Core Java Interview Questions

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Core Java interview questions with answers

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What is an abstract class? | Explain the difference between abstract class and interfaces. Answer: An abstract class defines an abstract concept which can’t be..... What is an interface? Answer: An interface is a set of method definition without implementation. It is a protocol.... Explain JVM (Java virtual machine) and JIT (Just in compilation). Answer: JVM is a virtual computer that runs the compiled java program. JVM is software..... Explain how to implement polymorphism in JAVA. Answer: Capacity of a method to do different things based on the object that...... Core Java Interview questions with answers posted on August 11, 2008, 19:00 pm by Amit Satpute What are Native methods in Java? Answer: Java applications can call code written in C, C++, or assembler. This is sometimes done......... What are class loaders? Answer: The class loader describes the behavior of converting a named class into the bits responsible...... What is Reflection API in Java? Answer: The Reflection API allows Java code to examine classes and objects at run time..... Explain the difference between static and dynamic class loading. Answer: The static class loading is done through the new operator...... Explain Shallow and deep cloning. Answer: Cloning of objects can be very useful if you use the prototype pattern or if you want to store an internal copy...... What is the purpose of Comparator Interface? Answer: Comparators can be used to control the order of certain data structures and collection of objets too...... Explain the impact of private constructor. Answer: Private Constructors can't be access from any derived classes neither from another class...... What are static Initializers? Answer: A static initializer block resembles a method with no name, no arguments, and no return type...... Explain autoboxing and unboxing. Answer: To add any primitive to a collection, you need to explicitly box (or cast) it into an appropriate wrapper class..... What is Map and SortedMap interface? Answer: Maps are used to store the key-Value pairs..... Define the purpose of Externalizable Interface. Answer: The Externizable interface extends the serializable interface...... What is transient and volatile modifiers? Answer: When serializable interface is declared, the compiler knows that the object has to be handled.......... What are daemon threads? Answer: Threads that work in the background to support the runtime environment are called daemon threads..... What is JAVAdoc utility? Answer: Javadoc utility enables you to keep the code and the documentation in sync easily...... Explain the difference between StringBuilder and StringBuffer class. Answer: StringBuilder is unsynchronized whereas StringBuffer is synchronized..... Explain semaphore and monitors in java threading. Answer: A semaphore is a flag variable used to check whether a resource is currently being used by another thread or process..... What are Checked and UnChecked Exception? Answer: The java.lang.Throwable class has two subclasses Error and Exception. There are two types..... What are different types of inner classes? Answer: Local classes - Local classes are like local variables, specific to a block of code......... Why do we need wrapper classes? Answer: Wrapper classes are used to be able to use the primitive datatypes as objects........ What is the difference between error and an exception? Answer: Errors are abnormal conditions that should never occur. Not to be confused with the compile time errors..... What is the difference between preemptive scheduling and time slicing? Answer: Under time slicing, a task executes for a predefined slice of time and then reenters the pool of...... What is serializable Interface? Answer: If we want to transfer data over a network then it needs to be serialized. Objects cannot be transferred........ How does thread synchronization occurs inside a monitor? Answer: A Monitor defines a lock and condition variables for managing concurrent access to shared data....... What is the difference between AWT and Swing? Answer: Classes in swing are not OS dependent. They don’t create peer components,.......... What is meant by Stream Tokenizer? Answer: The StreamTokenizer class takes an input stream and parses it into "tokens", allowing.......... What is meant by getCodeBase and getDocumentBase method? Answer: The getCodebase() method is also commonly used to establish a path to other files............