java - 如何检查用户是否在java中的字符串中输入了正确的字符？

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<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;
    }
}

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.

Answer 1

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 {

                }
            }
        }
    }

Answer 2

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.