假设文件中source.txtt只出现英文字母，统计该文件中字母aA出现的次数，并将结婚如以下形式写入calcCharNum.txt

怎么编程，谢谢大家，谢谢大家，谢谢大家，谢谢大家

public class Test {
    private void readAndCalc() {
        String parentFolder = "src/" + getClass().getPackageName().replace('.', '/');
        // 源文件路径
        String sourceFileName = parentFolder + "/source.txt";
        // 输出文件路径
        String outputFileName = parentFolder + "/calcCharNum.txt";

        File sourceFile = new File(sourceFileName);
        if (!sourceFile.exists()) {
            return;
        }
        FileInputStream fis = null;
        FileOutputStream fos = null;
        try {
            fis = new FileInputStream(sourceFile);
            // 读取数据缓存
            byte[] bytes = new byte[1024];
            // 字符出现次数计数
            int[] count = new int[52];
            int len;
            while ((len = fis.read(bytes)) != -1) {
                for (byte b : bytes) {
                    if (b >= 'A' && b <= 'Z') {
                        count[b - 'A']++;
                    }
                    if (b >= 'a' && b <= 'z') {
                        count[b - 'a' + 26]++;
                    }
                }
            }
            fis.close();
            fis = null;
            // 初始化要输出的文本
            StringBuilder stringBuilder = new StringBuilder();
            for (int i = 0; i < 26; i++) {
                stringBuilder.append((char) ('A' + i)).append(':').append(count[i])
                        .append("\t\t")
                        .append((char) ('a' + i)).append(':').append(count[i + 26])
                        .append("\n");
            }
            byte[] outBytes = stringBuilder.toString().getBytes(StandardCharsets.UTF_8);
            // 初始化输出文件
            File outputFile = new File(outputFileName);
            boolean handRst = outputFile.exists();
            if (handRst) {
                handRst = outputFile.delete();
            }
            if (!handRst) {
                handRst = outputFile.createNewFile();
            }
            if (handRst) {
                fos = new FileOutputStream(outputFile);
                fos.write(outBytes);
                fos.close();
                fos = null;
            }
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            try {
                if (fis != null) {
                    fis.close();
                }
                if (fos != null) {
                    fos.close();
                }
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }

    public static void main(String[] args) {
        Test test = new Test();
        test.readAndCalc();
    }
}

测试输出示例