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java.lang.Object java.awt.Component java.awt.TextComponent java.awt.TextField
A TextField
object is a text component
that allows for the editing of a single line of text.
For example, the following image depicts a frame with four
text fields of varying widths. Two of these text fields
display the predefined text "Hello"
.
Here is the code that produces these four text fields:
TextField tf1, tf2, tf3, tf4; // a blank text field tf1 = new TextField(); // blank field of 20 columns tf2 = new TextField("", 20); // predefined text displayed tf3 = new TextField("Hello!"); // predefined text in 30 columns tf4 = new TextField("Hello", 30);
Every time the user types a key in the text field, one or
more key events are sent to the text field. A KeyEvent
may be one of three types: keyPressed, keyReleased, or keyTyped.
The properties of a key event indicate which of these types
it is, as well as additional information about the event,
such as what modifiers are applied to the key event and the
time at which the event occurred.
The key event is passed to every KeyListener
or KeyAdapter
object which registered to receive such
events using the component's addKeyListener
method.
(KeyAdapter
objects implement the
KeyListener
interface.)
It is also possible to fire an ActionEvent
.
If action events are enabled for the text field, they may
be fired by pressing the Return
key.
The TextField
class's processEvent
method examines the action event and passes it along to
processActionEvent
. The latter method redirects the
event to any ActionListener
objects that have
registered to receive action events generated by this
text field.
Clarifications
TextField
echo
character are therefore requests (not directives) which may or may
not be honored, and the echo character actually in use may be
different than what is reported by getEchoChar
..
See:
KeyEvent
,
KeyAdapter
,
KeyListener
,
ActionEvent
,
Component.addKeyListener(java.awt.event.KeyListener)
,
processEvent(java.awt.AWTEvent)
,
processActionEvent(java.awt.event.ActionEvent)
,
addActionListener(java.awt.event.ActionListener)
,
Serialized Form
Field Summary |
Fields inherited from class java.awt.TextComponent |
textListener |
Fields inherited from class java.awt.Component |
BOTTOM_ALIGNMENT, CENTER_ALIGNMENT, LEFT_ALIGNMENT, RIGHT_ALIGNMENT, TOP_ALIGNMENT |
Fields inherited from interface java.awt.image.ImageObserver |
ABORT, ALLBITS, ERROR, FRAMEBITS, HEIGHT, PROPERTIES, SOMEBITS, WIDTH |
Constructor Summary | |
TextField()
Constructs a new text field. |
|
TextField(int columns)
Constructs a new empty text field with the specified number of columns. |
|
TextField(String text)
Constructs a new text field initialized with the specified text. |
|
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 columns. |
Method Summary | |
void |
addActionListener(ActionListener l)
Adds the specified action listener to receive action events from this text field. |
boolean |
echoCharIsSet()
Indicates whether or not this text field has a character set for echoing. |
ActionListener[] |
getActionListeners()
Returns an array of all the action listeners registered on this textfield. |
int |
getColumns()
Gets the number of columns in this text field. |
char |
getEchoChar()
Gets the character that is to be used for echoing. |
Dimension |
getMinimumSize()
Gets the minumum dimensions for this text field. |
Dimension |
getMinimumSize(int columns)
Gets the minumum dimensions for a text field with the specified number of columns. |
Dimension |
getPreferredSize()
Gets the preferred size of this text field. |
Dimension |
getPreferredSize(int columns)
Gets the preferred size of this text field with the specified number of columns. |
Dimension |
minimumSize()
Deprecated. As of JDK version 1.1, replaced by getMinimumSize() . |
Dimension |
minimumSize(int columns)
Deprecated. As of JDK version 1.1, replaced by getMinimumSize(int) . |
protected String |
paramString()
Returns a string representing the state of this TextField . |
Dimension |
preferredSize()
Deprecated. As of JDK version 1.1, replaced by getPreferredSize() . |
Dimension |
preferredSize(int columns)
Deprecated. As of JDK version 1.1, replaced by getPreferredSize(int) . |
protected void |
processActionEvent(ActionEvent e)
Processes action events occurring on this text field by dispatching them to any registered ActionListener objects. |
protected void |
processEvent(AWTEvent e)
Processes events on this text field. |
void |
removeActionListener(ActionListener l)
Removes the specified action listener so that it no longer receives action events from this text field. |
void |
setColumns(int columns)
Sets the number of columns in this text field. |
void |
setEchoChar(char c)
Sets the echo character for this text field. |
void |
setEchoCharacter(char c)
Deprecated. As of JDK version 1.1, replaced by setEchoChar(char) . |
Methods inherited from class java.awt.TextComponent |
addTextListener, enableInputMethods, getBackground, getCaretPosition, getSelectedText, getSelectionEnd, getSelectionStart, getText, getTextListeners, isEditable, processTextEvent, removeTextListener, select, selectAll, setCaretPosition, setEditable, setSelectionEnd, setSelectionStart, setText |
Methods inherited from class java.lang.Object |
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait |
Constructor Detail |
public TextField() throws HeadlessException
HeadlessException
- if GraphicsEnvironment.isHeadless()
returns true.GraphicsEnvironment.isHeadless()
public TextField(String text) throws HeadlessException
text
- the text to be displayed. If
text
is null
, the empty
string ""
will be displayed.
HeadlessException
- if GraphicsEnvironment.isHeadless()
returns true.GraphicsEnvironment.isHeadless()
public TextField(int columns) throws HeadlessException
columns
- the number of columns. If
columns
is less than 0
,
columns
is set to 0
.
HeadlessException
- if GraphicsEnvironment.isHeadless()
returns true.GraphicsEnvironment.isHeadless()
public TextField(String text, int columns) throws HeadlessException
text
- the text to be displayed. If
text
is null
, the empty
string ""
will be displayed.columns
- the number of columns. If
columns
is less than 0
,
columns
is set to 0
.
HeadlessException
- if GraphicsEnvironment.isHeadless()
returns true.GraphicsEnvironment.isHeadless()
Method Detail |
public char getEchoChar()
An echo character is useful for text fields where
user input should not be echoed to the screen, as in
the case of a text field for entering a password.
If echoChar
= 0
, user
input is echoed to the screen unchanged.
echoCharIsSet()
,
setEchoChar(char)
public void setEchoChar(char c)
An echo character is useful for text fields where
user input should not be echoed to the screen, as in
the case of a text field for entering a password.
Setting echoChar
= 0
allows
user input to be echoed to the screen again.
c
- the echo character for this text field.echoCharIsSet()
,
getEchoChar()
public void setEchoCharacter(char c)
setEchoChar(char)
.
public boolean echoCharIsSet()
An echo character is useful for text fields where user input should not be echoed to the screen, as in the case of a text field for entering a password.
true
if this text field has
a character set for echoing;
false
otherwise.setEchoChar(char)
,
getEchoChar()
public int getColumns()
setColumns(int)
public void setColumns(int columns)
columns
- the number of columns.
IllegalArgumentException
- if the value
supplied for columns
is less than 0
.getColumns()
public Dimension getPreferredSize(int columns)
columns
- the number of columns
in this text field.
public Dimension preferredSize(int columns)
getPreferredSize(int)
.
public Dimension getPreferredSize()
getPreferredSize
in class Component
Component.getMinimumSize()
,
LayoutManager
public Dimension preferredSize()
getPreferredSize()
.
preferredSize
in class Component
public Dimension getMinimumSize(int columns)
columns
- the number of columns in
this text field.public Dimension minimumSize(int columns)
getMinimumSize(int)
.
public Dimension getMinimumSize()
getMinimumSize
in class Component
Component.getPreferredSize()
,
LayoutManager
public Dimension minimumSize()
getMinimumSize()
.
minimumSize
in class Component
public void addActionListener(ActionListener l)
l
- the action listener.removeActionListener(java.awt.event.ActionListener)
,
getActionListeners()
,
ActionListener
public void removeActionListener(ActionListener l)
l
- the action listener.addActionListener(java.awt.event.ActionListener)
,
getActionListeners()
,
ActionListener
public ActionListener[] getActionListeners()
ActionListener
s
or an empty array if no action
listeners are currently registeredaddActionListener(java.awt.event.ActionListener)
,
removeActionListener(java.awt.event.ActionListener)
,
java.awt.event
protected void processEvent(AWTEvent e)
ActionEvent
,
it invokes the processActionEvent
method. Otherwise, it invokes processEvent
on the superclass.
Note that if the event parameter is null
the behavior is unspecified and may result in an
exception.
processEvent
in class TextComponent
e
- the eventActionEvent
,
processActionEvent(java.awt.event.ActionEvent)
protected void processActionEvent(ActionEvent e)
ActionListener
objects.
This method is not called unless action events are enabled for this component. Action events are enabled when one of the following occurs:
ActionListener
object is registered
via addActionListener
.
enableEvents
.
Note that if the event parameter is null
the behavior is unspecified and may result in an
exception.
e
- the action eventActionListener
,
addActionListener(java.awt.event.ActionListener)
,
Component.enableEvents(long)
protected String paramString()
TextField
.
This method is intended to be used only for debugging purposes, and the
content and format of the returned string may vary between
implementations. The returned string may be empty but may not be
null
.
paramString
in class TextComponent
|
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