org.eclipse.jetty.util

Class LazyList

java.lang.Object

org.eclipse.jetty.util.LazyList

All Implemented Interfaces:

Serializable, Cloneable

public class LazyList
extends Object
implements Cloneable, Serializable

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 Collections.EMPTY_LIST or 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 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 Also:

List, Serialized Form

Method Summary

Methods

Modifier and Type	Method and Description
static Object	add(Object list, int index, Object item) Add an item to a LazyList
static Object	add(Object list, Object item) Add an item to a LazyList
static Object	addArray(Object list, Object[] array) Add the contents of an array to a LazyList
static Object	addCollection(Object list, Collection<?> collection) Add the contents of a Collection to a LazyList
static Object	clone(Object list)
static boolean	contains(Object list, Object item)
static Object	ensureSize(Object list, int initialSize) Ensure the capacity of the underlying list.
static <E> E	get(Object list, int i) Get item from the list
static <E> List<E>	getList(Object list) Get the real List from a LazyList.
static <E> List<E>	getList(Object list, boolean nullForEmpty) Get the real List from a LazyList.
static boolean	hasEntry(Object list) Simple utility method to test if List has at least 1 entry.
static boolean	isEmpty(Object list) Simple utility method to test if List is empty
static <E> Iterator<E>	iterator(Object list)
static <E> ListIterator<E>	listIterator(Object list)
static Object	remove(Object list, int i)
static Object	remove(Object list, Object o)
static int	size(Object list) The size of a lazy List
static Object	toArray(Object list, Class<?> clazz) Convert a lazylist to an array
static String	toString(Object list)
static String[]	toStringArray(Object list)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Method Detail

add

public static Object add(Object list,
         Object item)

Add an item to a LazyList

Parameters:

list - The list to add to or null if none yet created.

item - The item to add.

Returns:

The lazylist created or added to.

add

public static Object add(Object list,
         int index,
         Object item)

Add an item to a LazyList

Parameters:

list - The list to add to or null if none yet created.

index - The index to add the item at.

item - The item to add.

Returns:

The lazylist created or added to.

addCollection

public static Object addCollection(Object list,
                   Collection<?> collection)

Add the contents of a Collection to a LazyList

Parameters:

list - The list to add to or null if none yet created.

collection - The Collection whose contents should be added.

Returns:

The lazylist created or added to.

addArray

public static Object addArray(Object list,
              Object[] array)

Add the contents of an array to a LazyList

Parameters:

list - The list to add to or null if none yet created.

array - The array whose contents should be added.

Returns:

The lazylist created or added to.

ensureSize

public static Object ensureSize(Object list,
                int initialSize)

Ensure the capacity of the underlying list.

remove

public static Object remove(Object list,
            Object o)

remove

public static Object remove(Object list,
            int i)

getList

public static <E> List<E> getList(Object list)

Get the real List from a LazyList.

Parameters:

list - A LazyList returned from LazyList.add(Object)

Returns:

The List of added items, which may be an EMPTY_LIST or a SingletonList.

getList

public static <E> List<E> getList(Object list,
                  boolean nullForEmpty)

Get the real List from a LazyList.

Parameters:

list - A LazyList returned from LazyList.add(Object) or null

nullForEmpty - If true, null is returned instead of an empty list.

Returns:

The List of added items, which may be null, an EMPTY_LIST or a SingletonList.

hasEntry

public static boolean hasEntry(Object list)

Simple utility method to test if List has at least 1 entry.

Parameters:

list - a LazyList, List or Object

Returns:

true if not-null and is not empty

isEmpty

public static boolean isEmpty(Object list)

Simple utility method to test if List is empty

Parameters:

list - a LazyList, List or Object

Returns:

true if null or is empty

toStringArray

public static String[] toStringArray(Object list)

toArray

public static Object toArray(Object list,
             Class<?> clazz)

Convert a lazylist to an array

Parameters:

list - The list to convert

clazz - The class of the array, which may be a primitive type

Returns:

array of the lazylist entries passed in

size

public static int size(Object list)

The size of a lazy List

Parameters:

list - A LazyList returned from LazyList.add(Object) or null

Returns:

the size of the list.

get

public static <E> E get(Object list,
        int i)

Get item from the list

Parameters:

list - A LazyList returned from LazyList.add(Object) or null

i - int index

Returns:

the item from the list.

contains

public static boolean contains(Object list,
               Object item)

clone

public static Object clone(Object list)

toString

public static String toString(Object list)

iterator

public static <E> Iterator<E> iterator(Object list)

listIterator

public static <E> ListIterator<E> listIterator(Object list)