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author | upstream source tree <ports@midipix.org> | 2015-03-15 20:14:05 -0400 |
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committer | upstream source tree <ports@midipix.org> | 2015-03-15 20:14:05 -0400 |
commit | 554fd8c5195424bdbcabf5de30fdc183aba391bd (patch) | |
tree | 976dc5ab7fddf506dadce60ae936f43f58787092 /libjava/classpath/gnu/java/util/DoubleEnumeration.java | |
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Diffstat (limited to 'libjava/classpath/gnu/java/util/DoubleEnumeration.java')
-rw-r--r-- | libjava/classpath/gnu/java/util/DoubleEnumeration.java | 138 |
1 files changed, 138 insertions, 0 deletions
diff --git a/libjava/classpath/gnu/java/util/DoubleEnumeration.java b/libjava/classpath/gnu/java/util/DoubleEnumeration.java new file mode 100644 index 000000000..852644bc6 --- /dev/null +++ b/libjava/classpath/gnu/java/util/DoubleEnumeration.java @@ -0,0 +1,138 @@ +/* gnu.java.util.DoubleEnumeration + Copyright (C) 1998, 1999, 2001, 2004 Free Software Foundation, Inc. + +This file is part of GNU Classpath. + +GNU Classpath is free software; you can redistribute it and/or modify +it under the terms of the GNU General Public License as published by +the Free Software Foundation; either version 2, or (at your option) +any later version. + +GNU Classpath is distributed in the hope that it will be useful, but +WITHOUT ANY WARRANTY; without even the implied warranty of +MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU +General Public License for more details. + +You should have received a copy of the GNU General Public License +along with GNU Classpath; see the file COPYING. If not, write to the +Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA +02110-1301 USA. + +Linking this library statically or dynamically with other modules is +making a combined work based on this library. Thus, the terms and +conditions of the GNU General Public License cover the whole +combination. + +As a special exception, the copyright holders of this library give you +permission to link this library with independent modules to produce an +executable, regardless of the license terms of these independent +modules, and to copy and distribute the resulting executable under +terms of your choice, provided that you also meet, for each linked +independent module, the terms and conditions of the license of that +module. An independent module is a module which is not derived from +or based on this library. If you modify this library, you may extend +this exception to your version of the library, but you are not +obligated to do so. If you do not wish to do so, delete this +exception statement from your version. */ + +package gnu.java.util; + +import java.util.Enumeration; +import java.util.NoSuchElementException; + + +/** + * This is a helper class that combines two Enumerations. + * It returns the elements of the first Enumeration until it has + * no more elements and then returns the elements of the second + * Enumeration.<br> + * + * In the default case: + * <pre> + * doubleEnum = new DoubleEnumeration(enum1, enum2); + * while (doubleEnum.hasMoreElements()) { + * Object o = doubleEnum.nextElement(); + * do_something(o); + * } + * </pre> + * it calls hasMoreElements of the Enumerations as few times as + * possible. + * The references to the Enumerations are cleared as soon as they have no + * more elements to help garbage collecting. + * + * @author Jochen Hoenicke + * @author Mark Wielaard (mark@klomp.org) + */ +public class DoubleEnumeration<T> implements Enumeration<T> +{ + /** + * This is true as long as one of the enumerations has more + * elements. + * Only valid when hasChecked is true. + * Set in <code>hasMoreElements()</code> + */ + private boolean hasMore; + /** + * This is true, if it is sure that hasMore indicates wether there are + * more elements. + * Set to true in <code>hasMoreElements()</code>. + * Set to false in <code>getNextElement()</code>. + */ + private boolean hasChecked; + /** + * The first enumeration. + */ + private Enumeration<T> e1; + /** + * The second enumeration. + */ + private Enumeration<T> e2; + + /** + * Creates a new Enumeration combining the given two enumerations. + * The enumerations mustn't be accessed by other classes. + */ + public DoubleEnumeration(Enumeration<T> e1, Enumeration<T> e2) + { + this.e1 = e1; + this.e2 = e2; + hasChecked = false; + } + + /** + * Returns true, if at least one of the two enumerations has more + * elements. + */ + public boolean hasMoreElements() + { + if (hasChecked) + return hasMore; + + hasMore = (e1 != null && e1.hasMoreElements()); + + if (!hasMore) { + e1 = e2; + e2 = null; + hasMore = (e1 != null && e1.hasMoreElements()); + } + + hasChecked = true; + return hasMore; + } + + /** + * Returns the next element. This returns the next element of the + * first enumeration, if it has more elements, otherwise the next + * element of the second enumeration. If both enumeration don't have + * any elements it throws a <code>NoSuchElementException</code>. + */ + public T nextElement() + { + if (!hasMoreElements()) + throw new NoSuchElementException(); + else { + hasChecked = false; + return e1.nextElement(); + } + } +} |