Foundational Data Structures

1
Foundational Data Structures

• B.Ramamurthy
• Chapter 4

2
Introduction

• Array and linked list are the base on which many
  other Abstract Data Types (ADTs) are built.
• Arrays and linked list are called the
  foundational data structures.
• In this discussion we will examine the support
  for arrays in Java language and a number of
  linked list implementation alternatives.

3
Arrays

• In Java an array is an object that contains a
  collection of objects, all of the same type.
• int a new int 5
• allocates 5 integers and assigns it to array
  variable a.

4
Array internal representation
length attribute gives the number of elements in
an array. sizeof(arrayname) gives the storage
needed for the array elements (not including the
length attribute)
Array object
6
length
5
Array Initialization

• At the time of declaration an array can be
  initialized to a set of values.
• Example
• protected final static String courses
  CSE115, CSE116, CSE191, CSE191,
  CSE241, CSE250, CSE305, CSE341,
  CSE396,CSE351, CSE421
• protected JLabel reg1Labels

6
Length Attribute

• Often we want to find the length of a certain for
  processing purposes.
• Use length attribute (or property)
• for (int j 0 j lt reg1Labels.length j)
• regLabelsj new JLabel(coursesj)
• Creates a Jlabel with course names as values.

7
Array Wrapper Class

• Wrapper class is concept is often used when a
  built-in class does not satisfy the needs of a
  development environment.
• Lets examine how to build a Wrapper class Array.
• Class data, constructors, assign method,
  accesors, mutators (resizers), toString and equal.

8
Constructors

• public class Array
• //data
• protected Object data
• protected int base
• // constructors
• public Array (int n, int m)
• data new Objectn
• base m
• public Array() this(0,0)
• public Array (int n) this (n,0)
• // other methods

9
Assign method

• public void assign(Array array)
• if (array ! this)
• if (data.length ! array.data.length)
• data new Objectarray.data.length
• for (int j 0 j lt data.length j)
• data j array.dataj
• base array.base

10
Accessor (methods)

• public Object getData()
• return data // is this good style?
• public int getBase()
• return base
• public int getLength()
• return data.length // is this right?

11
get and put methods

• public Object get (int position )
• return data position -base
• public void put (int position, Object object)
• data position - base object

12
setLength and setBase

• public void setBase (int base)
• this.base base
• public void setLength (int newLength)
• if (data.length ! newLength)
• Object newData new ObjectnewLength
• int min data.lengthlt newLength?
  data.length newLength
• for (int j 0 j lt min j)
• newData j dataj
• data newData

13
Picture It
Array b new Array(6,3)
external
3 4 5 6 7 8
Therefor, actual index is (position - base)
And so on...
internal
14
toString method

• public String toString()
• StringBuffer buf new StringBuffer()
• for(int j 0 j lt data.length j)
• buf.append(String.valueOf(dataj)
• return buf.toString()

15
equal method

• public boolean equal(Array other)
• if (data.length ! other.data.length)
• return false
• else
• int j 0
• while ((j lt data.length) (dataj
  other.dataj))
• j
• if (j data.length) return true
• else return false

16
Multi-dimensional Array

• A multi-dimensional array of dimension n is a
  collection of items which is accessed via
  n-subscript expressions.
• Java language actually supports array of arrays.
• Example
• int x new int35

17
Two dimensional Array Manipulation

• 1. Declare two dimensional array of integers of 4
  rows and 4 columns.
• 2. Initialize the array to all 1s.
• 3. Update the cell contents of the array to the
  sum of the row and column index.
• 4. Make all the diagonal elements 0.
• 5. Flip the contents of row 2 with column 3.

18
Other Variations of Array

• Since Java supports multi-dimensional arrays as
  array of arrays, other shapes such as triangular
  arrays are possible.
• For example how will you declare this?
• 0,0
• 1,01,1
• 2,02,12,2
• 3,03,13,23,3