Abstract Data Types

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Abstract Data Types

• Linked Lists

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Abstract Data Type(ADT) 4

• ADT--a specification, in abstract terms only,
  without reference to programming language or
  machine dependent terminology.
• ADT--contains two parts
• description of the data together with any
  internal structure that thedata has
• description of the valid operations that can be
  performed on this data

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ADT 2

• Because abstract--can not be used directly in a
  program, but can be implemented into concrete
  instances, which can be used in programs
• To insure conditions that will lead to successful
  application, ADT should make use of the exception
  mechanism

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Ideal properties for ADT List structure
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• should occupy exactly as much memory as necessary
• should be able to grow at any time, and
  accomplish growth quickly
• should be able to shrink at any time and return
  unused memory to the JVM
• should be ordered so that every element has a
  well-defined location.

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ADT List--definition 2

• List--an ordered structure of elements such that
  it is either empty or has a unique first element,
  every element except for the last one has one
  immediate successor, and the last element is that
  one without a successor.
• One element in a non-empty List is always
  designated as the current element.

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ADT List--operations 4

• Create an empty List
• Designate the first element of a non-empty List
  as the current element
• Move the current element to the successor of the
  current element in a non-empty List, unless the
  current element is last
• Insert an element into the List

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ADT List--operations (cont.) 5

• Retrieve the element designated as current,
  unless the List is empty
• Remove the element designated as current, unless
  the List is empty
• Replace the element designated as current, by
  another element unless the List is empty
• Check if the List is empty
• Check if current element is last

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List class--definition 3

• A List is either an empty or sequential structure
  of elements such that one element is always
  designated as current List supports the
  following methods
• constructor creates an empty List containing no
  elements
• public void first() make first element current,
  can only be used on a nonempty List

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List class--definition (cont.) 3

• Public void next() makes the element after the
  current one the (new) current one
• public void insert (Object o) inserts an
  element, or object, into the List
• public Object retrieve()returns current element
  , can only be used on a nonempty List

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List class--definition (cont.) 4

• public void remove () deletes current element
  from the List, only on nonempty
• public void replace (Object o) replaces current
  element by another one, can only be used on a
  nonempty List
• public boolean isEmpty()true if List empty,
  false otherwise
• public boolean isLast()true if element last,
  false otherwise

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Node 3

• A utility class used to create lists and other
  list-like sequential structures
• Need inside a List--a smart obect that can store
  data and knows who its immediate successor, if
  any, is
• Hence, Node has two pieces one piece to store a
  Java object, and another piece to store a
  reference to another Node

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Node (cont.) 3

• A node can return and replace the Object stored
• A node can contain a reference to another node
  called the successor
• Implementation a node can contain two
  non-private fields, one called data that stores
  the actual object and another called next that
  stores either a reference to another node or
  null.

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Node 2

• GO TO node code.
• Draw on board

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Circular node

• (put picture on board)
• Node A new Node()
• Node B new Node()
• Node C new Node()
• A.nextB
• B.nextC
• C.nextA