From 90fe83d282f3f12dce84e4928c8eecb34da34db3 Mon Sep 17 00:00:00 2001 From: Mark Wielaard Date: Tue, 9 Jan 2001 23:06:19 +0000 Subject: * gnu/java/util/DoubleEnumeration.java: new class, adapted from java/util/DoubleEnumeration. Clears references earlier, handles null and/or empty enumerations better. * gnu/java/util/EmptyEnumeration.java: new class. --- gnu/java/util/DoubleEnumeration.java | 128 +++++++++++++++++++++++++++++++++++ gnu/java/util/EmptyEnumeration.java | 77 +++++++++++++++++++++ 2 files changed, 205 insertions(+) create mode 100644 gnu/java/util/DoubleEnumeration.java create mode 100644 gnu/java/util/EmptyEnumeration.java (limited to 'gnu/java/util') diff --git a/gnu/java/util/DoubleEnumeration.java b/gnu/java/util/DoubleEnumeration.java new file mode 100644 index 000000000..33aa2d8e6 --- /dev/null +++ b/gnu/java/util/DoubleEnumeration.java @@ -0,0 +1,128 @@ +/* gnu.java.util.DoubleEnumeration + Copyright (C) 1998, 1999, 2001 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., 59 Temple Place, Suite 330, Boston, MA +02111-1307 USA. + +As a special exception, if you link this library with other files to +produce an executable, this library does not by itself cause the +resulting executable to be covered by the GNU General Public License. +This exception does not however invalidate any other reasons why the +executable file might be covered by the GNU General Public License. */ + +package gnu.java.util; + +import java.io.*; +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.
+ * + * In the default case: + * 
+ * doubleEnum = new DoubleEnumeration(enum1, enum2);
+ * while (doubleEnum.hasMoreElements()) {
+ *    Object o = doubleEnum.nextElement();
+ *    do_something(o);
+ * }
+ *
+ * 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 implements Enumeration +{ + /** + * This is true as long as one of the enumerations has more + * elements. + * Only valid when hasChecked is true. + * Set in hasMoreElements() + */ + private boolean hasMore; + /** + * This is true, if it is sure that hasMore indicates wether there are + * more elements. + * Set to true in hasMoreElements(). + * Set to false in getNextElement(). + */ + private boolean hasChecked; + /** + * The first enumeration. + */ + private Enumeration e1; + /** + * The second enumeration. + */ + private Enumeration e2; + + /** + * Creates a new Enumeration combining the given two enumerations. + * The enumerations mustn't be accessed by other classes. + */ + public DoubleEnumeration(Enumeration e1, Enumeration 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 NoSuchElementException. + */ + public Object nextElement() + { + if (!hasMoreElements()) + throw new NoSuchElementException(); + else { + hasChecked = false; + return e1.nextElement(); + } + } +} diff --git a/gnu/java/util/EmptyEnumeration.java b/gnu/java/util/EmptyEnumeration.java new file mode 100644 index 000000000..5ee11d7d4 --- /dev/null +++ b/gnu/java/util/EmptyEnumeration.java @@ -0,0 +1,77 @@ +/* gnu.java.util.EmptyEnumeration + Copyright (C) 2001 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., 59 Temple Place, Suite 330, Boston, MA +02111-1307 USA. + +As a special exception, if you link this library with other files to +produce an executable, this library does not by itself cause the +resulting executable to be covered by the GNU General Public License. +This exception does not however invalidate any other reasons why the +executable file might be covered by the GNU General Public License. */ + +package gnu.java.util; + +import java.util.Enumeration; +import java.util.NoSuchElementException; + +/** + * This is a helper class that produces an empty Enumerations. + * There is only one instance of this class that can be used whenever one + * needs a non-null but empty enumeration. Using this class prevents multiple + * small objects and inner classes. getInstance() returns + * the only instance of this class. It can be shared by multiple objects and + * threads + *

+ * hasMoreElements() always returns false. + * nextElement() always throws NoSuchElementException. + * + * @author Mark Wielaard (mark@klomp.org) + */ +public final class EmptyEnumeration implements Enumeration { + + /** The only instance of this class */ + private static final EmptyEnumeration instance = new EmptyEnumeration(); + + /** + * Private constructor that creates a new empty Enumeration. + */ + private EmptyEnumeration() { + } + + /** + * Returns the only instance of this class. + * It can be shared by multiple objects and threads. + */ + public static EmptyEnumeration getInstance() { + return instance; + } + + /** + * Always returns false. + */ + public boolean hasMoreElements() { + return false; + } + + /** + * Always throws NoSuchElementException. + */ + public Object nextElement() throws NoSuchElementException { + throw new NoSuchElementException(); + } +} -- cgit v1.2.1