for loop - looping more than its supposed to?

Question

public static void choice( String arrayString[], double arrayReal[])
{
    int choice;
    Scanner sc = new Scanner(System.in);
    System.out.println("1.display mark");
    System.out.println("2.exit");
    choice = sc.nextInt();



    while (choice !=2 && choice != 1)
    {
        System.out.println("invalid input enter again");
        choice = sc.nextInt();
    }

    switch (choice)
    {
            case 1:
                output(arrayString, arrayReal);
                break;
            case 2:
                System.out.println("exiting");
                break;
            default:
                System.out.println("invalid choice choose between 1 and 2");
                choice = sc.nextInt();
    }




}

public static void output(String arrayString[], double arrayReal[])
{
    String name;
    Scanner sc = new Scanner(System.in);
    for (int i=0;i<arrayString.length;i++)
    {
        System.out.println(arrayString[i]);
    }
    System.out.println("enter stident name");
    name = sc.nextLine();
    for (int k=0;k<arrayString.length;k++)
    {
        if(!arrayString.equals(name))
        {
            System.out.println("invalid name");
            choice(arrayString, arrayReal);
        }
    }

    for (int j=0;j<arrayString.length;j++)
    {
        if (arrayString[j].equals(name))
        {
            System.out.println("mark of " + arrayString[j] + "is " + arrayReal[j]);
        }
    }

im trying to validate the student name and if it doesnt equal to any of the names in the array return back to the menu. it does go back to the menu but the problem is after going back to the menu even if i type the correct student name if keps going back to the menu. i thought for loops were supposed to loop set amount of times and pass to the next code?? is that right? also is my approach correct? ive tried putting if else in the last for loop but that didnt end up as i wanted it to as well. any help is appreciated thanks!

EDIT- thanks for spotting the mistake. fixed !arrayString.equals(name) to !arrayString[k].equals(name) but still the same problem

Answer 1

The logic at this part, after adding the index, is still wrong:

for (int k=0;k<arrayString.length;k++)
{
    if(!arrayString[k].equals(name))
    {
        System.out.println("invalid name");
        ...
    }
}

this will print "invalid name" for every name in the list that is not the given name. Example: if the first name in the array does not match, you will get a message (and choice called), no matter if the second entry matches.

One way is to search the whole array until you find the name and then act on the result:

boolean found = false;
for (int k=0;k<arrayString.length;k++)
{
    if(arrayString[k].equals(name))
    {
        found = true;
        break;  // stop searching
    }
}

if (!found)
{
    System.out.println("invalid name");
    choice(arrayString, arrayReal);
}

Answer 2

Your problem ist here:

for (int k=0;k<arrayString.length;k++)
{
    if(!arrayString.equals(name))
    {
        System.out.println("invalid name");
        choice(arrayString, arrayReal);
    }
}

You are comparing an Array String[] arrayString with a String name. They are never going to be treated as equal and therefor your choice method is allways called. Also the whole loop is totally pointless as you never use your loop index k for anything.

You don't need a loop here at all. Instead you can simply convert the String array to a temporary list and check if it contains your input:

if(!Arrays.asList(arrayString).contains(name))
{
    System.out.println("invalid name");
    choice(arrayString, arrayReal);
}

Edit:

here a short main Method that can be used for testing:

public static void main(final String[] args) {
     final String[] test = { "Mark", "Peter" };
     final double[] test2 = { 1, 2 };
     choice(test, test2);
}

Input/Output:

OUTPUT: 1.display mark
OUTPUT:2.exit
INPUT: 1
OUTPUT: Mark
OUTPUT: Peter
OUTPUT: enter stident name
INPUT: Mark
OUTPUT: mark of Markis 1.0