Class InputVerifier

java.lang.Object

javax.swing.InputVerifier

public abstract class InputVerifier
extends Object

This class provides the validation mechanism for Swing components. GUIs often need to ensure that the components are in a valid state before allowing the user to navigate the input focus. To do this, clients create a subclass of InputVerifier and, using JComponent's setInputVerifier method, attach an instance of their subclass to the JComponent which is the source of the focus transfer operation. The InputVerifier also provides the possibility to validate against the target of the focus transfer which may reject the focus. Before focus is transferred from the source Swing component to the target Swing component, the input verifier's shouldYieldFocus(source, target) method is called. Focus is transferred only if that method returns true.

The following example has two text fields, with the first one expecting the string "pass" to be entered by the user. If either that string is entered in the first text field or the second text field contains "accept" string, then the user can advance focus to the second text field by clicking in it or by pressing TAB. However, if another string is entered in the first text field and the second text field does not contain "accept", then the user will be unable to transfer focus to the second text field.

import java.awt.*;
import javax.swing.*;

// This program demonstrates the use of the Swing InputVerifier class.
// It creates two text fields; the first of the text fields expects the
// string "pass" as input, and will allow focus to advance to the second text
// field if either that string is typed in by the user or the second
// field contains "accept" string.

public class VerifierTest extends JFrame {

    public VerifierTest() {
        JTextField field1 = new JTextField("Type \"pass\" here");
        JTextField field2 = new JTextField("or \"accept\" here");
        getContentPane().add(field1, BorderLayout.NORTH);
        getContentPane().add(field2, BorderLayout.SOUTH);

        field1.setInputVerifier(new InputVerifier() {
            public boolean verify(JComponent input) {
               return "pass".equals(((JTextField) input).getText());
            }

            public boolean verifyTarget(JComponent input) {
                return "accept".equals(((JTextField) input).getText());
            }

            public boolean shouldYieldFocus(JComponent source,
                                                         JComponent target) {
                return verify(source) || verifyTarget(target);
            }
        });

        pack();
        setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(VerifierTest::new);
    }
}

Since:

1.3

Constructor Summary

Constructors

Modifier	Constructor	Description
protected	InputVerifier()	Constructor for subclasses to call.

Method Summary

Modifier and Type	Method	Description
boolean	shouldYieldFocus(JComponent input)	Deprecated. use shouldYieldFocus(JComponent, JComponent) instead.
boolean	shouldYieldFocus(JComponent source, JComponent target)	Is called by Swing if this InputVerifier is assigned to the source Swing component to check whether the requested focus transfer from the source to target is allowed.
abstract boolean	verify(JComponent input)	Checks whether the JComponent's input is valid.
boolean	verifyTarget(JComponent target)	Checks whether the target JComponent that will be receiving the focus is ready to accept it.

Methods declared in class Object

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

Modifier and Type	Method	Description
protected Object	clone()	Answers a new instance of the same class as the receiver, whose slots have been filled in with the values in the slots of the receiver.
boolean	equals(Object o)	Compares the argument to the receiver, and answers true if they represent the same object using a class specific comparison.
protected void	finalize()	Deprecated, for removal: This API element is subject to removal in a future version. May cause performance issues, deadlocks and hangs.
final Class<? extends Object>	getClass()	Answers the unique instance of java.lang.Class which represents the class of the receiver.
int	hashCode()	Answers an integer hash code for the receiver.
final void	notify()	Causes one thread which is waiting on the receiver to be made ready to run.
final void	notifyAll()	Causes all threads which are waiting on the receiver to be made ready to run.
String	toString()	Answers a string containing a concise, human-readable description of the receiver.
final void	wait()	Causes the thread which sent this message to be made not ready to run pending some change in the receiver (as indicated by notify or notifyAll).
final void	wait(long time)	Causes the thread which sent this message to be made not ready to run either pending some change in the receiver (as indicated by notify or notifyAll) or the expiration of the timeout.
final void	wait(long time, int frac)	Causes the thread which sent this message to be made not ready to run either pending some change in the receiver (as indicated by notify or notifyAll) or the expiration of the timeout.

Constructor Details

InputVerifier

protected InputVerifier()

Constructor for subclasses to call.

Method Details

verify

public abstract boolean verify(JComponent input)

Checks whether the JComponent's input is valid. This method should have no side effects. It returns a boolean indicating the status of the argument's input.

Parameters:

input - the JComponent to verify

Returns:

true when valid, false when invalid

See Also:

• JComponent.setInputVerifier(InputVerifier)
• JComponent.getInputVerifier()

shouldYieldFocus

@Deprecated(since="9")
public boolean shouldYieldFocus(JComponent input)

Deprecated.

use shouldYieldFocus(JComponent, JComponent) instead.

Calls verify(input) to ensure that the input is valid. This method can have side effects. In particular, this method is called when the user attempts to advance focus out of the argument component into another Swing component in this window. If this method returns true, then the focus is transferred normally; if it returns false, then the focus remains in the argument component.

Parameters:

input - the JComponent to verify

Returns:

true when valid, false when invalid

See Also:

• JComponent.setInputVerifier(InputVerifier)
• JComponent.getInputVerifier()

verifyTarget

public boolean verifyTarget(JComponent target)

Checks whether the target JComponent that will be receiving the focus is ready to accept it. This method should be over-ridden only if it is necessary to validate the target of the focus transfer. This method should have no side effects. It returns a boolean indicating the status of the argument's input.

Implementation Requirements:

By default this method returns true.

Parameters:

target - the target JComponent to verify

Returns:

true when valid, false when invalid

Since:

9

See Also:

• JComponent.setInputVerifier(InputVerifier)
• JComponent.getInputVerifier()

shouldYieldFocus

public boolean shouldYieldFocus(JComponent source,
 JComponent target)

Is called by Swing if this InputVerifier is assigned to the source Swing component to check whether the requested focus transfer from the source to target is allowed. This method can have side effects. If this method returns true, then the focus is transferred normally; if it returns false, then the focus remains in the first argument component.

Implementation Requirements:

The basic implementation of this method returns the conjunction of results obtained from verify(input) and verifyTarget(input) to ensure that both the source and the target components are in valid state.

Parameters:

source - the source JComponent of the focus transfer

target - the target JComponent of the focus transfer

Returns:

true when valid, false when invalid

Since:

9

See Also:

• JComponent.setInputVerifier(InputVerifier)
• JComponent.getInputVerifier()