Core Java - Level II

Practice 191 Core Java - Level II interview questions with detailed answers. Part of the Core Java track on Java Interview Hub.

• Can you tell me the difference between JVM, JRE, and JDK?
• What are the key components of JVM Architecture?
• Can a Java application be run without installing the JRE?
• Is it possible to have the JDK installed without having the JRE?
• What are Memory storages available with JVM?
• Which is faster to access between heap and stack, and why?
• How does garbage collection work in Java?
• What's the role of finalized() method in garbage collection?
• Can you tell me what algorithm JVM uses for garbage collection?
• How can memory leaks occur in Java even we have automatic garbage collection?
• Is Java 100% object oriented programming language?
• What are the advantages of Java being partially object-oriented?
• What is the use of object-oriented programming languages in the enterprise projects?
• Explain public static void main(String args[])?
• What will happen if we don't declare the main as static?
• Can we override the main method?
• Can we overload the main method?
• Can JVM execute our overloaded main method?
• What's the difference between primitive data types and non primitive data types?
• Can primitive data types be NULL?
• Can we declare pointer in java?
• What are wrapper classes?
• Why do we need wrapper classes?
• Why we use wrapper class in collections?
• Can you explain the difference between unboxing and autoboxing in Java?
• Can you provide an example where autoboxing could lead to unexpected behavior?
• Is there a scenario where autoboxing and unboxing could cause a NullPointerException?
• Can you explain the role of each try, catch, and finally block in exception handling?
• What happens if a return statement is executed inside the try or catch block? Does the finally block still execute?
• Is it possible to execute a program without a catch block? If so, how would you use try and finally together?
• How does exception handling with try-catch-finally affect the performance of a Java application?
• Can you tell me a condition where the finally block will not be executed?
• Can we write multiple finally blocks in Java?
• What is the exception and the differences between checked and unchecked exceptions?
• How would you handle multiple exceptions in a single catch block?
• What is the difference between a Throwable and an Exception in Java?
• Discuss the difference between finalize() and finally. Under what circumstances might finalize() not get called in a Java application?
• What is string pool?
• Are there any scenarios where using the string pool might not be beneficial?
• Can you please tell me about String and StringBuffer?
• How does StringBuilder differ from StringBuffer, and when should each be used?
• Give a scenario where StringBuffer is better than the String?
• What is the difference between a String literal and a String object?
• Why is String immutable?
• What are the packages in Java?
• Why packages are used?
• What are access modifiers in Java?
• Can you provide examples of when to use each type of access modifier?
• Why do we use getters setter when we can make fields public and setting getting directly?
• Can a top-level class be private or protected in Java?
• Explain the concepts of classes and objects in Java.
• What are the ways to create an object?
• Can a class in Java be without any methods or fields?
• What are the methods available in the Object class, and how are they used?
• What are anonymous classes and their advantages?
• What is Singleton Class?
• How can we create this singleton class?
• Are these threads safe?
• What is a constructor in Java?
• Can we use a private constructor?
• Can constructor be overloaded?
• What is immutability mean in Java?
• Why immutable objects are useful for concurrent programming?
• What are immutable classes?
• How can we create immutable class?
• What does Java's inheritance mean?
• Can a class extend its own?
• Why multiple inheritance is not possible in java?
• What is the difference between inheritance and composition?
• Discuss the principle of "composition over inheritance". Provide an example where this principle should be applied in Java application design.
• What is the difference between association, aggregation, and composition in Java?
• Explain the IS-A (inheritance) and Has-A (composition) relationships in Java.
• What does mean by polymorphism in Java?
• How does method overloading relate to polymorphism?
• What is dynamic method dispatch in Java?
• Can constructors be polymorphic?
• What does mean by abstraction in java?
• Can you provide examples of where abstraction is effectively used in Java libraries?
• What happens if a class includes an abstract method?
• How does abstraction help in achieving loose coupling in software applications?
• What is interface in Java?
• What is the difference between an interface and an abstract class in Java?
• Can you provide examples of when to use an interface versus when to extend a class?
• How do you use multiple inheritance in Java using interfaces?
• Can an interface in Java contain static methods, and if so, how can they be used?
• When would you use an interface, and when would you use an abstract class?
• Explain the difference between Comparable and Comparator interfaces. When would you use one over the other?
• What is a static method in an Interface, and how is it different from a default method in an interface?
• What is the diamond problem in Java and how does Java address it?
• How does the concept of default methods in interfaces help resolve the diamond problem?
• What does mean by encapsulation in java?
• How Encapsulation Enhances Software Security and Integrity?
• What is the concept of Serialization in Java?
• What is the purpose of the serialVersionUID in Java serialization?
• What happens if the serialVersionUID of a class changes during deserialization?
• How can you prevent certain fields from being serialized in Java?
• Can a class be serialized if one of its member fields is not serializable?
• What is the difference between writeObject() and readObject() methods in Java serialization?
• Is it possible to serialize static fields in Java? Why or why not?
• How do you serialize an object with circular references in Java?
• What is method overloading in Java?
• How does the Java compiler determine which overloaded method to call?
• Is it possible to overload methods that differ only by their return type in Java?
• What are the rules for method overloading in Java?
• What is method overriding in Java?
• What are the rules and conditions for method overriding in Java?
• How does the @Override annotation influence method overriding?
• What happens if a superclass method is overridden by more than one subclass in Java?
• What is 'this' and 'super' keyword in java?
• Can 'this' keyword be assigned a new value in Java?
• What happens if you attempt to use the "super" keyword in a class that doesn't have a superclass?
• Can the this or super keyword be used in a static method?
• How does 'super' play a role in polymorphism?
• What is the static keyword in Java?
• Can a static block throw an exception?
• Can we override static methods in Java?
• Is it possible to access non-static members from within a static method?
• What is static block?
• Can we print something on console without main method in java?
• What is final keyword in java?
• What are some common use cases for using final variables in Java programming?
• How does the "final" keyword contribute to immutability and thread safety in Java?
• Can you describe any performance considerations related to using final?
• What is functional interfaces?
• Can functional interface extend another interface?
• What are the Advantages of using a functional interface.
• Can you tell me some new features that were introduced in Java 8?
• Why optional class, lambda expressions and stream API were introduced in java 8?
• Difference between filter and map function of stream API?
• Can you tell me some new features that were introduced in Java 11?
• Can you tell me some new features that were introduced in Java 17?
• Can you tell me some new features that were introduced in Java 21?
• Which is faster, traditional for loop or Streams?
• In which scenarios would you prefer traditional for loops and streams?
• Explain intermediate and terminal operations in streams.
• Differences in Interface from Java 7 to Java 8.
• Use of String.join(...) in Java 8?
• What is collection framework in java?
• What are the main interfaces of the Java Collection Framework?
• Can you explain how Iterator works within the Java Collection Framework?
• What are some common methods available in all Collection types?
• How does Java Collection Framework handle concurrency?
• How do you choose the right collection type for a specific problem?
• What enhancements were made to the Java Collection Framework in Java 8?
• What is the difference between Iterator and ListIterator?
• Name of algorithm used by Arrays.sort(..) and Collections.sort(..)?
• How do you store elements in a set to preserve insertion order?
• How do you store elements in a way that they are sorted?
• What's the use case of ArrayList, LinkedList and HashSet?
• How does a HashSet ensure that there are no duplicates?
• Can you describe how hashCode() and equals() work together in a collection?
• Why is it important to override the hashCode method when you override equals? What would be the consequence if we don’t?
• Can you give an example where a TreeSet is more appropriate than HashSet?
• What is the internal implementation of ArrayList and LinkedList?
• Can you explain internal working of HashMap in Java?
• What happens when two keys have the same hash code? How would you handle this scenario?
• How does a HashMap handle collisions in Java?
• Can you please tell me what changes were done for the HashMap in Java 8 because before Java 8 HashMap behaved differently?
• Can we include class as a key in HashMap?
• Can you please explain ConcurrentHashMap?
• How does it (ConcurrentHashMap) improve performance in a multi-threaded environment?
• What is time complexities insertions, deletion and retrieval of HashSet and HashMap?
• What is time complexities insertions, deletion and retrieval of TreeSet and TreeMap?
• What techniques did HashMap, TreeMap, HashSet and TreeSet use internally for performing operations?
• What is a design pattern in Java and why do we use this?
• Can you list and explain a few common design patterns used in Java programming?
• How can design patterns affect the performance of a Java application?
• Which design pattern would you use to manage database connections efficiently in a Java application?
• How do you choose the appropriate design pattern for a particular problem in Java?
• Difference between HashMap and TreeMap.
• In what scenarios would you prefer to use a TreeMap over a HashMap?
• Can we add objects as a key in TreeMap?
• What are SOLID Principles?
• What is a thread in Java and how can we create it?
• Can you explain the lifecycle of a Java thread?
• How would you handle a scenario where two threads need to update the same data structure?
• Can we start thread twice?
• What is the difference between Thread class and Runnable interface in Java?
• What are volatile variables?
• What is thread synchronization and why is it important?
• Can you describe a scenario where you would use wait() and notify() methods in thread communication?
• What challenges might you face with multithreaded programs in Java?
• What is Java Memory Model and how it is linked to threads?
• Can we create a server in Java application without creating Spring or any other framework?
• What is transient?
• What is Exchanger class?
• What is reflection in Java?
• What is the weak reference and soft reference in Java?
• What is Java Flight Recorder?
• Discuss Java Generics.
• What is the difference between Young Generation and Old Generation memory spaces?