double[][] multi = new double[][] {
  { 10, 20, 30, 40, 50 },
  { 1.1, 2.2, 3.3, 4.4 },
  { 1.2, 3.2 },
  { 1, 2, 3, 4, 5, 6, 7, 8, 9 }
};

// Get the maximum number of columns among all rows.
int maximumColumns = 0;
for (double[] row : multi) {
    if (row.length > maximumColumns) {
        maximumColumns = row.length;
    }
}

for (int column = 0; column < maximumColumns ; column++) {
    for (int row = 0; row < multi.length; row++) {
        if (column >= multi[row].length) {
            // There is no value for this column.
        } else {
            // Do stuff here with multi[row][column].
        }
    }
}

int columnToIterate = // Your column.
for (int row = 0; row < multi.length; row++) {
    if (columnToIterate < multi[row].length) {
        // Do stuff here with multi[row][columnToIterate].
    }
}

for (double[] row: multi) {
       for(double value: row) {
       }
   }

for(int i=0; i<multi.length; i++) {
            for(int j=0; j<multi[i].length; j++) {
                System.out.println("Values at multi["+i+"]["+j+"] is "+multi[i][j]);
            }
        }