JAVA-使用扫描仪读取字符

Question

Here is the problem that I'm working on.

We have to ask the user to enter a string, and then enter a character (any character would be fine). And then count the number of times that character appears in the scanner.

I cannot figure out how to add character to scanner. We haven't done arrays yet so I don't wanna go there but this is what I have done so far:

import java.util.Scanner;

public class Counter {

   public static void main (String args[]){

        String a;
        char b;
        int count;
        int i;


        Scanner s = new Scanner (System.in);


        System.out.println("Enter a string");

        a = s.nextLine();

        System.out.println("Enter a character");

        b = s.next().charAt(0);

        count = 0;
        for (i = 0; i <= a.length(); i++){

            if (b == s.next().charAt(b)){

                count += 1;

        System.out.println(" Number of times the character appears in the string is " + count);

                else if{

                    System.out.println("The character appears 0 times in this string");
            }


            }

        }

I know this is incorrect but I cannot figure this out right now.

Any help would be highly appreciated.

Answer 1

To verify your inputs [String, char] use a while loop for getting the character from the user. Basically you will check whether user enters a string of length 1 for character input. Here is the compiling and running version of your code:

import java.util.Scanner;

public class Counter
{
    public static void main ( String args[] )
    {
        String a = "", b = "";
        Scanner s = new Scanner( System.in );

        System.out.println( "Enter a string: " );
        a = s.nextLine();
        while ( b.length() != 1 )
        {
            System.out.println( "Enter a single character: " );
            b = s.next();
        }

        int counter = 0;
        for ( int i = 0; i < a.length(); i++ )
        {
            if ( b.equals(a.charAt( i ) +"") )
                counter++;
        }
        System.out.println( "Number of occurrences: " + counter );
    }
}

Answer 2

First, the for loop condition should be changed to :

for (i = 0; i < a.length(); i++)

The index starts from 0, but when you count length you start from 1. Therefore you don't need '='.

Second, in the for loop, you only need to do one thing: compare each character of a with b:

if (b == a.charAt(i))
    count += 1;

Here, compared with the other solution, char is cheaper than String to be compared.

Third, after the for loop, output depends on count:

if (count > 0)
    System.out.println(" Number of times the character appears in the string is "
                        + count);
else // must be count == 0
    System.out.println("The character appears 0 times in this string");