// ======================================================================== // $Id: LazyList.java,v 1.18 2005/05/12 08:48:20 gregwilkins Exp $ // Copyright 1999-2004 Mort Bay Consulting Pty. Ltd. // ------------------------------------------------------------------------ // Licensed under the Apache License, Version 2.0 (the "License"); // you may not use this file except in compliance with the License. // You may obtain a copy of the License at // http://www.apache.org/licenses/LICENSE-2.0 // Unless required by applicable law or agreed to in writing, software // distributed under the License is distributed on an "AS IS" BASIS, // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. // See the License for the specific language governing permissions and // limitations under the License. // ======================================================================== package org.browsermob.proxy.jetty.util; import java.util.*; /* ------------------------------------------------------------ */ /** Lazy List creation. * A List helper class that attempts to avoid unneccessary List * creation. If a method needs to create a List to return, but it is * expected that this will either be empty or frequently contain a * single item, then using LazyList will avoid additional object * creations by using Collections.EMPTY_LIST or * Collections.singletonList where possible. * * <p><h4>Usage</h4> * <pre> * Object lazylist =null; * while(loopCondition) * { * Object item = getItem(); * if (item.isToBeAdded()) * lazylist = LazyList.add(lazylist,item); * } * return LazyList.getList(lazylist); * </pre> * * An ArrayList of default size is used as the initial LazyList. * * @see java.util.List * @version $Revision: 1.18 $ * @author Greg Wilkins (gregw) */ public class LazyList { private static final String[] __EMTPY_STRING_ARRAY = new String[0]; /* ------------------------------------------------------------ */ private LazyList() {} /* ------------------------------------------------------------ */ /** Add an item to a LazyList * @param list The list to add to or null if none yet created. * @param item The item to add. * @return The lazylist created or added to. */ public static Object add(Object list, Object item) { if (list==null) { if (item instanceof List || item==null) { List l = new ArrayList(); l.add(item); return l; } return item; } if (list instanceof List) { ((List)list).add(item); return list; } List l=new ArrayList(); l.add(list); l.add(item); return l; } /* ------------------------------------------------------------ */ /** Add an item to a LazyList * @param list The list to add to or null if none yet created. * @param index The index to add the item at. * @param item The item to add. * @return The lazylist created or added to. */ public static Object add(Object list, int index, Object item) { if (list==null) { if (index>0 || item instanceof List || item==null) { List l = new ArrayList(); l.add(index,item); return l; } return item; } if (list instanceof List) { ((List)list).add(index,item); return list; } List l=new ArrayList(); l.add(list); l.add(index,item); return l; } /* ------------------------------------------------------------ */ /** Add the contents of a Collection to a LazyList * @param list The list to add to or null if none yet created. * @param collection The Collection whose contents should be added. * @return The lazylist created or added to. * @deprecated Use addCollection */ protected Object add(Object list, Collection collection) { Iterator i=collection.iterator(); while(i.hasNext()) list=LazyList.add(list,i.next()); return list; } /* ------------------------------------------------------------ */ /** Add the contents of a Collection to a LazyList * @param list The list to add to or null if none yet created. * @param collection The Collection whose contents should be added. * @return The lazylist created or added to. */ public static Object addCollection(Object list, Collection collection) { Iterator i=collection.iterator(); while(i.hasNext()) list=LazyList.add(list,i.next()); return list; } /* ------------------------------------------------------------ */ public static Object ensureSize(Object list, int initialSize) { if (list==null) return new ArrayList(initialSize); if (list instanceof ArrayList) return list; List l= new ArrayList(initialSize); l.add(list); return l; } /* ------------------------------------------------------------ */ public static Object remove(Object list, Object o) { if (list==null) return null; if (list instanceof List) { List l = (List)list; l.remove(o); if (l.size()==0) return null; return list; } if (list.equals(o)) return null; return list; } /* ------------------------------------------------------------ */ public static Object remove(Object list, int i) { if (list==null) return null; if (list instanceof List) { List l = (List)list; l.remove(i); if (l.size()==0) return null; return list; } if (i==0) return null; return list; } /* ------------------------------------------------------------ */ /** Get the real List from a LazyList. * * @param list A LazyList returned from LazyList.add(Object) * @return The List of added items, which may be an EMPTY_LIST * or a SingletonList. */ public static List getList(Object list) { return getList(list,false); } /* ------------------------------------------------------------ */ /** Get the real List from a LazyList. * * @param list A LazyList returned from LazyList.add(Object) or null * @param nullForEmpty If true, null is returned instead of an * empty list. * @return The List of added items, which may be null, an EMPTY_LIST * or a SingletonList. */ public static List getList(Object list, boolean nullForEmpty) { if (list==null) return nullForEmpty?null:Collections.EMPTY_LIST; if (list instanceof List) return (List)list; List l = new ArrayList(1); l.add(list); return l; } /* ------------------------------------------------------------ */ public static String[] toStringArray(Object list) { if (list==null) return __EMTPY_STRING_ARRAY; if (list instanceof List) { List l = (List)list; String[] a = new String[l.size()]; for (int i=l.size();i-->0;) { Object o=l.get(i); if (o!=null) a[i]=o.toString(); } return a; } return new String[] {list.toString()}; } /* ------------------------------------------------------------ */ /** The size of a lazy List * @param list A LazyList returned from LazyList.add(Object) or null * @return the size of the list. */ public static int size(Object list) { if (list==null) return 0; if (list instanceof List) return ((List)list).size(); return 1; } /* ------------------------------------------------------------ */ /** Get item from the list * @param list A LazyList returned from LazyList.add(Object) or null * @param i int index * @return the item from the list. */ public static Object get(Object list, int i) { if (list==null) throw new IndexOutOfBoundsException(); if (list instanceof List) return ((List)list).get(i); if (i==0) return list; throw new IndexOutOfBoundsException(); } /* ------------------------------------------------------------ */ public static boolean contains(Object list,Object item) { if (list==null) return false; if (list instanceof List) return ((List)list).contains(item); return list.equals(item); } /* ------------------------------------------------------------ */ public static Object clone(Object list) { if (list==null) return null; if (list instanceof List) return new ArrayList((List)list); return list; } /* ------------------------------------------------------------ */ public static String toString(Object list) { if (list==null) return "[]"; if (list instanceof List) return ((List)list).toString(); return "["+list+"]"; } /* ------------------------------------------------------------ */ public static Iterator iterator(Object list) { if (list==null) return Collections.EMPTY_LIST.iterator(); if (list instanceof List) return ((List)list).iterator(); return getList(list).iterator(); } /* ------------------------------------------------------------ */ public static ListIterator listIterator(Object list) { if (list==null) return Collections.EMPTY_LIST.listIterator(); if (list instanceof List) return ((List)list).listIterator(); return getList(list).listIterator(); } }