Collections

Lists

Collections.emptyList() gives an empty list.

There are Lists and Lists.

Lists.newArrayList used to create.

Deletion

The subList() method can be used to delete part of a list. The method eliminates the need for explicit range operations (of the sort that commonly exist for arrays). Any operation that expects a list can be used as a range operation by passing a subList view instead of a whole list. For example, the following idiom removes a range of elements from a list:

list.subList(from, to).clear();

Sets

API

contains()

Returns true if and only if this set contains an element e such that (o==null ? e==null : o.equals(e)).

Tree Sets

java.util.TreeSet<E>

This is a NavigableSet implementation based on a TreeMap. The elements are ordered using their natural ordering or by a Comparator provided at set creation time. This implementation guarantees a log(n) time cost for the basic operations (add, remove and contains).

Maps

Tree Maps

java.until.TreeMap<K, V>

Sorted in a similar manner to the TreeSet.

TreeMap is a SortedMap.

SetMultiMap

// TODO

Maps

Map<K,Collection<V>>

HashMaps

HashMaps and null

When a null is passed as a key to a HashMap it is handled as a special case:

put() and get()

A null key is put in bucket 0 and the value passed into the method is put as the value. This means that the get() method then returns the value in bucket 0

LinkedHashMap

LinkedHashMap<K,V>

// TODO

MultiMap

MultiMap<K,V>

An object that maps keys to collections of values. It extends Map, adding a few new methods that accept values of V directly, rather than values of Collection.

ListMultiMap

A Guava class.

A MultiMap that can hold duplicate key-value pairs and that maintains the insertion ordering of values for a given key.