Java loop not working because of wrong scanner usage

Java loop not working because of wrong scanner usage

Problem Description:

I’m making a text editor in java.
I’m using a switch to create a menu.
One of the options of the menu is to insert lines to the existing array where i need to make a loop to add strings to an array and make it stop when i add a empty string.
Note: i cannot use array lists.
i can only use this array.

int tamMax=100;
String [] linhas = new String[tamMax];

This is the code i have so far

        System.out.println("(I)nserir linhas no fim (termine com uma linha vazia");
        System.out.println("(L)istar linhas");
        System.out.println("(A)pagar última linha");
        System.out.println("(E)ditar");
        System.out.println("(F)erramentas");
        System.out.println("(S)air");
        menuPrincipal = input.next().charAt(0);
        switch(menuPrincipal) {
            case 'i':
            case 'I':
                int i=0;
                while (true) {  
                    linhas[i] = input.nextLine();
                    System.out.println(linhas[i]);
                    if (linhas[i].isEmpty()) {
                        break;
                    }
                    i++;
                }
                System.out.print(Arrays.toString(linhas));

The loop itself is working fine, the problem is when i put the loop inside the switch case, once i do that and i press "i" the loop stops working, it doesn’t let me type anything and only outputs the following result:[, null, null, null, null, null, null, null …

Solution – 1

linhas[i] will always be null. You want to check the string that was inserted in the previous iteration (i - 1).

You can do the check within the for-loop body.

for (int i = 0; ; i++) {
    linhas[i] = input.nextLine();
    System.out.println(linhas[i]);
    
    if (linhas[i].isEmpty()) {
        break;
    }
}

If you don’t want the empty string to be inserted, move the check before assignment.

String element = input.nextLine();
System.out.println(element);
if (element.isEmpty()) {
    break;
}
linhas[i] = element;
i++;

Since you do not know the number of times the loop will run, a while loop may be preferred.

while (true) {
    linhas[i] = input.nextLine();
    System.out.println(linhas[i]);
    if (linhas[i].isEmpty()) {
        break;
    }
    i++;
}