1.2 Exam Only: The java.awt package - Components and Facilities
Write code to demonstrate the use of the following methods of the java.awt.Component class:
setVisible(boolean) , setEnabled(boolean) , getSize() , setForeground()
and setBackground() . |
The names of these methods are self-explanatory. Note that after you create a frame, there are not visible by default, you
must use
setVisible(true)
before it can be seen.
getSize()
returns a dimension
object, which contains two integer member variables,
height
and width
.
Obviously setForeground()
and setBackground()
take a color
argument.
Construct a java.awt.TextArea or java.awt.List that prefers to display a specified number of
columns. |
As there is no mechanism to set the number of columns a list has, I would assume that the above objective contains a typo, and should refer to rows, not columns.
The constructors for a List are as follows:
List(int rows)
Creates a new scrolling list initialized with the specified number of visible lines. By default, multiple selections are not allowed.
List(int rows, boolean multipleMode)
Creates a new scrolling list initialized to display the specified number of rows. If the value ofmultipleMode
istrue
, then the user can select multiple items from the list. If it isfalse
, only one item at a time can be selected.
The constructors for a TextArea are under the next objective.
Construct a java.awt.TextArea or java.awt.TextField that prefers to display a specified
number of columns. |
A TextArea
object is a multi-line region that displays text. The following constructors allow you to specify
the preferred number of rows and columns:
TextArea(int rows, int columns)
Constructs a new empty TextArea with the specified number of rows and columns.
TextArea(String text, int rows, int columns)
Constructs a new text area with the specified text, and with the specified number of rows and columns. This text area is created with both vertical and horizontal scroll bars.
Note: It is the number of rows, then columns. This is counter-intuitive, as usually in programming you specify a horizontal dimension, then a vertical one, so this exception can catch you out.
A TextField
has a single line of text:
TextField(int columns)
Constructs a new empty TextField with the specified number of columns.
TextField(String text, int columns)
Constructs a new text field initialized with the specified text to be displayed, and wide enough to hold the specified number of characters.
State the significance of a "column" where one of the text components is using a proportional (variable) pitch font or a fixed pitch font. |
The width of a "column" is equal to the width of a character, in the particular font being used. In the case of fixed pitch fonts, where all the characters are the same size, this is straightforward. For proportional fonts, the width of a column is equal to the average of the width of all the characters in the font. This means, for example, if you had text component with a proportional font and a width of 10 columns, if you use a narrow letter such as 'i', more than 10 'i's could be displayed.
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