TWO-DIMENSIONAL ARRAYS

DECLARING TWO-DIMENSIONAL ARRAY

Syntax   data type    arrayname[ ][ ];
Example
double  grades[ ] [ ];

CREATING TWO-DIMENSIONAL ARRAY

Syntax   data type    arrayname[ ][ ] ;
             arrayname = new data type [ROWS][COLS];
             where  ROWS - number of rows
                        COLS   - number of columns per row

Example
double  grades[ ] [ ];
grades  = new double [5][8];

You can combine the declaration and creation process into one step for arrays.

double grades[ ][ ] = new double [5][8];

INITIALIZING TWO-DIMENSIONAL ARRAY

Example   double grades [3][4] = { { 45.0, 89.0, 90.0, 67.0}, { 54.0, 75.0, 34.0, 99.0}, {88.0, 92.0, 10.0, 56.0} };

USING TWO-DIMENSIONAL ARRAY

• Use two for loops to process a two-dimensional array.
• Arrayname.length represents the number of rows.
• Arrayname[row number].length represents the number of columns.

Example
double grades [3][4] = { { 45.0, 89.0, 90.0, 67.0}, { 54.0, 75.0, 34.0, 99.0}, {88.0, 92.0, 10.0, 56.0} };
for (int row =0; row <grades.length; row++)
   for (int col = 0; col <grades[row].length; col++)
      { grades[row][col]  = grades[row][col] + 35.0;
       }

PASSING A TWO-DIMENSIONAL ARRAY TO A METHOD

• A single array element is passed to a method by value, the same as any primitive variable. Only a copy of the element is made, and the method does not alter the value of the element directly.
  Example
  public class Test
  { public static void main(String[ ] args)
    { double grades [3][4] = { { 45.0, 89.0, 90.0, 67.0}, { 54.0, 75.0, 34.0, 99.0}, {88.0, 92.0, 10.0, 56.0} };
       display(grades[2][1]);
     }
    public static void display(double d)
    { System.out.println (d);
     }
  }
• An entire array is passed to a method by reference, so the method may directly modify elements of the array.Because an array is an object, when the entire array is passed as a parameter, a copy of the reference to the original array is passed. The method can change an element of the array permanently because it is referring to the original element value.

        Example
        public class Test
       { public static void main(String[ ] args)
       { double grades [3][4] = { { 45.0, 89.0, 90.0, 67.0}, { 54.0, 75.0, 34.0, 99.0}, {88.0, 92.0, 10.0, 56.0} };
         display(grades);
       }
        public static void display(double g[3][4])
       {   for (int row =0; row <g.length; row++)
               { for (int col = 0; col <g[row].length; col++)
                    { System.out.println(g[row][col] + "   ");
                     }
                      System.out.println( );
                 }
       }
      }

RETURNING TWO-DIMENSIONAL ARRAY FROM THE METHOD

A method can return a two-dimensional array.

Syntax:  return  arrayname;

Example 
class Test
{ public double [ ] [ ] getGrades( )
  {double grades [3][4] = { { 45.0, 89.0, 90.0, 67.0}, { 54.0, 75.0, 34.0, 99.0}, {88.0, 92.0, 10.0, 56.0} };
    return grades;
  }
}

public class TestArray
{ public static void main(String[ ] args)
   { Test  x = new Test( );
      double  y[ ][ ]  = x.getGrades( );
    }
}