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//
//  ========================================================================
//  Copyright (c) 1995-2016 Mort Bay Consulting Pty. Ltd.
//  ------------------------------------------------------------------------
//  All rights reserved. This program and the accompanying materials
//  are made available under the terms of the Eclipse Public License v1.0
//  and Apache License v2.0 which accompanies this distribution.
//
//      The Eclipse Public License is available at
//      http://www.eclipse.org/legal/epl-v10.html
//
//      The Apache License v2.0 is available at
//      http://www.opensource.org/licenses/apache2.0.php
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//  You may elect to redistribute this code under either of these licenses.
//  ========================================================================
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package org.eclipse.jetty.util;

import java.io.Serializable;
import java.lang.reflect.Array;
import java.util.ArrayList;
import java.util.Collection;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;
import java.util.ListIterator;

/** 
 * Lazy List creation.
 * 

* A List helper class that attempts to avoid unnecessary 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 {@link Collections#EMPTY_LIST} or * {@link Collections#singletonList(Object)} where possible. *

*

* LazyList works by passing an opaque representation of the list in * and out of all the LazyList methods. This opaque object is either * null for an empty list, an Object for a list with a single entry * or an {@link ArrayList} for a list of items. *

* Usage *
 *   Object lazylist =null;
 *   while(loopCondition)
 *   {
 *     Object item = getItem();
 *     if (item.isToBeAdded())
 *         lazylist = LazyList.add(lazylist,item);
 *   }
 *   return LazyList.getList(lazylist);
 * 
* * An ArrayList of default size is used as the initial LazyList. * * @see java.util.List */ @SuppressWarnings("serial") public class LazyList implements Cloneable, Serializable { 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. */ @SuppressWarnings("unchecked") 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. */ @SuppressWarnings("unchecked") 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. */ public static Object addCollection(Object list, Collection collection) { Iterator i=collection.iterator(); while(i.hasNext()) list=LazyList.add(list,i.next()); return list; } /* ------------------------------------------------------------ */ /** Add the contents of an array to a LazyList * @param list The list to add to or null if none yet created. * @param array The array whose contents should be added. * @return The lazylist created or added to. */ public static Object addArray(Object list, Object[] array) { for(int i=0;array!=null && i(initialSize); if (list instanceof ArrayList) { ArrayList ol=(ArrayList)list; if (ol.size()>initialSize) return ol; ArrayList nl = new ArrayList(initialSize); nl.addAll(ol); return nl; } 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. * @param the list entry type */ 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. * @param the list entry type */ @SuppressWarnings("unchecked") public static List getList(Object list, boolean nullForEmpty) { if (list==null) { if (nullForEmpty) return null; return Collections.emptyList(); } if (list instanceof List) return (List)list; return (List)Collections.singletonList(list); } /** * Simple utility method to test if List has at least 1 entry. * * @param list * a LazyList, {@link List} or {@link Object} * @return true if not-null and is not empty */ public static boolean hasEntry(Object list) { if (list == null) return false; if (list instanceof List) return !((List)list).isEmpty(); return true; } /** * Simple utility method to test if List is empty * * @param list * a LazyList, {@link List} or {@link Object} * @return true if null or is empty */ public static boolean isEmpty(Object list) { if (list == null) return true; if (list instanceof List) return ((List)list).isEmpty(); return false; } /* ------------------------------------------------------------ */ 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()}; } /* ------------------------------------------------------------ */ /** Convert a lazylist to an array * @param list The list to convert * @param clazz The class of the array, which may be a primitive type * @return array of the lazylist entries passed in */ public static Object toArray(Object list,Class clazz) { if (list==null) return Array.newInstance(clazz,0); if (list instanceof List) { List l = (List)list; if (clazz.isPrimitive()) { Object a = Array.newInstance(clazz,l.size()); for (int i=0;i)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. * @param the list entry type */ @SuppressWarnings("unchecked") public static E get(Object list, int i) { if (list==null) throw new IndexOutOfBoundsException(); if (list instanceof List) return (E)((List)list).get(i); if (i==0) return (E)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.toString(); return "["+list+"]"; } /* ------------------------------------------------------------ */ @SuppressWarnings("unchecked") public static Iterator iterator(Object list) { if (list==null) { List empty=Collections.emptyList(); return empty.iterator(); } if (list instanceof List) { return ((List)list).iterator(); } List l=getList(list); return l.iterator(); } /* ------------------------------------------------------------ */ @SuppressWarnings("unchecked") public static ListIterator listIterator(Object list) { if (list==null) { List empty=Collections.emptyList(); return empty.listIterator(); } if (list instanceof List) return ((List)list).listIterator(); List l=getList(list); return l.listIterator(); } }