You can still initialize arrays making use of lists, but this can be done for the entire array at once or for selected parts.

• Initializing completely making use of sets/lists should look like the following for two dimensional arrays.

dataType  arrayName[ ][ ] = {{list for row 0}, {list for row 1}, . . . {list for row n-1}}

where {list for row i} = {e₀, e₁, e₂, ... e_i} of the appropriate data type.  Thus, rows can each have a different number of elements.

• In order to develop the contents of each row separately the developer is likely to have to do something like the following.

dataType  arrayName[ ][ ];

arrayName = new dataType[numberRows][ ];

arrayName[rowNumber][ ] = {e₀, e₁, e₂, ... e_i};

Then the developer can add the appropriate commands for initializing each row.

• Something analogous to this can also be used to prepare a multidimensional array for initializing either within loops or from a GUI.

Now we will develop and discuss an example to illustrate these options.  You should call the following applet InitMultiDimArray.java.

JTextArea outputArea;

public void init( )
{

outputArea = new JTextArea( );
Container c = getContentPane( );
c.add(outputArea);

int array1 [][] = {{1,2,3},{4,5,6}};
int array2 [][] = {{1,2},{3},{4,5,6}};
int array3 [][];
array3 = new int [3][]; // array3 has 3 rows
array3[0] = new int[5]; // the first row has 5 columns
array3[1] = new int[2]; // the second row has 2 columns
array3[2] = new int[7]; // the third row has 7 columns

// actually initializing the values in array3
for (int i = 0; i < array3.length; i++)

for (int j = 0; j < array3[i].length; j++)

array3[i][j] = (i+1)*(j+1);

outputArea.setText("Values in array1 by row are\n");
buildOutput(array1);

outputArea.append("Values in array2 by row are\n");
buildOutput(array2);

outputArea.append("Values in array3 by row are\n");
outputArea.append("array3[ i ][ j ] = (i+1)(j+1)\n");
buildOutput(array3);

}

public void buildOutput(int a[][])
{

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

for (int j = 0; j < a[i].length; j++)

// display each element of the array
// while putting a space in between them
outputArea.append(a[i][j] + " ");

// add a new line for each new row
outputArea.append("\n");

}

outputArea.append("\n");

}

}

• The imports bring in the necessary extra packages and classes
  • import java.awt.Container
    • for the container used for output
  • import javax.swing.*
    • for the swing classes and the JApplet in particular
• Declare and define the overall inclusive class InitMultiDimArray
  • extends JApplet
• Declare and define the init( ) method
  • instantiate a JTextArea called outputArea for output
  • instantiate a container called c for output
  • add the JTextArea to the container c
  • declare and initialize a new two dimensional integer array1 with a list
    • rows are each the same size
  • declare and initialize a new two dimensional integer array2 with a list
    • rows each have different size
  • declare a new two dimensional integer array3
  • declare the number of rows in array3
  • declare the number of columns in each of thee rows
  • use a for loop to go through the rows of array3
    • notice the use of array3.length to determine the number of loops based on  the number of rows
    • use a nested for loop to go through every column in each of these rows
      • notice the use of array3[row].length to determine the number of loops based on  the number of columns in each row
        • assign (i + 1)(j + 1) to the array3[ i ][ j ] element
  • append a descriptive phrase to the outputArea before displaying array1
  • use a user developed method called buildOutput(array1)
    • passing array1 to display array1 in the outputArea
  • append a descriptive phrase to the outputArea before displaying array2
  • use a user developed method called buildOutput(array2)
    • passing array1 to display array2 in the outputArea
  • append two descriptive phrases to the outputArea before displaying array3
  • use a user developed method called buildOutput(array3)
    • passing array1 to display array3 in the outputArea

     

 

• declare and define the user defined method buildOuput( )
  • requires the array a[ ][ ] to be passed
  • returns nothing
  • use a for loop to go through the rows of a
    • notice the use of a.length to determine the number of loops based on  the number of rows in whatever is passed to the method
    • use a nested for loop to go through every column in each of these rows
      • notice the use of a[row].length to determine the number of loops based on  the number of columns in each row
        • append the a[ i ][ j ] element and a blank for each element in the row
        • append a newline character each time the row tracking loop goes to a new row
  • append a newline character just before completing append for output display for each time the method is invoked.

That's it!