| What is Java? |
| What
the features of Java? |
| What is JVM? |
| What is JRE? |
| What is JDK? |
| What is the difference between JDK, JRE, and JVM? |
| How does Java achieve platform independence? |
| What is bytecode? |
| What is the main() method? |
| Can we overload the main() method? |
| Can we override the main() method? |
| What are command-line arguments? |
| What are variables in Java? |
| What are primitive data types? |
| What is type casting? |
| What is implicit casting? |
| What is explicit casting? |
| What are operators in Java? |
| What is the difference between == and equals()? |
| What is the difference between = and ==? |
| What is an object? |
| What is a class? |
| What is an instance variable? |
| What is a local variable? |
| What is a static variable? |
| What is a constructor? |
| What is the difference between constructor and method? |
| Can constructors be inherited? |
| Can constructors be private? |
| What is constructor overloading? |
| What is method overloading? |
| What is method overriding? |
| What is polymorphism? |
| What are the types of polymorphism? |
| What is inheritance? |
| What are the types of inheritance? |
| Why does Java not support multiple inheritance with classes? |
| What is encapsulation? |
| What is abstraction? |
| What is an abstract class? |
| What is an interface? |
| What is the difference between abstract class and interface? |
| Can an interface have default methods? |
| Can an interface have static methods? |
| What are marker interfaces? |
| What are access modifiers? |
| What is the difference between public, protected, default, and private? |
| What is the final keyword? |
| What is the finally block? |
| What is finalize()? |
| What is the difference between final, finally, and finalize()? |
| What is the static keyword? |
| What is a static block? |
| Can we override static methods? |
| What is the this keyword? |
| What is the super keyword? |
| What is object cloning? |
| What is shallow copy? |
| What is deep copy? |
| What is the Object class? |
| What are the methods of Object class? |
| What is hashCode()? |
| What is equals() contract? |
| What is toString()? |
| What is the difference between String, StringBuilder, and StringBuffer? |
| Why is String immutable? |
| What is the String Constant Pool? |
| What is intern()? |
| How are strings stored in memory? |
| What is garbage collection? |
| How does Garbage Collector work? |
| What are GC roots? |
| Can garbage collection be forced? |
| What are memory leaks in Java? |
| What is heap memory? |
| What is stack memory? |
| What is Metaspace? |
| What is OutOfMemoryError? |
| What is StackOverflowError? |
| What is exception handling? |
| What is the difference between checked and unchecked exceptions? |
| What is the difference between Error and Exception? |
| What is try-catch-finally? |
| What is try-with-resources? |
| How do you create a custom exception? |
| What is throw? |
| What is throws? |
| Can we catch multiple exceptions? |
| What is multi-catch? |
| What is reflection? |
| What is the Reflection API? |
| What are annotations? |
| What are built-in annotations? |
| What are custom annotations? |
| What is serialization? |
| What is deserialization? |
| What is transient? |
| What is volatile? |
| What is enum? |
| What is var in Java? |
| What are wrapper classes? |
| What is autoboxing and unboxing? |
| What is package? |
| What is import statement? |
| What is package-private access? |
| What is Java Memory Model? |
| What is pass-by-value in Java? |
| What is the difference between compile-time and runtime polymorphism? |
| What is covariant return type? |
| What is anonymous class? |
| What is inner class? |
| What is local inner class? |
| What is static nested class? |
| What is lambda expression? |
| What is functional interface? |
| What is method reference? |
| What are streams in Java? |
| What is Optional? |
| What is record in Java? |
| What is sealed class? |
| What is switch expression? |
| What are text blocks? |
| What are modules in Java? |
| How do you improve Java performance? |
| What are common Java coding best practices? |
| Explain SOLID principles in Java. |
| What are common Java interview coding questions? |
| How do you debug Java applications? |
| What are JVM arguments? |
| What are JVM startup options? |
| Explain Java execution flow from source code to bytecode. |
| Explain the class loading process in Java. |
| What are ClassLoaders? |
| What is Bootstrap ClassLoader? |
| What is Extension ClassLoader? |
| What is Application ClassLoader? |
| What is dynamic class loading? |
| How do you prevent object creation? |
| What is Singleton class? |
| How do you implement Singleton in Java? |
| What are immutable classes? |
| How do you create an immutable class? |
| What are design patterns commonly used in Java? |
| Explain Factory Pattern. |
| Explain Builder Pattern. |
| Explain Strategy Pattern. |
| Explain Observer Pattern. |
| What are Java 8 features? |
| What are Java 11 features? |
| What are Java 17 features? |
| What are Java 21 features? |
| What are the most frequently asked Core Java interview questions for experienced developers? |
| What is the Java Memory Model (JMM)? |
| Explain happens-before relationship in Java. |
| What is safe publication of objects? |
| What is escape analysis? |
| What is TLAB (Thread Local Allocation Buffer)? |
| What is object header in Java? |
| What is compressed OOPs? |
| How is memory allocated for objects? |
| What happens when new keyword is executed? |
| How does Java allocate arrays in memory? |
| What is class loading? |
| Explain the delegation model of ClassLoader. |
| What is custom ClassLoader? |
| When is a class initialized? |
| Difference between loading, linking, and initialization? |
| What is class unloading? |
| Can classes be unloaded from JVM? |
| What is static initialization order? |
| What is instance initialization block? |
| Execution order of constructors, static blocks, and instance blocks? |
| Difference between Comparable and Comparator? |
| How does compareTo() work? |
| How does Comparator chaining work? |
| What is natural ordering? |
| What is custom sorting? |
| What is immutable object? |
| Why should immutable classes be final? |
| Can immutable classes contain mutable fields? |
| How do you make defensive copies? |
| Advantages of immutable objects? |
| Difference between StringBuilder and StringBuffer? |
| Why is String immutable? |
| How is String Pool implemented? |
| Difference between new String() and string literal? |
| How does intern() work? |
| Can String Pool cause memory issues? |
| Explain hashCode() and equals() contract. |
| What happens if hashCode() is not overridden? |
| Can two unequal objects have same hashCode()? |
| Can equal objects have different hashCode()? |
| How do HashMap and equals() work together? |
| Explain finalize() deprecation. |
| What is Cleaner API? |
| What are Weak References? |
| What are Soft References? |
| What are Phantom References? |
| Difference between WeakHashMap and HashMap? |
| What are JVM memory regions? |
| Difference between Heap and Metaspace? |
| What is Eden Space? |
| What are Survivor Spaces? |
| What is Old Generation? |
| Explain Minor GC. |
| Explain Major GC. |
| Explain Full GC. |
| What causes Full GC? |
| How do you analyze GC logs? |
| Difference between Serial GC, Parallel GC, CMS, G1, ZGC, and Shenandoah? |
| What is G1 Garbage Collector? |
| What is ZGC? |
| What is Shenandoah GC? |
| When should you use Parallel GC? |
| Explain reflection with example. |
| What are drawbacks of Reflection? |
| How do you invoke methods using Reflection? |
| How do frameworks use Reflection? |
| Can private methods be invoked using Reflection? |
| What are annotations? |
| Difference between RetentionPolicy values? |
| What are meta-annotations? |
| How do custom annotations work? |
| What is @Inherited annotation? |
| Difference between checked and unchecked exceptions? |
| Can overridden methods throw broader exceptions? |
| Can constructors throw exceptions? |
| How does exception propagation work? |
| Best practices for exception handling? |
| What is serialization? |
| How does Serializable work internally? |
| What is serialVersionUID? |
| What happens if serialVersionUID changes? |
| What is Externalizable? |
| Difference between Serializable and Externalizable? |
| Explain transient keyword. |
| Explain volatile keyword. |
| Difference between transient and volatile? |
| What are lambda expressions? |
| How are lambda expressions implemented internally? |
| What is invokedynamic? |
| Difference between lambda and anonymous class? |
| What is functional interface? |
| Explain Optional class. |
| Difference between orElse() and orElseGet()? |
| What is Optional.flatMap()? |
| Common mistakes while using Optional? |
| Explain Java Streams. |
| Difference between map() and flatMap()? |
| Difference between filter() and peek()? |
| Difference between limit() and skip()? |
| Difference between findAny() and findFirst()? |
| Difference between reduce() and collect()? |
| What is Collector? |
| How does parallelStream() work? |
| When should parallel streams be avoided? |
| Explain var keyword. |
| What are records? |
| What are sealed classes? |
| What are text blocks? |
| Explain pattern matching in Java. |
| What are switch expressions? |
| What are modules in Java? |
| Explain module-info.java. |
| Benefits of Java Modules? |
| What is Process API? |
| What is VarHandle? |
| What is MethodHandle? |
| Difference between Reflection and MethodHandle? |
| Explain JVM architecture. |
| How does JIT compiler work? |
| What is HotSpot JVM? |
| What is C1 and C2 compiler? |
| What is GraalVM? |
| How do you troubleshoot OutOfMemoryError? |
| How do you analyze heap dumps? |
| How do you identify memory leaks? |
| How do you profile Java applications? |
| What tools do you use for JVM monitoring? |
| Difference between fail-fast and fail-safe iterators? |
| How does ConcurrentModificationException occur? |
| What is modCount? |
| Explain Java coding best practices. |
| What are common Core Java interview coding questions? |
| What are common Java performance tuning techniques? |
| What are common Java design mistakes? |
| What are the most frequently asked Core Java interview questions for 10+ years experienced developers? |
| What is Object-Oriented Programming, and what problems does it solve? |
| What are the four fundamental principles of OOP? |
| What is the difference between a class and an object? |
| What is encapsulation, and why is it important? |
| How do you achieve encapsulation in Java? |
| What is abstraction, and how is it different from encapsulation? |
| How do abstract classes support abstraction? |
| How do interfaces support abstraction? |
| What is inheritance, and why is it used? |
| What are the different types of inheritance? |
| Why does Java not support multiple inheritance through classes? |
| How can Java achieve multiple inheritance using interfaces? |
| What is polymorphism? |
| What is compile-time polymorphism? |
| What is runtime polymorphism? |
| What is method overloading? |
| What is method overriding? |
| What is the difference between method overloading and method overriding? |
| Can a static method be overridden? |
| Can a private method be overridden? |
| Can a final method be overridden? |
| What is dynamic method dispatch? |
| What is upcasting in OOP? |
| What is downcasting, and what risks are associated with it? |
| What is the difference between IS-A and HAS-A relationships? |
| What is composition? |
| What is aggregation? |
| What is the difference between composition and aggregation? |
| Why is composition often preferred over inheritance? |
| What is association in OOP? |
| What is dependency in object-oriented design? |
| What is object coupling? |
| What is cohesion? |
| Why should high cohesion and low coupling be preferred? |
| What is an immutable object? |
| How do you design an immutable class in Java? |
| Why is String immutable in Java? |
| What is the role of constructors in object creation? |
| Can constructors be inherited or overridden? |
| What is constructor chaining? |
| What is the difference between this and super? |
| What is the difference between an abstract class and an interface? |
| When would you choose an abstract class over an interface? |
| When would you choose composition over inheritance? |
| What is the Open/Closed Principle? |
| What is the Single Responsibility Principle? |
| What is the Liskov Substitution Principle? |
| What is the Interface Segregation Principle? |
| What is the Dependency Inversion Principle? |
| How do SOLID principles improve object-oriented design? |
| What is the difference between abstraction and polymorphism? |
| How does encapsulation improve maintainability? |
| How does inheritance affect coupling? |
| What are the disadvantages of excessive inheritance? |
| What is the fragile base class problem? |
| What is the diamond problem in multiple inheritance? |
| How does Java resolve default method conflicts in interfaces? |
| What happens when two interfaces contain the same default method? |
| What is the difference between an object reference and an object? |
| What happens internally when an object is created using new? |
| What is object identity versus object equality? |
| What is the contract between equals() and hashCode()? |
| Why should equals() and hashCode() be overridden together? |
| What is shallow copying? |
| What is deep copying? |
| How does cloning relate to OOP design? |
| What is an interface in Java? |
| What is an abstract class in Java? |
| What is the difference between an interface and an abstract class? |
| When should you use an interface instead of an abstract class? |
| When should you use an abstract class instead of an interface? |
| Can an interface contain concrete methods? |
| What are default methods in interfaces? |
| What are static methods in interfaces? |
| Can an interface have private methods? |
| Can an interface have constructors? |
| Can an abstract class have constructors? |
| Can an abstract class contain both abstract and concrete methods? |
| Can an abstract class contain instance variables? |
| Can an interface contain variables? |
| Why are interface variables implicitly public, static, and final? |
| Can an interface extend another interface? |
| Can an interface extend multiple interfaces? |
| Can an abstract class implement an interface? |
| Can an abstract class extend another abstract class? |
| Can a concrete class extend an abstract class and implement an interface? |
| Can a class implement multiple interfaces? |
| Why does Java support multiple inheritance through interfaces? |
| What is the diamond problem with interfaces? |
| How does Java resolve conflicting default methods? |
| What happens when two interfaces provide the same default method? |
| Can a class override a default method from an interface? |
| Can an interface extend an interface containing default methods? |
| Can an abstract class implement an interface without implementing all methods? |
| What happens if a concrete class does not implement all interface methods? |
| Can an interface contain abstract methods without the abstract keyword? |
| Are interface methods public by default? |
| What is the visibility requirement when implementing an interface method? |
| Can an interface method be protected or private? |
| Can an abstract class method be private? |
| Can an abstract method be static? |
| Can an abstract method be final? |
| Can an abstract class be final? |
| Can an interface be final? |
| Can an interface be instantiated? |
| Can an abstract class be instantiated? |
| Can an interface reference point to an implementing class object? |
| What is interface-based programming? |
| How does programming to an interface reduce coupling? |
| How do interfaces support polymorphism? |
| How does an abstract class support code reuse? |
| What is the difference between abstraction and implementation hiding? |
| How do interfaces help achieve loose coupling? |
| How do interfaces support dependency inversion? |
| How are interfaces used with dependency injection in Spring? |
| What is a functional interface? |
| What is the purpose of the @FunctionalInterface annotation? |
| Can a functional interface contain default and static methods? |
| Can a functional interface extend another interface? |
| What happens if a functional interface contains two abstract methods? |
| What is a marker interface? |
| What are examples of marker interfaces in Java? |
| What is the difference between a marker interface and an annotation? |
| What is a sealed interface? |
| What is a sealed abstract class? |
| How do sealed classes and interfaces control inheritance? |
| What is the difference between sealed, non-sealed, and final classes? |
| Can an interface extend a sealed interface? |
| Can an abstract class implement a sealed interface? |
| How would you design an extensible API using interfaces? |
| How would you design a common base workflow using an abstract class? |
| How does the Template Method pattern relate to abstract classes? |
| Why are interfaces commonly preferred for contracts? |
| What are the limitations of abstract classes? |
| What are the limitations of interfaces? |
| How have interfaces evolved from Java 7 to Java 8, 9, 11, 17, and 21? |
| What changed for interfaces in Java 8? |
| What changed for interfaces in Java 9? |
| Can an interface have private methods in modern Java? |
| Can an interface have static initialization blocks? |
| Can an abstract class contain static methods and variables? |
| Can an abstract class implement multiple interfaces? |
| Can an interface inherit methods from Object? |
| Can an interface override equals(), hashCode(), or toString()? |
| What happens if an interface declares a default method with the same signature as Object? |
| How does method resolution work between superclass and interface default methods? |
| What happens when a superclass and interface provide methods with the same signature? |
| Can two unrelated interfaces have methods with the same name and parameters? |
| How does Java handle covariant return types in interface implementations? |
| Can an interface method throw checked exceptions? |
| Can an implementing class reduce the checked exceptions declared by an interface method? |
| Can an implementing class change the return type of an interface method? |
| What is the difference between inheritance and interface implementation? |
| What is the difference between extends and implements? |
| Can a class extend one class and implement multiple interfaces? |
| Can an interface inherit state from another interface? |
| How would you migrate an abstract class design to interfaces? |
| How do interfaces improve testability and mocking? |
| When can excessive use of interfaces become a design problem? |
| How would you choose between interface, abstract class, and concrete class in a real project? |
