强化 Java 函数以提高其执行效率

// 缓存素数的列表
private static List<Integer> primes = new ArrayList<>();

public static boolean isPrime(int n) {
    if (primes.contains(n)) {
        return true;
    } else {
        // 添加到缓存中并检查素数
        boolean isPrime = isPrimeWithoutCache(n);
        if (isPrime) {
            primes.add(n);
        }
        return isPrime;
    }
}

// 重用 StringBuilder 避免字符串拼接
StringBuilder sb = new StringBuilder();
for (String s : words) {
    sb.append(s);
    sb.append(" ");
}

// 使用 HashMap 进行快速查找
Map<String, Integer> wordCount = new HashMap<>();
for (String word : words) {
    Integer count = wordCount.get(word);
    if (count == null) {
        count = 0;
    }
    wordCount.put(word, ++count);
}

// 并行计算素数
int[] numbers = {1, 2, 3, 4, 5, 6, 7, 8};
int numThreads = Runtime.getRuntime().availableProcessors();
ExecutorService executor = Executors.newFixedThreadPool(numThreads);

List<Callable<List<Integer>>> tasks = new ArrayList<>();
for (int start = 0; start < numbers.length; start += numThreads) {
    int end = Math.min(start + numThreads - 1, numbers.length - 1);
    tasks.add(() -> getPrimes(numbers, start, end));
}

List<Future<List<Integer>>> futures = executor.invokeAll(tasks);
List<Integer> allPrimes = new ArrayList<>();
for (Future<List<Integer>> future : futures) {
    allPrimes.addAll(future.get());
}

// 原始：
if (x != null && y != null) {
    return x + y;
} else {
    return 0;
}

// 简化后：
return (x != null && y != null) ? x + y : 0;