Touchpad Touchpad - 6 months ago 24
Java Question

Java 2d Array unable to edit value and properly return element back null values

My knowledge with java language is very new. Most of my knowledge are from googling up on how to do things. I've been working on a console program in java that uses a switch statement. The entire program utilizes an String [20][5] array. I've written the code to now be able to add entry, save array to file, load entries from file into the array.

The problems now is edit and removing entries. I am able to return values to null but it'll look like this [[null], [null, null, null, null, null].

I want the value to return to [null, null, null, null, null], [null, null, null, null, null].

The Edit entry some reasons return an java.lang.ArrayIndexOutOfBoundsException:1 .

Could someone point out my error? Also the Array is globally declare.

public static String[][] rem(){
Scanner input = new Scanner(System.in);
int x,y=0;
//for(int i=0;i<array.length;i++){
//if(array[i][0]!=null){
System.out.println(Arrays.deepToString(array));//}
//}
System.out.println("Which entry would you like to remove? "
+ "\n" + "Enter number 0 - 20");
x = input.nextInt();
array[x][y]=null;
return array;}


public static String[][] edit(){
Scanner input = new Scanner(System.in);
String k;
int j;
int g;
// for(int i=0;i<array.length;i++){
//if(array[i][0]!=null){
//System.out.println(Arrays.deepToString(array));}
//}
System.out.println("Which entry would you like to edit? "
+ "\n" + "Enter number 0 - 20");
j = input.nextInt();
System.out.println("What would you like to edit? "
+"\n" + "Enter number 0 - 5");
g = input.nextInt();
System.out.println("You are now editing.");
k = input.next();
array[j][g] = k;
return array;}


Update

I think I figure my issue. The array properly edit values I manually input. It's when I load data into the array that causes problem because when it loads data it loads as String []. I need a code that will load the data as String[][] or as array of arrays.

public static String[][] load()throws FileNotFoundException, IOException{
menu();
copyFile();
String file = ("c:/temp/Address.txt");
Scanner scan = new Scanner(new FileReader(file));
// initialises the scanner to read the file file

//String[][] entries = new String[100][3];
// creates a 2d array with 100 rows and 3 columns.
//int i = 0;
while(scan.hasNextLine()){
array[i][i] = scan.next().split("," , "\t");
i++;
}
//loops through the file and splits on a tab

//for (int row = 0; row < array.length; row++) {
// for (int col = 0; col < array[0].length; col++) {
// if(array[row][col] != null){
// System.out.print(array[row][0] );
// }
// }
// if(array[row][0] != null){
// System.out.print("\n");
//}
// }
//prints the contents of the array that are not "null"
selectMenu();
return array;}


Update 2

I have found the solution to solving the loading data issue. The solution is simple! I'll leave the code here for reference. Though, all of the codes could use some beautifying.

public static String[][] load()throws FileNotFoundException, IOException{
menu();
copyFile();
String file = ("c:/temp/Address.txt");
Scanner scan = new Scanner(new FileReader(file));
FileReader fr = new FileReader("c:/temp/Address.txt");
BufferedReader br = new BufferedReader(fr);

//int j=0;
//int lineNo = 0;
//String line = br.readLine();
//while(line!=null)
//{
//for(int i = 0; i < 5; i++)
//{
//array[lineNo][i] = line.substring(i,4);
//}
// lineNo++;
//line = br.readLine(); // This is what was missing!
//}
//while(scan.hasNextLine()){
//while(scan.hasNext()){
//for(j=0;j<5;j++){
for(int i = 0; i < 20; ++i){
for(int j = 0; j < 5; ++j)
{
if(scan.hasNext())
{
array[i][j] = scan.next();
//i++;
//j++;
}
//i++;
}
}

selectMenu();
return array;}


Update 3

So after figuring out on how to use the delimiter it sorts of give me a weird issue. It adds return at the end of the column. [null, null, null, null, null return]. I used ",|\n" as my delimiter. Is there a better method? Update: Added a .trim(); solve the final issue with load. Now it's perfected in its current job. Though, I'm sure there might be less primitive methods.

public static String[][] load()throws FileNotFoundException, IOException{
copyFile();
//delimiter removes the comma or return to the next line. "\n" new line
Scanner scan = new Scanner(new FileReader(file)).useDelimiter(",|\n");
for(int i = 0; i < 20; ++i){
for(int j = 0; j < 5; ++j){
if(scan.hasNext())
array[i][j] = scan.next().replace(",", "").trim();
}
}
System.out.println("File loaded successfully!!");
scan.close();
return array;}

Answer

This is an off by one error, very subtle mistake:

Although you have 20 rows and 5 columns, arrays use a 0 based index(start counting from 0 instead of 1). Use your fingers to count from 0 - 5 and you will see that there are actually 6 numbers instead of 5 which is causing your OutOfBoundsException as you don't have a 6th element. Therefore to access your rows and columns, the range should be between: 0 - 19 (for the columns) and 0 - 4 (for the rows)

Or

1 - 20 (for the columns) and 1 - 5 (for the rows) and then subtract 1 from your scanners input since remember arrays use 0 based index.

update for the file reading:

public static String[][] load() {

   try{
      FileReader fr = new FileReader("c:/temp/Address.txt");
      BufferedReader bf = new BufferedReader(fr);
      String presentLine = "";
      for(int i = 0; i < 20; i++) {
        for(int j = 0; i < 5; j++) {
             if ((presentLine = bf.readLine()) != null) {
                   array[i][j] = presentLine;
             }
        }
      }
   } catch(Exception e) {
      System.out.println(e);
   }

   selectMenu();
   return array;
}

Although this could be made way better but it's okay. You could store 20 and 5 as static variables called rows and columns respectively to avoid using hard coded numbers.

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