Java Utililty Methods ConcurrentMap

readers.compute(fileNum, (key, value) -> {
    if (value == null)
        throw new IllegalMonitorStateException("file not locked: " + fileNum);
    if (value.longValue() == 1L) {
        return null;
    } else {
        return value - 1L;
});

readers.compute(fileNum, (key, value) -> value == null ? 1L : value + 1L);

if (clazz == null) {
    return null;
Logger logger = loggers.get(clazz);
if (logger == null) {
    logger = LoggerFactory.getLogger(clazz);
    loggers.put(clazz, logger);
return logger;

return MAP_OF_MAP.get(cacheName);

if (size.length == 0) {
    return new ConcurrentHashMap<K, V>();
} else {
    return new ConcurrentHashMap<K, V>(size[0]);

return (String) dataMap.get("__contextPath__");

Map<String, String> fs = mounts.get(id);
if (fs == null) {
    fs = new ConcurrentHashMap<String, String>();
    Map<String, String> prev = mounts.putIfAbsent(id, fs);
    if (prev != null) {
        fs = prev;
return fs;

Set<K2> inner = set.get(key);
if (inner == null) {
    inner = Collections.newSetFromMap(new ConcurrentHashMap<K2, Boolean>());
    Set<K2> old = set.putIfAbsent(key, inner);
    if (old != null)
        inner = old;
return inner;
...

Integer newFactor = null;
if (logFactorMap.containsKey(factorName)) {
    Integer oldFactor = logFactorMap.get(factorName);
    newFactor = oldFactor + 1;
    logFactorMap.put(factorName, newFactor);
} else {
    logFactorMap.put(factorName, 0);
    newFactor = 0;
...

T instance = null;
if (instanceMap.containsKey(classType)) {
    instance = (T) instanceMap.get(classType);
} else {
    instance = classType.newInstance();
    instanceMap.put(classType, instance);
return instance;
...