Collections

Collection is a Java interface for common abstract data types that store multiple items in them.

Sub-Interfaces #

• Lists are indexed sequences with duplication. The two most common types are ArrayLists

  Content Note > This page assumes prior knowledge of Python lists from CS61A or equivalent. Arrays are a very popular data structure...

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  and Linked Lists

  Content Note > This page assumes prior knowledge of linked lists from CS61A or equivalent. I'll assume you have already worked...

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  .
• Sets

  Warning > This page is incomplete. help make it better! Basics A Set stores a collection of values with no duplicates. Sets have...

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  are non-indexed sequences with no duplication. (That is, every value in a set is unique.)
• Maps are key-value pairs. See Hashing and Hash Tables

  Hashing and Hash Tables

  Data Indexed Sets: Introduction So far, we've explored a whole bunch of ways we can store items, but they aren't really...

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  for a description on one common map implementation, the HashMap. All keys in a map must be unique, but values can be duplicated.
• Stacks and Queues

  Stacks and queues are two very common data structures used for a variety of applications from CPU processes to finding...

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  are two ordered collections that have two core behaviors:
  • push(T x): puts x on the top.
  • pop(): Removes the first item. (See the stacks and queues page for more information.)

Common Functions #

• Membership tests contains() and containsAll() that can determine whether or not an element is in the collection.
• size() to get the number of items in the collection.
• isEmpty() returns true if there is nothing in the collection.
• iterator() returns an Iterator object to go through all the values in the collection.
• toArray() converts the collection to a standard Java array.
• Optional functions that aren’t implemented in the interface: add, addAll, clear, remove, removeAll, retainAll (intersection)
  • Throws UnsupportedOperationException if not implemented.