is the constant for left alignment. If no alignment is specified in the constructor, left alignment is the default.

public final static int CENTER

  `CENTER` is the constant for center alignment.

public final static int RIGHT

  `RIGHT` is the constant for right alignment.

Constructors

public Label ()

  This constructor creates an empty `Label`. By default, the label's text is left justified.

public Label (String label)

  This constructor creates a `Label` whose initial text is `label`. By default, the label's text is left justified.

public Label (String label, int alignment)

  This constructor creates a `Label` whose initial text is `label`. The alignment of the label is `alignment`. If `alignment` is invalid (not `LEFT`, `RIGHT`, or `CENTER`), the constructor throws the run-time exception `IllegalArgumentException`.

Text

public String getText ()

  The `getText()` method returns the current value of `Label`.

public void setText (String label)

  The `setText()` method changes the text of the `Label` to `label`. If the new label is a different size from the old one, you should revalidate the display to ensure the label's entire contents will be seen.

Alignment

public int getAlignment ()

  The `getAlignment()` method returns the current alignment of the `Label`.

public void setAlignment (int alignment)

  The `setAlignment()` method changes the alignment of the `Label` to `alignment`. If `alignment` is invalid (not `LEFT`, `RIGHT`, or `CENTER`), `setAlignment()` throws the run-time exception `IllegalArgumentException`. Figure 5.2 shows all three alignments.

#### Figure 5.2: Labels with different alignments

Miscellaneous methods

public synchronized void addNotify ()

  The `addNotify()` method creates the `Label` peer. If you override this method, first call `super.addNotify()`, then put in your customizations. Then you will be able to do everything you need with the information about the newly created peer.

protected String paramString ()

  The `paramString()` method overrides `Component`'s `paramString()` method. It is a protected method that calls the overridden `paramString()` to build a `String` from the different parameters of the `Component`. When the method `paramString()` is called for a `Label`, the alignment and label's text are added. Thus, for the `Label` created by the constructor `new Label (`ZapfDingbats`, Label.RIGHT)`, the results displayed from a call to `toString()` would be:

    java.awt.Label[0,0,0x0,invalid,align=right,label=ZapfDingbats]

### Label Events

The `Label` component can react to any event it receives, though the `Label` peer normally does not send any. However, there is nothing to stop you from posting an event yourself.

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