RentrantLock is almost the same as synchronized keyword. Only difference is that synchrnozied keyword needs a block. It maintains a queue for the threads. RentrantLock lock = new ReentrantLock(); lock.lock(); try { do something.. } finally { lock.release(); } ReentrantReadWriteLock. It also maintains a queue for threads. When it has queue: [readThread1, readThread2, writeThread3, readThread4]… Read More »
nohup, means “no hangup”. Means even logout, let it run. &, run in background. For instance: nohup java -jar abc.jar &
logger(threshold=INFO) -> appender(threshold=WARN) https://youtu.be/V-kHwLeGsC4?t=580
wait(), notify(). obj.wait() will release the object’s lock, until some other thread calls obj.notify(). When calling obj.wait(), current thread should own obj. Normally, it is called like: synchronized(obj) { // acquire obj obj.wait(); } IllegalMonitorStateException will be thrown if current thread doesn’t own obj. obj.notify() wakes up single thread which waits for obj lock. obj.notifyAll()… Read More »
Guava: Preconditions.checkNotNull Guava: Preconditions.checkArgument JDK: Objects.requireNotNon NullPointerException or IllegalArgumentException 1. Many APIs in the JDK pro-actively throws NullPointerException. This suggests that throwing NPE is a Java convention. 2. Effective Java Item 60: “Arguably, all erroneous method invocations boil down to an illegal argument or illegal state, but other exceptions are standardly used for certain kinds… Read More »
default can be used in switch statement. default can be used in annotation, specifying the default value. For example: @Target(ElementType.METHOD) @Retention(RetentionPolicy.RUNTIME) @interface Todo { String author() default “Yash”; } @Todo(author = “Yashwant”) public void incompleteMethod1() { //Some business logic is written //But it’s not complete yet }
public static void converterTest() { BiMap<Integer, String> biMap = HashBiMap.create(); biMap.put(1, “a”); biMap.put(2, “b”); biMap.put(3, “c”); Converter<Integer, String> converter = Maps.asConverter(biMap); System.out.println(converter.convert(1)); System.out.println(converter.reverse().convert(“b”)); }
Optional can avoid null of an Object. public static void nullable() { Optional<Integer> i = Optional.fromNullable(null); System.out.println(i.or(2)); // output 2, because is null System.out.println(i.get()); // IllegalStateException } public static void absent() { Optional<Integer> i = Optional.absent(); System.out.println(i.or(2)); // output 2, because value is absent System.out.println(i.get()); // IllegalStateException } public static void of() { Optional<Integer> i… Read More »
Below one is the nice cache scheme. Just to remind that LoadingCache is an abstract class, not a interface. So it can’t be wrote in lambda expression. public static void cacheBuilderCase() throws Exception { LoadingCache<Integer, String> memo = CacheBuilder.newBuilder().build( new CacheLoader<Integer, String>() { public String load(Integer key) throws Exception { return String.valueOf(key); } }); System.out.println(memo.get(1));… Read More »