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:

  • Method Details

    • 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.
      Parameters:
      list - the list to grow
      initialSize - the size to grow to
      Returns:
      the new List with new size

    • 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.
      Type Parameters:
      E - the list entry type
      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.
      Type Parameters:
      E - the list entry type
      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
      Type Parameters:
      E - the list entry type
      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)