How to prepare for unsuitable user inputs when using them to create an array in java

Question

I am trying to create a method that creates 2D array of unknown size and uses a loop to fill it with a character provided by the user in the main program. If the user gives eg negative values, the method should return null. I can get it to work, when the user uses suitable values, but not when the values are negative.

I use this:

public static char[][] createArr(int row, int col, char ch) {
char array[][] = new char[row][col];

if (row > 0 && col > 0) {
   for (int i = 0; i < col; i++) {
      for (int j = 0; j < row; j++) {
         array[j][i] = ch;
      }
   }
}
else {
   array = null;
}
return array;

I understand why it doesn't work, because

if (row > 0 && col > 0) {

comes AFTER I create the array, so the negative values create an error. But if I move it, then it gives the "cannot find symbol" error when I try to return the array to the main program.

How can I change this code so that it would not crash when the user inputs negative values?

PS. I am a student and we cannot use all java libraries, so I am asking how to get this type of code working without different helper classes.

Answer 1

I am trying to create a method that creates 2D array of unknown size and uses a loop to fill it with a character provided by the user in the main program. If the user gives eg negative values, the method should return null. I can get it to work, when the user uses suitable values, but not when the values are negative.

I use this:

public static char[][] createArr(int row, int col, char ch) {
char array[][] = new char[row][col];

if (row > 0 && col > 0) {
   for (int i = 0; i < col; i++) {
      for (int j = 0; j < row; j++) {
         array[j][i] = ch;
      }
   }
}
else {
   array = null;
}
return array;

I understand why it doesn't work, because

if (row > 0 && col > 0) {

comes AFTER I create the array, so the negative values create an error. But if I move it, then it gives the "cannot find symbol" error when I try to return the array to the main program.

How can I change this code so that it would not crash when the user inputs negative values?

PS. I am a student and we cannot use all java libraries, so I am asking how to get this type of code working without different helper classes.

Answer 2

I am trying to create a method that creates 2D array of unknown size and uses a loop to fill it with a character provided by the user in the main program. If the user gives eg negative values, the method should return null. I can get it to work, when the user uses suitable values, but not when the values are negative.

I use this:

public static char[][] createArr(int row, int col, char ch) {
char array[][] = new char[row][col];

if (row > 0 && col > 0) {
   for (int i = 0; i < col; i++) {
      for (int j = 0; j < row; j++) {
         array[j][i] = ch;
      }
   }
}
else {
   array = null;
}
return array;

I understand why it doesn't work, because

if (row > 0 && col > 0) {

comes AFTER I create the array, so the negative values create an error. But if I move it, then it gives the "cannot find symbol" error when I try to return the array to the main program.

How can I change this code so that it would not crash when the user inputs negative values?

PS. I am a student and we cannot use all java libraries, so I am asking how to get this type of code working without different helper classes.