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

I'm pretty new with Java and it is my first time posting here and I'm trying to write a code that would let me check if the item (vehicle registration plate) inputted by the user is valid. The item has a format of: YYY-LL-SSSSSS, where

Starts with a three-digit year (i.e. YYY-LL-SSSSSS).
Continues with a dash i.e. ‘-‘
Followed by a two-letter county/city identifier (i.e. YYY-LL-SSSSSS). The possible county/city identifier (i.e. LL) are as follows: CK, CE, CN, CW, DN, DL, GY, KE, KK, KY, LK, LD, LH, LM, LS, MH, MN, MO, OY, RN, SO, TY, WD, WH, WX, WW
Continues with a dash i.e. ‘-‘
Ends with a one- to six-digit sequence number (i.e. YYY-LL-SSSSSS)

My code should be able to determine whether the plate number is valid by checking all the characters in the string, so if for example the user inputs '222-DN-1055' the plate 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:

My instantiable class

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<userInput.length();i  ){
            if (Character.isDigit(userInput.charAt(0))){
                strBuff.append(userInput.charAt(0));
            }
            else if (Character.isDigit(userInput.charAt(1))){
                strBuff.append(userInput.charAt(1));
                }
            else if (Character.isDigit(userInput.charAt(2))){
                strBuff.append(userInput.charAt(2));
                }
            else if (userInput.charAt(3)=='-'){
                strBuff.append(userInput.charAt(3));
                }
            else if (Character.isLetter(userInput.charAt(4))){
                strBuff.append(userInput.charAt(4));
                }
            else if (userInput.charAt(4) == 'c' || userInput.charAt(i) == 'd'|| userInput.charAt(i) == 'g' || userInput.charAt(i) == 'k' || userInput.charAt(i) == 'l' || userInput.charAt(i) == 'm'|| userInput.charAt(i) == 'o'|| userInput.charAt(i) == 'r' || userInput.charAt(i) == 's' || userInput.charAt(i) == 't' || userInput.charAt(i) == 'w'){
                strBuff.append(userInput.charAt(4));
                }
            else if (Character.isLetter(userInput.charAt(5))){
                strBuff.append(userInput.charAt(5));
                }
            else if (userInput.charAt(5) == 'k' || userInput.charAt(i) == 'e' || userInput.charAt(i) == 'n' || userInput.charAt(i) == 'w' || userInput.charAt(i) == 'l' || userInput.charAt(i) == 'y' || userInput.charAt(i) == 'd'|| userInput.charAt(i) == 'h' || userInput.charAt(i) == 'm' || userInput.charAt(i) == 's' || userInput.charAt(i) == 'o' || userInput.charAt(i) == 'x'){
                strBuff.append(userInput.charAt(5));
                }
            else if (userInput.charAt(6)=='-'){
                strBuff.append(userInput.charAt(6));
                }
            else if (Character.isDigit(userInput.charAt(7))){
                strBuff.append(userInput.charAt(7));
                }
            else if (Character.isDigit(userInput.charAt(8))){
                strBuff.append(userInput.charAt(8));
                }
            else if (Character.isDigit(userInput.charAt(9))){
                strBuff.append(userInput.charAt(9));
                }
            else if (Character.isDigit(userInput.charAt(10))){
                strBuff.append(userInput.charAt(10));
                }
            else if (Character.isDigit(userInput.charAt(11))){
                strBuff.append(userInput.charAt(11));
                }
            else if (Character.isDigit(userInput.charAt(12))){
                strBuff.append(userInput.charAt(12));
            }
            else{
                strBuff.append("Your registration plate is not valid.");
            }
            }

        validity=strBuff.toString();
    }

    //get
    public String getValidity(){
            return validity;
    }
}

My application class

import javax.swing.JOptionPane;
public class ItemCheckerApp{
    public static void main(String[] args){

        //vars
        String userInput;
        String validity;
        String response;

    do{//objects
        ItemChecker item;
        item=new ItemChecker();

        //input
        userInput=JOptionPane.showInputDialog(null,"Enter your vehicle registration plate (YYY-LL-SSSSSS): ").toUpperCase();

        //set
        item.setUserInput(userInput);

        //compute
        item.computeValidity();

        //get
        validity=item.getValidity();

        //output
        JOptionPane.showMessageDialog(null,"Your vehicle registration plate is: " validity);
        response=JOptionPane.showInputDialog(null,"Do you wish to check another plate? [Yes/No]?");
    }while(response.equalsIgnoreCase("yes"));
    }
}

The code doesn't really check if the plate is valid 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. Hope it makes sense what I'm trying to ask.

CodePudding user response：

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<userInput.length();i  ) {
            char c = userInput.charAt(i);
            if (i <= 2) {
                if (Character.isDigit(c)) {
                    //do whatever for true
                } else {
                    //return false etc
                }
            } else if (i == 3 || i == 6) {
                if (c == '-') {
                    //do whatever for true
                } else {
                    //return false etc
                }
            } else if (i <= 5) {
                //check for county identifiers
            } else {
                //finally check for digits
                if (Character.isDigit(c)) {

                } else {

                }
            }
        }
    }

CodePudding user response：

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.