產生固定長度的字串

大家午安！我需要編寫一個產生固定長度字串的函數。其實乍看很簡單，就是這樣，但是我們希望這個功能能夠盡可能快速地實現。然後問題出現了──怎麼辦？實際上我構建了這段程式碼。迄今為止最快的方法是generateString，但我相信它可以加快速度。 public class StringGenerator{ private int strLength; private StringGenerator() { } public static StringGenerator getStringFixedLengthGenerator(int length){ StringGenerator stringGenerator = new StringGenerator(); stringGenerator.setStrLength(length); return stringGenerator; } public void setStrLength(int strLength) { this.strLength = strLength; } public String generateNextFixedString(){ return new String(); } public String generateThreadString() { ExecutorService executor = Executors.newSingleThreadExecutor(); Callable task = () -> { return generateString(strLength/2); }; Future future = executor.submit(task); Future future1 = executor.submit(task); String str = ""; try{ str = future1.get().concat(future.get()); }catch (Exception e){ } executor.shutdown(); return str; } public String generateString(){ return generateString(strLength); } public String generateString(int stringLength) { String characters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890"; Random rng = new Random(); char[] text = new char[stringLength]; for (int i = 0; i < stringLength; i++) { text[i] = characters.charAt(rng.nextInt(characters.length())); } return new String(text); } public String createRandomString() { String mCHAR = "ABCDEFGHIJKLMNOPQRSTUVWXYZ1234567890"; int STR_LENGTH = strLength; // длина генерируемой строки Random random = new Random(); StringBuilder builder = new StringBuilder(); for (int i = 0; i < STR_LENGTH; i++) { int number = random.nextInt(mCHAR.length()); char ch = mCHAR.charAt(number); builder.append(ch); } return builder.toString(); } }