统计字符串-课程设计

7. 字符数统计(满分50分) 版本1：满分15分 Write a method that counts the number of letters in a string using the following header: public static int countLetters (String s) Write a test program that prompts the user to enter a string and displays the number of occurrences of letters in the string. 版本2：满分20分 Write a class that displays the number of occurrences of each letter in a string using histogram. The class header should be: public class Histogram extends JPanel { … } Write a test program that prompts the user to enter a string and displays a histogram of the number of occurrences of each letter in the string using Histogram class. The display is as shown as following figure: 版本3：满分20分 Write a program that prompts the user to enter the name of an ASCII text file and display the frequency of the letters in the file using following design: public class ShowFrequency { public static void main(String[] args) throws Exception { …. BufferedInputStream fileInput = new BufferedInputStream( new FileInputStream(new File(filename))); …. } }