Core Java - Level III

Practice 54 Core Java - Level III interview questions with detailed answers. Part of the Core Java track on Java Interview Hub.

• Describe a scenario where you used a PriorityQueue, and explain why it was chosen over other types of queues.
• What are enums in Java and how are they useful?
• What is the Builder Pattern in Java? How is it different from the Factory Pattern?
• What is the impact of declaring a method as final on inheritance?
• Can method overloading be determined at runtime?
• How does Java resolve a call to an overloaded method?
• What is the diamond operator, and how does it work?
• Explain inner classes in Java.
• Can inner classes have static declarations?
• What is the significance of an anonymous inner class?
• What do you think Java uses: pass by value or pass by reference?
• What are the differences between implementing Runnable and extending Thread in Java?
• What is a marker interface?
• Can you provide a scenario where creating a custom marker interface would be beneficial?
• How does Java determine which method to call in the case of method overloading?
• What happens if two packages have the same class name?
• How do you access a package-private class from another package?
• Can you modify a final object reference in Java?
• What is the default access modifier if none is specified?
• What are the potential issues with using mutable objects as keys in a HashMap?
• What would happen if you override only the equals() method and not hashCode() in a custom key class used in HashMap?
• What is the difference between HashMap and IdentityHashMap in terms of how they handle keys?
• How does Collections.sort() work internally?
• What would happen if you try to sort a list containing null elements using Collections.sort()?
• Can you sort a list of custom objects using Collections.sort() without providing a Comparator?
• What is the difference between using Collections.sort() and Stream.sorted() in Java 8+?
• Can an enum extend another class in Java?
• How do you iterate over all values of an enum?
• Can you serialize static fields in Java?
• What happens if an exception is thrown during the serialization process?
• What is the difference between synchronized collections and concurrent collections in Java?
• How does ConcurrentHashMap achieve thread safety without locking the entire map?
• What is a race condition and how can it be prevented in Java?
• What is a deadlock in Java and how can you avoid it?
• What is the difference between wait() and sleep() methods?
• What is the difference between Callable and Runnable?
• What is Future in Java?
• What is CompletableFuture in Java?
• What is ForkJoinPool in Java?
• What is the difference between process and thread?
• What is ThreadLocal in Java?
• What is the Executor Framework in Java?
• What is a thread pool and why is it used?
• What is the difference between fixed thread pool and cached thread pool?
• What is starvation in Java multithreading?
• What is livelock in Java?
• How does TreeSet sort elements when it stores objects and not wrapper classes?
• Suppose you have multiple interfaces with default methods that a class implements. How would you resolve method conflicts?
• How do JVM optimizations affect the performance of Java applications?
• Can ‘this’ be used in a static method or block?
• Explain Java Class Loader.
• Is it possible to unload a class in Java?
• How does class loading affect memory usage?
• What is the role of ExecutorService in the Executor Framework? What methods does it provide?