001: /*
002: * Copyright (c) 2002-2007 JGoodies Karsten Lentzsch. All Rights Reserved.
003: *
004: * Redistribution and use in source and binary forms, with or without
005: * modification, are permitted provided that the following conditions are met:
006: *
007: * o Redistributions of source code must retain the above copyright notice,
008: * this list of conditions and the following disclaimer.
009: *
010: * o Redistributions in binary form must reproduce the above copyright notice,
011: * this list of conditions and the following disclaimer in the documentation
012: * and/or other materials provided with the distribution.
013: *
014: * o Neither the name of JGoodies Karsten Lentzsch nor the names of
015: * its contributors may be used to endorse or promote products derived
016: * from this software without specific prior written permission.
017: *
018: * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
019: * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO,
020: * THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
021: * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR
022: * CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
023: * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
024: * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS;
025: * OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
026: * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
027: * OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE,
028: * EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
029: */
030:
031: package com.jgoodies.binding.extras;
032:
033: import java.beans.PropertyChangeEvent;
034: import java.beans.PropertyChangeListener;
035:
036: import com.jgoodies.binding.value.AbstractValueModel;
037: import com.jgoodies.binding.value.ValueModel;
038:
039: /**
040: * A {@link ValueModel} implementation that avoids <code>null</code> values.
041: * It wraps another ValueModel and returns a (non-null) default value
042: * if the wrapped ValueModel returns null.<p>
043: *
044: * Note that value change events fired by this model may use null
045: * as old and/or new value. This is because PropertyChangeEvents use null
046: * to indicate that the old and/or new value is not provided by the event.<p>
047: *
048: * <strong>Note:</strong> This class is not yet part of the binary Binding
049: * library; it comes with the Binding distributions as an extra.
050: * <strong>The API is work in progress and may change without notice;
051: * this class may even be completely removed from future distributions.</strong>
052: * If you want to use this class, you may consider copying it into
053: * your code base.
054: *
055: * @author Karsten Lentzsch
056: * @version $Revision: 1.6 $
057: *
058: * @since 1.1
059: */
060: public final class NonNullValueModel extends AbstractValueModel {
061:
062: /**
063: * Holds the wrapped subject ValueModel.
064: */
065: private final ValueModel subject;
066:
067: /**
068: * The value returned by this model whenever the
069: * underlying (wrapped) ValueModel returns <code>null</code>.
070: */
071: private final Object defaultValue;
072:
073: // Instance Creation ******************************************************
074:
075: /**
076: * Constructs an NonNullValueModel for the given ValueModel.
077: *
078: * @param subject the underlying (or wrapped) ValueModel
079: * @param defaultValue the value used whenever the wrapped model
080: * returns <code>null</code>
081: *
082: * @throws NullPointerException if the subject or defaultValue is <code>null</code>
083: */
084: public NonNullValueModel(ValueModel subject, Object defaultValue) {
085: this .subject = subject;
086: this .defaultValue = defaultValue;
087: if (defaultValue == null)
088: throw new NullPointerException(
089: "The default value must not be null.");
090:
091: subject.addValueChangeListener(new SubjectValueChangeHandler());
092: }
093:
094: // ValueModel Implementation **********************************************
095:
096: /**
097: * Returns this model's current subject value.
098: *
099: * @return this model's current subject value.
100: */
101: public Object getValue() {
102: Object subjectValue = subject.getValue();
103: return subjectValue != null ? subjectValue : defaultValue;
104: }
105:
106: /**
107: * Sets the given value to the wrapped ValueModel.
108: * The value set can be <code>null</code>.
109: *
110: * @param newValue the value to set
111: */
112: public void setValue(Object newValue) {
113: subject.setValue(newValue);
114: }
115:
116: // Event Handling *********************************************************
117:
118: /**
119: * Forwards value changes in the subject to listeners of this model.
120: * We don't use the default value if the old and/or new value is null.
121: * This is because null has a different meaning in PropertyChangeEvents:
122: * it indicates that the value is not available.
123: */
124: private final class SubjectValueChangeHandler implements
125: PropertyChangeListener {
126:
127: public void propertyChange(PropertyChangeEvent evt) {
128: fireValueChange(evt.getOldValue(), evt.getNewValue(), true);
129: }
130: }
131:
132: }
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