MULTIDIMENSIONAL ARRAYS - Introduction to Java Programming - page 281

C HAPTER S UMMARY
1.

A two-dimensional array can be used to store a table.

2.

A variable for two-dimensional arrays can be declared using the syntax:
elementType[][] arrayVar .

3.

A two-dimensional array can be created using the syntax: new elementType
[ROW_SIZE][COLUMN_SIZE] .

4.

Each element in a two-dimensional array is represented using the syntax:
arrayVar[rowIndex][columnIndex] .

5.

You can create and initialize a two-dimensional array using an array initializer with the
syntax: elementType[][] arrayVar = {{row values}, . . . , {row values}} .

6.

You can use arrays of arrays to form multidimensional arrays. For example, a variable
for three-dimensional arrays can be declared as elementType[][][] arrayVar , and
a three-dimensional array can be created using new elementType[size1][size2]
[size3] .

T EST Q UESTIONS

Do the test questions for this chapter online at www.cs.armstrong.edu/liang/intro9e/test.html .

P ROGRAMMING E XERCISES

*7.1

( Sum elements column by column ) Write a method that returns the sum of all the
elements in a specified column in a matrix using the following header:

public static double sumColumn( double [][] m, int columnIndex)

Write a test program that reads a 3-by-4 matrix and displays the sum of each col-
umn. Here is a sample run:

Enter a 3-by-4 matrix row by row:

1.5 2 3 4

5.5 6 7 8

9.5 1 3 1

Sum of the elements at column 0 is 16.5
Sum of the elements at column 1 is 9.0
Sum of the elements at column 2 is 13.0
Sum of the elements at column 3 is 13.0

*7.2

( Sum the major diagonal in a matrix ) Write a method that sums all the numbers in
the major diagonal in an

n * n matrix of integers using the following header:

public static double sumMajorDiagonal( double [][] m)

Write a test program that reads a 4-by-4 matrix and displays the sum of all its ele-
ments on the major diagonal. Here is a sample run: