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Chapter 9 (part of) Single-dimensional Arrays. Knowledge Goals. Understand the difference between atomic and composite data types Understand the difference between unstructured and structured composite data types Know how Java implements arrays

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Chapter 9 (part of)

Single-dimensional Arrays

knowledge goals
Knowledge Goals
  • Understand the difference between atomic and composite data types
  • Understand the difference between unstructured and structured composite data types
  • Know how Java implements arrays
  • Know how an array is passed as an argument
skill goals
Skill Goals
  • Declare and instantiate a one-dimensional array
  • Access and manipulate the individual components in a one-dimensional array where the elements are
    • Atomic types
    • Composite types
  • Use an initializer list to instantiate a one-dimensional array
java data types1
Java Data Types

Try expressing these definitions in words

java data types2
Java Data Types

Composite data type

A data type that allows a collection of values to be associated with an identifier of that type

Unstructured data type

A collection of components that are not organized with respect to one another

Structured data type

An organized collection of components; the organization determines the means used to access individual components

Is a class structured?

java data types3
Java Data Types

class Example


double field3;

int field2;

int field1;


class Example


int field1;

int field2;

double field3;


Changing the order does not change the access

Is a class structured?

Did you change your answer?

one dimensional arrays
One-Dimensional Arrays

Data structure

The implementation of a composite data type

Note the difference between a data structure (implementation of any composite type) and a structured data type (a composite type that is structured)

one dimensional arrays1
One-Dimensional Arrays

One-dimensional array

A structured collection of components, all of the same type, that is given a single name; each component is accessed by an index that indicates the component's position within the collection


  • composite, unstructured
  • heterogeneous
  • access by field name
  • Array
    • composite, structured
    • homogeneous
    • access by position
one dimensional arrays2
One-Dimensional Arrays



one dimensional arrays3
One-Dimensional Arrays

int[] numbers = new int[4];


type of


can be

stored in

each cell


one dimensional arrays4
One-Dimensional Arrays

float realNumbers[] = new float[10];


do you



into the



one dimensional arrays5
One-Dimensional Arrays

Array Initializers

int numbers[] = {4.93, -15.2, 0.5, 1.67};


do the



storing in

with the


one dimensional arrays6
One-Dimensional Arrays

Accessing Individual Components

Indexing expression

one dimensional arrays7
One-Dimensional Arrays





Place into which

a value is stored;

value is changed

Place from which

a value is extracted;

value is not changed

one dimensional arrays8
One-Dimensional Arrays



if you

try to




one dimensional arrays9
One-Dimensional Arrays

Out-of-bounds array index

An index that is either less than 0 or greater than the array size minus 1, causing an ArrayIndexoutOfBoundsException to be thrown


A public instance variable associated with each instantiated array, accessed by array name .length

Use length to avoid out-of-bounds indexes

one dimensional arrays10
One-Dimensional Arrays

Aggregate Array Operations

What does the following expression return?

numbers == values

one dimensional arrays11
One-Dimensional Arrays

Now, what does the following expression return?

numbers == values

one dimensional arrays12
One-Dimensional Arrays

System provides two useful array methods

first = second.clone(); // duplicates second import java.util.Arrays;

Arrays.equals(first, second); // item-by-item check

System.out.println(first == second);

System.out.println(Arrays.equals(first, second);

What is printed?

more examples
More Examples

What does this code segment do?

totalOccupants = 0;

for (int aptNo = 0; aptNo < occupants.length; aptNo++)

totalOccupants = totalOccupants +occupants[aptNo];

more examples1
More Examples

What does

this code




if ((letter >= 'A' && letter <= 'Z' ||

letter >= 'a' && letter <= 'z'))


index = (int)Character.toUpperCase(letter) - (int)'A';

lettrCount[index] = letterCount[index] + 1;


arrays of objects
Arrays of Objects

String groceryItems[] = new String[10];

for (index = 0; index < grocerItems.length; index++)


groceryItems[index] = inFile.nextLine();


arrays of objects1
Arrays of Objects

Expression Class/Type

groceryItems Reference to an array

groceryItems[0] Reference to a string

groceryItems[0].charAt() A character

groceryItems[10] Error

Base address

The memory address of the first element of the array

"Reference to" is the base address

arrays of objects2
Arrays of Objects

How do Array.equals and clone operate with arrays of objects?

Array.equals uses the == operator to compare arrays, so the addresses are compared

clone uses the = operator, so the addresses are copied

Array.equals(numbers, numbers.clone()) ?

arrays of objects3
Arrays of Objects

Date bigEvents[] = new Date[10];


Expression Class/Type

bigEvents Array

bigEvents[0] Date

bigEvents[0].month String

bigEvents[0].day int

bigEvents[0].year int

bigEvents[0].month.charAt(0) char


[ 0 ]

[ 1 ]




[ 9 ]












arrays of objects4
Arrays of Objects

length is the number of slots assigned to the array

What if the array doesn’t have valid data in each of these slots?

Keep a counter of how many slots have valid data and use this counter when processing the array

More about this type of

processing in Chapter 11

arrays of objects5
Arrays of Objects

public static double average(int grades[])

// Calculates and returns the average grade in an

// array of grades.

// Assumption: All array slots have valid data.


int total = 0;

for (int i = 0; i < grades.length; i++)

total = total + grades[i];

return (double) total / (double) grades.length;


What is passed as an argument?