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Java(TM) 2 Platform, Standard Edition, v1.2.2 API Specification: Class TextField - JDK 5 Documentation v1.2.2, Java 2 SDK 英文文档

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java.awt
Class TextField

java.lang.Object
  |
  +--java.awt.Component
        |
        +--java.awt.TextComponent
              |
              +--java.awt.TextField

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public class TextField

extends TextComponent

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:

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 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);
 

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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.

Since:

JDK1.0

See Also:

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

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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

 

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.
void	addNotify()           Creates the TextField's peer.
boolean	echoCharIsSet()           Indicates whether or not this text field has a character set for echoing.
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 the parameter string representing the state of this text field.
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).
void	setText(String t)           Sets the text that is presented by this text component to be the specified text.

 

Methods inherited from class java.awt.TextComponent

addTextListener, getCaretPosition, getSelectedText, getSelectionEnd, getSelectionStart, getText, isEditable, processTextEvent, removeNotify, removeTextListener, select, selectAll, setCaretPosition, setEditable, setSelectionEnd, setSelectionStart

 

Methods inherited from class java.awt.Component

action, add, addComponentListener, addFocusListener, addInputMethodListener, addKeyListener, addMouseListener, addMouseMotionListener, addPropertyChangeListener, addPropertyChangeListener, bounds, checkImage, checkImage, coalesceEvents, contains, contains, createImage, createImage, deliverEvent, disable, disableEvents, dispatchEvent, doLayout, enable, enable, enableEvents, enableInputMethods, firePropertyChange, getAlignmentX, getAlignmentY, getBackground, getBounds, getBounds, getColorModel, getComponentAt, getComponentAt, getComponentOrientation, getCursor, getDropTarget, getFont, getFontMetrics, getForeground, getGraphics, getHeight, getInputContext, getInputMethodRequests, getLocale, getLocation, getLocation, getLocationOnScreen, getMaximumSize, getName, getParent, getPeer, getSize, getSize, getToolkit, getTreeLock, getWidth, getX, getY, gotFocus, handleEvent, hasFocus, hide, imageUpdate, inside, invalidate, isDisplayable, isDoubleBuffered, isEnabled, isFocusTraversable, isLightweight, isOpaque, isShowing, isValid, isVisible, keyDown, keyUp, layout, list, list, list, list, list, locate, location, lostFocus, mouseDown, mouseDrag, mouseEnter, mouseExit, mouseMove, mouseUp, move, nextFocus, paint, paintAll, postEvent, prepareImage, prepareImage, print, printAll, processComponentEvent, processFocusEvent, processInputMethodEvent, processKeyEvent, processMouseEvent, processMouseMotionEvent, remove, removeComponentListener, removeFocusListener, removeInputMethodListener, removeKeyListener, removeMouseListener, removeMouseMotionListener, removePropertyChangeListener, removePropertyChangeListener, repaint, repaint, repaint, repaint, requestFocus, reshape, resize, resize, setBackground, setBounds, setBounds, setComponentOrientation, setCursor, setDropTarget, setEnabled, setFont, setForeground, setLocale, setLocation, setLocation, setName, setSize, setSize, setVisible, show, show, size, toString, transferFocus, update, validate

 

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

 

Constructor Detail

TextField

public TextField()

Constructs a new text field.

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TextField

public TextField(String text)

Constructs a new text field initialized with the specified text.

Parameters:

text - the text to be displayed. If text is null, the empty string "" will be displayed.

---

TextField

public TextField(int columns)

Constructs a new empty text field with the specified number of columns. A column is an approximate average character width that is platform-dependent.

Parameters:

columns - the number of columns. If columns is less than 0, columns is set to 0.

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TextField

public 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. A column is an approximate average character width that is platform-dependent.

Parameters:

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.

Method Detail

addNotify

public void addNotify()

Creates the TextField's peer. The peer allows us to modify the appearance of the TextField without changing its functionality.

Overrides:

addNotify in class Component

Tags copied from class: Component

See Also:

Component.isDisplayable(), Component.removeNotify()

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getEchoChar

public char getEchoChar()

Gets the character that is to be used for echoing.

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.

Returns:

the echo character for this text field.

See Also:

echoCharIsSet(), setEchoChar(char)

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setEchoChar

public void setEchoChar(char c)

Sets the echo character for this text field.

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.

Parameters:

c - the echo character for this text field.

Since:

JDK1.1

See Also:

echoCharIsSet(), getEchoChar()

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setEchoCharacter

public void setEchoCharacter(char c)

Deprecated. As of JDK version 1.1, replaced by setEchoChar(char).

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setText

public void setText(String t)

Sets the text that is presented by this text component to be the specified text.

Overrides:

setText in class TextComponent

Parameters:

t - the new text.

See Also:

TextComponent.getText()

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echoCharIsSet

public boolean echoCharIsSet()

Indicates whether or not this text field has a character set for echoing.

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.

Returns:

true if this text field has a character set for echoing; false otherwise.

See Also:

setEchoChar(char), getEchoChar()

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getColumns

public int getColumns()

Gets the number of columns in this text field. A column is an approximate average character width that is platform-dependent.

Returns:

the number of columns.

Since:

JDK1.1

See Also:

setColumns(int)

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setColumns

public void setColumns(int columns)

Sets the number of columns in this text field. A column is an approximate average character width that is platform-dependent.

Parameters:

columns - the number of columns.

Throws:

IllegalArgumentException - if the value supplied for columns is less than 0.

Since:

JDK1.1

See Also:

getColumns()

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getPreferredSize

public Dimension getPreferredSize(int columns)

Gets the preferred size of this text field with the specified number of columns.

Parameters:

columns - the number of columns in this text field.

Returns:

the preferred dimensions for displaying this text field.

Since:

JDK1.1

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preferredSize

public Dimension preferredSize(int columns)

Deprecated. As of JDK version 1.1, replaced by getPreferredSize(int).

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getPreferredSize

public Dimension getPreferredSize()

Gets the preferred size of this text field.

Overrides:

getPreferredSize in class Component

Returns:

the preferred dimensions for displaying this text field.

Since:

JDK1.1

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preferredSize

public Dimension preferredSize()

Deprecated. As of JDK version 1.1, replaced by getPreferredSize().

Overrides:

preferredSize in class Component

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getMinimumSize

public Dimension getMinimumSize(int columns)

Gets the minumum dimensions for a text field with the specified number of columns.

Parameters:

columns - the number of columns in this text field.

Since:

JDK1.1

---

minimumSize

public Dimension minimumSize(int columns)

Deprecated. As of JDK version 1.1, replaced by getMinimumSize(int).

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getMinimumSize

public Dimension getMinimumSize()

Gets the minumum dimensions for this text field.

Overrides:

getMinimumSize in class Component

Returns:

the minimum dimensions for displaying this text field.

Since:

JDK1.1

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minimumSize

public Dimension minimumSize()

Deprecated. As of JDK version 1.1, replaced by getMinimumSize().

Overrides:

minimumSize in class Component

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addActionListener

public void addActionListener(ActionListener l)

Adds the specified action listener to receive action events from this text field. If l is null, no exception is thrown and no action is performed.

Parameters:

l - the action listener.

Since:

JDK1.1

See Also:

java.awt.event, removeActionListener(java.awt.event.ActionListener)

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removeActionListener

public void removeActionListener(ActionListener l)

Removes the specified action listener so that it no longer receives action events from this text field. If l is null, no exception is thrown and no action is performed.

Parameters:

l - the action listener.

Since:

JDK1.1

See Also:

java.awt.event, addActionListener(java.awt.event.ActionListener)

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processEvent

protected void processEvent(AWTEvent e)

Processes events on this text field. If the event is an instance of ActionEvent, it invokes the processActionEvent method. Otherwise, it invokes processEvent on the superclass.

Overrides:

processEvent in class TextComponent

Parameters:

e - the event.

Since:

JDK1.1

See Also:

ActionEvent, processActionEvent(java.awt.event.ActionEvent)

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processActionEvent

protected void processActionEvent(ActionEvent e)

Processes action events occurring on this text field by dispatching them to any registered 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:

• An ActionListener object is registered via addActionListener.
• Action events are enabled via enableEvents.

Parameters:

e - the action event.

Since:

JDK1.1

See Also:

ActionListener, addActionListener(java.awt.event.ActionListener), Component.enableEvents(long)

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paramString

protected String paramString()

Returns the parameter string representing the state of this text field. This string is useful for debugging.

Overrides:

paramString in class TextComponent

Returns:

the parameter string of this text field.

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