001package votorola.g.hold; // Copyright 2005-2006, Michael Allan.  Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Votorola Software"), to deal in the Votorola Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicence, and/or sell copies of the Votorola Software, and to permit persons to whom the Votorola Software is furnished to do so, subject to the following conditions: The preceding copyright notice and this permission notice shall be included in all copies or substantial portions of the Votorola Software. THE VOTOROLA SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE VOTOROLA SOFTWARE OR THE USE OR OTHER DEALINGS IN THE VOTOROLA SOFTWARE.
002
003import java.util.*;
004import votorola.g.lang.*;
005
006
007/** A null implementation of a spool.  It is always empty and never unwinds.
008  */
009public final @ThreadSafe class Spool0 extends AbstractCollection<Hold> implements Spool
010{
011
012    private Spool0() {}
013
014
015
016    /** The single instance of Spool0.
017      */
018    public static Spool0 i() { return instance; }
019
020
021        private static final Spool0 instance = new Spool0();
022
023
024
025   // - C o l l e c t i o n --------------------------------------------------------------
026
027
028    public Iterator<Hold> iterator()
029    {
030        List<Hold> emptyList = Collections.emptyList();
031        return emptyList.iterator();
032    }
033
034
035
036    /** Returns zero.
037      */
038    public int size() { return 0; }
039
040
041
042   // - S p o o l ------------------------------------------------------------------------
043
044
045    /** Does nothing and returns true.
046      */
047    public boolean add( Hold hold ) { return true; }
048
049
050
051    /** Returns false.
052      */
053    public boolean isUnwinding() { return false; }
054
055
056
057    /** Does nothing and returns false.
058      */
059    public boolean unwind() { return false; }
060
061
062
063    /** Does nothing and returns false.
064      */
065    public boolean unwind( Catcher<Hold> catcher ) { return false; }
066
067
068}