# 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()`
Creates and returns a copy of this object.
`boolean`
`equals(Object obj)`
Indicates whether some other object is "equal to" this one.
`protected void`
`finalize()`
Deprecated, for removal: This API element is subject to removal in a future version.
Finalization is deprecated and subject to removal in a future release.
`final Class<?>`
`getClass()`
Returns the runtime class of this `Object`.
`int`
`hashCode()`
Returns a hash code value for this object.
`final void`
`notify()`
Wakes up a single thread that is waiting on this object's monitor.
`final void`
`notifyAll()`
Wakes up all threads that are waiting on this object's monitor.
`String`
`toString()`
Returns a string representation of the object.
`final void`
`wait()`
Causes the current thread to wait until it is awakened, typically by being notified or interrupted.
`final void`
`wait(long timeoutMillis)`
Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`
`wait(long timeoutMillis, int nanos)`
Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.

## 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()`