为什么我的代码不断抛出 StringIndexOutOfBoundsException？

Question

I have been trying to fix this for a while now and I just can't seem to get it. I'm trying to get the phone number from the user so I can display it but when I get all the users info the error occurs. Any help would be appreciated. Thank you.

Here is the code:

import java.util.Scanner;

public class Event 
{
    public static double pricePerGuestHigh = 35.00;
    public static double pricePerGuestLow = 32.00;
    public static final int LARGE_EVENT_MAX = 50;
    public String phone = "";
    public String eventNumber;
    private int guests;
    private double pricePerEvent;

    public void setPhone()
    {
        Scanner input = new Scanner(System.in);
        int count = 0;

        System.out.println("Enter your phone number: ");
        String phone = input.nextLine();
        int len = phone.length();
        for(int i=0; i<1; i++)
        {
            char c = phone.charAt(i);
            if(Character.isDigit(c))
            {
                count++;
                String ss = Character.toString(c);
                phone = phone.concat(ss);
            }
        }
        if(count != 10)
        {
            phone = "0000000000";
        }
    }

    public String getPhone()
    {
        // The error occurs in this method
        String ret = "(" + this.phone.charAt(0) + "" + this.phone.charAt(1)
        + "" + this.phone.charAt(2) + ")" + this.phone.charAt(3) 
        + "" + this.phone.charAt(4) + "" + this.phone.charAt(5)
        + "" + this.phone.charAt(6) + "" + this.phone.charAt(7)
        + "" + this.phone.charAt(8) + "" + this.phone.charAt(9);
        return ret;
    }

    public void setEventNumber()
    {
        Scanner input = new Scanner(System.in);
        System.out.println("Enter the event number: ");
        eventNumber = input.nextLine();
    }

    public void setGuests(int guests)
    {
        this.guests=guests;
        if(isLargeEvent())
            pricePerEvent = pricePerGuestHigh;
        else
            pricePerEvent = pricePerGuestLow;
    }

    public int getGuestsCount()
    {
        return guests;
    }

    public boolean isLargeEvent()
    {
        if(guests >= LARGE_EVENT_MAX)
        {
            return true;
        }
        else if(guests < LARGE_EVENT_MAX)
        {
            return false;
        }
        return isLargeEvent();
    }

    public String getEventNumber()
    {
        String ret1 = "Event Number: " + this.eventNumber;
        return ret1;
    }

    public int getGuests(boolean largeEvent)
    {
        return guests;
    }
}

The code where the error occurs has been marked with a comment.

Answer 1

The error means that you are trying to access the phone 's character at an index that does not exists .

Precisely, your phone field is never set inside your code so it's an empty String.

Anyway, you should also fix the for loop by using the len variable:

int len = phone.length();
for(int i = 0; i < len; i++)
{
    ...
}

By doing that, you cannot concern about StringIndexOutOfBoundsException because now the for automatically traverse only the chars present in the String .

Answer 2

The StringOutOfBoundsException is thrown whenever you're attempting to access a character in the string that doesn't exist at the given index .

From the code you've provided it seems as though you're accessing an empty string in the method getPhone() .

You can fix this by first checking if the string is empty with phone.isEmpty() .

public String getPhone() {

    if (phone == null || /*this.*/phone.isEmpty()) {
        // Handle the error accordingly.
        return null; // example
    }
    String ret = "(" + this.phone.charAt(0) + "" + this.phone.charAt(1)
    + "" + this.phone.charAt(2) + ")" + this.phone.charAt(3) 
    + "" + this.phone.charAt(4) + "" + this.phone.charAt(5)
    + "" + this.phone.charAt(6) + "" + this.phone.charAt(7)
    + "" + this.phone.charAt(8) + "" + this.phone.charAt(9);
    return ret;
}

While we're at it, I'd recommend not using string concatenation, as this will produce a large amount of overhead. Instead, use Java's string formatting .

This will not only increase the readability of your code, but it will (as mentioned before) reduce overhead, because strings in Java are immutable .

Answer 3

To make your code work you should make new local var (for example inputPhone ) and than change phone var of Event object. Also you should change condition in for loop.

public void setPhone()
{
    Scanner input = new Scanner(System.in);
    int count = 0;

    System.out.println("Enter your phone number: ");
    String inputPhone = input.nextLine();
    int len = inputPhone.length();
    for(int i=0; i<len; i++)
    {
        char c = inputPhone.charAt(i);
        if(Character.isDigit(c))
        {
            count++;
            String ss = Character.toString(c);
            phone = phone.concat(ss);
        }
    }
    if(count != 10)
    {
        phone = "0000000000";
    }
}