How to check if a correct character was entered by a user in a string in java?

Question

I'm trying to write a code that would let me check if the item inputted by the user is valid. The item has a format of: NNN-LL-NNNNNN, where N is a number and L is a letter.

My code should be able to determine whether the item is valid by checking all the characters in the string, so if for example the user inputs '222-DN-1055' it is valid but if it's '2-DN-1055' then it is not.

I can only use java methods I learnt in my course that's why I'm trying to do it with a String Buffer. I can't use regex.

Now, this is the code I have done so far:

public class ItemChecker{

    //vars
    private String userInput;
    private StringBuffer strBuff;
    private String validity;

    //constructor
    public ItemChecker(){
            strBuff=new StringBuffer();
    }

    //set
    public void setUserInput(String userInput){
            this.userInput=userInput;
    }

    //compute
    public void computeValidity(){
        for(int i=0;i


The code does not really work and I have no clue how to proceed from here. Also how do I make sure that if a user inputs more than six numbers at the end, the code would be considered invalid as well.

user_16034206 · Answer

here is a cleaned up version of your code, though its not complete. You can follow the style of the code to complete the rest of the logic.

public void computeValidity(){
        if (userInput.length() < 8 && userInput.length()> 13){
            //if length is not in between 8 to 13
            return; //exits function
        }
        for(int i=0;i

user_18736337 · Answer

I'd suggest that you can try to split the userInput. Solve the problem piece by piece.

I use Scanner for this example

    Scanner scan = new Scanner(System.in);
    String userInputPlate; 

    while (true) {
        userInputPlate = scan.nextLine();

        if (userInputPlate.equalsIgnoreCase("end")) {
            break;
        }

        // add the condition for 'SSSSSS'
        // i.e. > 8 
        // I omit it for readability
        if (userInputPlate.length() <= 13) {
            System.out.println("Please try again");
        }
    }
        String[] plateParts = userInputPlate.split("-");

        String YYY = plateParts[0];
        String LL = plateParts[1];
        String SSSSSS = plateParts[2];

        // notice I use "!" in if statement
        for (int i = 0; i < YYY.length(); i++){
            char[] YYYchar = YYY.toCharArray();
            if (!Character.isDigit((YYYchar[i]))){
                return;
            }
        }

        // for loop for LL, I skip it

        // do the same SSSSSS
        for (int i = 0; i < SSSSSS.length(); i++){
            char[] SSSSSSchar = SSSSSS.toCharArray();
                if(!Character.isDigit(SSSSSSchar[i])){
                    return;
                }
            }
        }

By doing so, you not only can debug with each segment easier, and it also improves the readability.

Hope this works for you.

How to check if a correct character was entered by a user in a string in java?

2 Answers