// Wrapper Class // Primitive Types // String and String Pool // Why is String immutable // Heap and Stack // Thread // - sleep() // - wait() // - notify() & notifyAll() (Interthread communication) // - join(); // - two types of creating Thread - extends Thread and using Runnable // - synchronized // - Atomic datatypes - AtomicLong,... // - volatile // PSVM // SOLID principle // Interface and Abstract Class and Concrete Class (Class) // Design pattern // - Creational - Singleton, Factory // - Behaviour - Command