arrays - orange coast collegefaculty.orangecoastcollege.edu/...ch07_arrays_p3.pdf · cs 170 _ java...

CS 170 _ Java Programming - M. Malaty

Chapter 7: Arrays – Slide # 1

JAVA: An Introduction to Problem Solving & Programming, 7th Ed. By Walter Savitch

ISBN-13: 9780133766264 © 2015 Pearson Education, Inc., Upper Saddle River, NJ. All Rights Reserved

Arrays

Chapter 7

Part 3 – Multi-Dimensional Arrays





Agenda

• Array Dimensions

• Multi-dimensional arrays

▪ Basics

▪ Printing elements





First Some Video Tutorials• Matthew Guarnotta:

▪ 2D arrays in Java (9:36)

• CompSci Studio:

▪ Java Beginner Programming Tutorial 34 2D Arrays (6:43)

▪ Java Beginner Programming Tutorial 35 2D Array Grid (7:46)

• in28minutes:

▪ Java 2d array tutorial (9:37)

• MargretPosch

▪ Java Basics – 2D Arrays (14:39)

• 2D + Jagged arrays + Arrays class + toString to print elements

• Jose Vidal:

▪ Java Tic Tac Toe Board Program: 2D Array: Tutorial (8:38)

▪ Advanced topics:

• Uses toString() method, for each loops, constructors, & enum

https://www.youtube.com/watch?v=EVl_NBNKOAA

https://www.youtube.com/watch?v=4xoV8cwuEEM

https://www.youtube.com/watch?v=qWjJM9bFZqE

https://www.youtube.com/watch?v=EM_Dc_AySH0

https://www.youtube.com/watch?v=EOfDGRYDCNc

https://www.youtube.com/watch?v=a3nOfh87Rk8





Array Dimensions

• The arrays we discussed so far are called

one-dimensional arrays

• Syntax review:

1. Declaring and then creating memory

dataType[ ] arrayName;

arrayName = new dataType[arraySize];

2. Declaring and creating memory in one stepdataType[ ] = new dataType[arraySize];





Array Dimensions

• An array that has more than one index is

called multi-dimensional arrays

• An array that has two indexes is called two-

dimensional arrays (2D-Arrays or matrix)

• A 2D-array can be displayed as a two-

dimensional table

• 2D arrays are commonly used in financial and

scientific applications





2D Array Declaration

• Syntax :

1. Declaring and then creating memory

dataType[][] arrayName;

arrayName =

new dataType[rowSize][columnSize];

2. Declaring and creating memory in one step

dataType[][] arrayName = new

dataType[rowSize][columnSize];





2D Arrays Example

• Assume you want to keep the medal count for

a specific Olympics

• How would you create a 2D array that

resembles this?

Gold Silver Bronze

Canada 1 1 0

China 1 0 1

Germany 1 2 0

Russia 2 1 1

USA 3 2 1





2D Arrays Example

• Array declarationint[][] medals = new int[5][3];

or

• Array initialization during declaration int[][] medals = { {1,1,0},

{1,0,1},

{1,2,0},

{2,1,1},

{3,2,1}

}

Gold Silver Bronze

Canada 1 1 0

China 1 0 1

Germany 1 2 0

Russia 2 1 1

USA 3 2 1





2D Arrays Example

• Accessing array elements

▪ How many silver medals did Germany get? System.out.printf(“Germany’s medals: %d”, medals[2][1]);

▪ Change the number of gold medals for Canada to be 2 medals [0][0] = 2;

Gold Silver Bronze

Canada 1 1 0

China 1 0 1

Germany 1 2 0

Russia 2 1 1

USA 3 2 1

0 1 2

0

1

2

3

4





2D Arrays Example

• To get the number of rows & columns, use the length instance variable

• To return the number of rowsSystem.out.print(medals.length);

• To return the number of columns

System.out.print(medals[anyRow].length);

Gold Silver Bronze

Canada 1 1 0

China 1 0 1

Germany 1 2 0

Russia 2 1 1

USA 3 2 1

0 1 2

0

1

2

3

4





2D Arrays

Example

Gold Silver Bronze

Canada 1 1 0

China 1 0 1

Germany 1 2 0

Russia 2 1 1

USA 3 2 1





2D Arrays Exercise

Gold Silver Bronze

Canada 1 1 0

China 1 0 1

Germany 1 2 0

Russia 2 1 1

USA 3 2 1

• Modify the code as follows:

▪ Add two, one-dimensional arrays to

save the countries and medal names

▪ Display the countries to the left and the

medal names at the top of the array

contents

• The output should look like the

figure





2D Arrays Exercise

• How will this array be populated?

int my2DArray [][] = new int [5][3];

for (int row = 0; row < my2DArray.length; ++row)

for (int col = 0; col < my2DArray[row].length; ++col)

my2DArray[row][col] = row + col;





2D Arrays Exercise

• How will this array be populated?

int my2DArray [][] = new int [5][3];



my2DArray[row][col] = row + col;

0 1 2

0 0 1 2

1 1 2 3

2 2 3 4

3 3 4 5

4 4 5 6





Printing a 2D Arrays


{


System.out.print(my2DArray[row][col]+”\t“);

System.out.println();

}

0 1 2

0 0 1 2

1 1 2 3

2 2 3 4

3 3 4 5

4 4 5 6





Printing a 2D Arrays• Exercise:

▪ What is printed if we switch the two for

statements?

▪ What must be changed in the code?

0 1 2

0 0 1 2

1 1 2 3

2 2 3 4

3 3 4 5

4 4 5 6





Printing a 2D Arrays• Exercise: What is printed if we switch the two for

statements?

for (int col = 0; col < my2DArray[1].length; ++col)

{


System.out.print(my2DArray[row][col] + "\t");

System.out.println();

}

0 1 2

0 0 1 2

1 1 2 3

2 2 3 4

3 3 4 5

4 4 5 6





Printing a 2D Arrays• Example: Add rows contents

0 1 2

0 0 1 2

1 1 2 3

2 2 3 4

3 3 4 5

4 4 5 6


{

int sum = 0;


sum += my2DArray[row][col];

System.out.println(“Row “ + row + “: “ + sum);

}





More Array Dimensions

• You can define three-dimensional arrays or n-

dimensional array (can be any number).

• Syntax:

dataType[]...[] arrayName = new dataType[idx1]...[idxn];





More Array Dimensions

• Example: ▪ An array of grades, where there are 40 students, all taking

the same 3 courses, and each course has 10 quizzes int [][][] grades = new int[4][3][2];

▪ Total # element = 4 x 3 x 2 = 24

▪ Read and fill the array of grades

▪ What could be a better names for the indices?

int [][][] grades = new int[4][3][2];

// Read from the user

for (int i = 0; i < 4; ++i)

for (int j = 0; j < 3; ++j)

for (int k = 0; k < 2; ++k)

grades[i][j][k] = input.nextInt();





3-D Array Exercise• Create a program that will enter the values

and displays the contents of the 3-D array.

• Sample Output:





Review: Multidimensional-Array Basics

• Consider this table of values






• We specify the row and column indices for the array to access a specific element

table[3][2] has

a value of 1262






• We can access elements of the table with a nested for loop

• Example:





Multidimensional-

Array Example

Sample

screen

output





Summary

• Multidimensional arrays are implemented as

an array of arrays

• Treat two-dimensional array as a table with

rows and columns

arrays - orange coast collegefaculty.orangecoastcollege.edu/...ch07_arrays_p3.pdf · cs 170 _ java...

Documents