Collections Section Index

A Deque is a double ended queue, allowing inserting and removing from both ends.

The Set returned by newSetFromMap() functions with the same ordering and concurrency characteristics of the map it is based off of. Some Map implementations also have a related Set implement, so u...more

If you pass a Comparator that doesn't implement Serializable into a collection like a TreeMap, that collection will automatically be non-serializable. It is best to flag all Comparator implementat...more

The add() method returns a boolean. If the set did not previously contain the element, true is returned. If the set previoulsy did contain the element, false is returned. Of course, you can also c...more

Typically a Map maps a key to a single value. To have a multimap, the values of a Map should be a List instead. Thus there can be multiple values in the List associated with a single key.more

It depends on what you need to do. The remove() method of an Iterator is the safe way to remove elements from an underlying collection. You can't safely remove elements with a for-each loop. For j...more

Class<String> is the generics way of writing String.class. It allows you to improve type safety.

Class<String> is the generics way of writing String.class. It allows you to improve type safety.

A multimap is a map where a single key can map to multiple values.

A multimap is a map where a single key can map to multiple values. (And a value can be associated with multiple keys.)

Boolean.FALSE < Boolean.TRUE

Several methods of the collection interfaces are considered optional. If an unsupported operation is called, that is when you'll see the UnsupportedOperationException thrown. The javadoc for a col...more

Deque is pronounced like deck, not de-queue.

ArrayDeque offers an array backed deque. LinkedList offers a linked list version. LinkedBlockingDeque offers an optionally bounded blocking version.

Synchronized operations are costly and if you aren't modifying a collection much, it is best not to synchronize all collection accesses. The CopyOnWriteXXX collections avoid concurrent modificatio...more