如何使用switch循环计算字符串中的多个字符出现次数？ Java的

Question

Looking to count the letters a, e, s, t also the upper case. Using the switch loop. I have already have it so it counts the blank spaces but I dont know how to setup the switch and how to print it. Thank you

import java.util.Scanner;

public class Count {
    public static void main(String[] args) {
        String phrase;   // a string of characters
        int countBlank;  // the number of blanks (spaces) in the phrase
        int length;      // the length of the phrase
        char ch;         // an individual character in the string

        Scanner scan = new Scanner(System.in);
        // Print a program header
        System.out.println();
        System.out.println("Character Counter");
        System.out.println();
        // Read in a string and find its length
        System.out.print("Enter a sentence or phrase: ");
        phrase = scan.nextLine();
        length = phrase.length();
        // Initialize counts
        countBlank = 0;
        // a for loop to go through the string character by character
        // and count the blank spaces
        // Print the results System.out.println ();
        for (int i = 0; i < phrase.length(); i++) {
            if (Character.isWhitespace(phrase.charAt(i))) {
                countBlank++;
            }
        }
        ch = phrase.charAt(phrase.length());

        System.out.println();

        System.out.println("Number of blank spaces: " + countBlank);

        System.out.println();
    }
}

Answer 1

I think this might be helpful,

import java.util.Scanner;
class Count {
    public static void main(String[] args) {
        String phrase;   // a string of characters
        int countBlank;  // the number of blanks (spaces) in the phrase
        int length;      // the length of the phrase
        char ch;         // an individual character in the string


        phrase = "abcd efgh skjadh sjds";
        length = phrase.length();
        int i = 0;
        // Initialize counts
        countBlank = 0;
        // a for loop to go through the string character by character
        // and count the blank spaces
        // Print the results System.out.println ();
        int aCount = 0;
        int eCount = 0;
        int sCount = 0;
        int tCount = 0;
        int capACount = 0;
        int capECount = 0;
        int capSCount = 0;
        int capTCount = 0;
        while(i < length) {
            ch = phrase.charAt(i);
            switch(ch) {
                case 'a' :
                    aCount++;
                    break;
                case 'e' : 
                    eCount++;
                    break;
                case 's' :
                    sCount++;
                    break;
                case 't' : 
                    tCount++;
                    break;
                case 'A' :
                    capACount++;
                    break;
                case 'E' :
                    capECount++;
                    break;
                case 'S' :
                    capSCount++;
                    break;
                case 'T' :
                    capTCount++;
                    break;

            }
            i++;
        }

        System.out.println("Number of a: " + aCount);
        System.out.println("Number of e: " + eCount);
        System.out.println("Number of s: " + sCount);
        System.out.println("Number of t: " + tCount);
        System.out.println("Number of A: " + capACount);
        System.out.println("Number of E: " + capECount);
        System.out.println("Number of S: " + capSCount);
        System.out.println("Number of T: " + capTCount);

    }
}

Answer 2

How about using the JDK instead:

int countBlank = phrase.length() - phrase.replace(" ", "").length();
int countAest = phrase.length() - phrase.replaceAll("(?i)[aest]", "").length();

These two lines work by removing the characters of interest then using the change in length to give you the count.

FYI, in regex, (?i) means "ignore case", and [aest] means "any of the characters a, e, s or t".

Answer 3

Consider putting the characters you want to find in a String also. This way you can use the charAt() method on the input phrase as well as the string of characters you want to find.

    public static void main(String[] args) {
        // Print a program header
        System.out.println();
        System.out.println("Character Counter");
        System.out.println();

        // Read in a string and find its length
        System.out.print("Enter a sentence or phrase: ");
        Scanner scan = new Scanner(System.in);
        String phrase = scan.nextLine();
        int length = phrase.length();

        // Initialize counts
        String findChars = " AaEeSsTt"; // we will count each of these characters
        int[] counts = new int[findChars.length()]; // the counts of findChars

        // Go through the string character by character and count findChars
        for (int i = 0; i < length; i++) {
            char ch = phrase.charAt(i);
            for (int n = 0; n < findChars.length(); n++) {
                char find = findChars.charAt(n);
                if (ch == find) {
                    counts[n]++;
                    break;
                }
            }
        }
        System.out.println();

        // Print the results to System.out
        for (int n = 0; n < findChars.length(); n++) {
            System.out.println("Number of '"
                + findChars.charAt(n) + "': " + counts[n]);
        }
        System.out.println();
    }

Answer 4

In the example below, first we taking one sentence as String , which we will read Character by Character , and as we read each Character we will increment (respective index value), for int Array , like:

int value = ( int ) sentence.charAt (i);
characterCount [value]++;

If only you knew, that you reading ASCII character set, then you can use this approach too, or modify it to suit the needs of the project.

public class AlphabetCountingExample {

    private static final int TOTAL_ASCII_CHARACTERS = 256;
    private String sentence;
    private int [] characterCount;

    public AlphabetCountingExample () {
        characterCount = new int [TOTAL_ASCII_CHARACTERS];
        sentence = "Hello there!!!";
    }

    private void performTask () {
        countCharacters ();     
        displayCount ();
    }

    private void countCharacters () {
        for ( int i = 0; i < sentence.length (); ++i ) {
            int value = ( int ) sentence.charAt (i);
            characterCount [value]++;
        }
    }

    private void displayCount () {
        for ( int i = 0; i < characterCount.length; ++i ) {
            if ( characterCount [ i ] > 0 ) {
                System.out.println ( "Character: " + (char) i +
                                " Count: " + characterCount [ i ] );
            }
        }
    }

    public static void main (String[] args) {
        new AlphabetCountingExample ().performTask ();
    }
}