Answer: Java is a high-level, object-oriented programming language developed by Sun Microsystems. It is known for its platform independence, as Java programs can run on any device that has the Java Virtual Machine (JVM).
Explain the main features of Java.
Answer: Key features include platform independence, object-oriented, simple and familiar syntax, automatic memory management (garbage collection), and strong type checking.
What is the difference between JDK and JRE?
Answer: JDK (Java Development Kit) is a software development kit used to develop Java applications, while JRE (Java Runtime Environment) is used to run Java applications.
What is the significance of the main method in Java?
Answer: The main method is the entry point of a Java program. It’s where the program starts its execution.
What are the access modifiers in Java?
Answer: Java has four access modifiers: public, private, protected, and default (package-private).
Explain the concept of polymorphism in Java.
Answer: Polymorphism allows objects of different types to be treated as objects of a common type. This can be achieved through method overloading and method overriding.
What is the difference between abstraction and encapsulation?
Answer: Abstraction is the process of hiding the implementation details and showing only the essential features, while encapsulation is the bundling of data and the methods that operate on that data into a single unit.
What is the significance of the ‘static’ keyword in Java?
Answer: ‘static’ is used to create class-level variables and methods that can be accessed without creating an instance of the class.
How does exception handling work in Java?
Answer: Java uses try, catch, and finally blocks for exception handling. Exceptions are objects that represent errors or unexpected situations during runtime.
What is the ‘super’ keyword in Java used for?
Answer: ‘super’ is used to refer to the immediate parent class object. It is used to call the parent class methods, access fields, and invoke the parent class constructor.
Explain the difference between abstract classes and interfaces.
Answer: Abstract classes can have both abstract and concrete methods, while interfaces only have abstract methods. A class can implement multiple interfaces, but it can only inherit from one abstract class.
What is the purpose of the ‘final’ keyword in Java?
Answer: ‘final’ can be used to declare a variable, method, or class. A final variable cannot be changed, a final method cannot be overridden, and a final class cannot be extended.
How is multithreading achieved in Java?
Answer: Multithreading in Java is achieved by extending the Thread class or implementing the Runnable interface.
What is the Java Virtual Machine (JVM)?
Answer: JVM is a virtual machine that enables the execution of Java bytecode. It translates Java bytecode into machine code that can be executed by the computer’s hardware.
Explain the concept of garbage collection in Java.
Answer: Garbage collection is the automatic process of reclaiming the memory used by objects that are no longer reachable in a program. Java uses garbage collection to manage memory automatically.
What is the difference between == and .equals() in Java?
Answer: == is used to compare object references, while .equals() is used to compare the contents of objects. For non-primitive types, it’s common to override the .equals() method.
Explain the concept of the Java Naming and Directory Interface (JNDI).
Answer: JNDI is a Java API that provides naming and directory functionality to Java applications. It enables Java software clients to discover and look up data and objects via a name.
What is a JavaBean?
Answer: A JavaBean is a reusable software component that follows certain conventions regarding its construction, naming, and behavior. It is used to encapsulate many objects into a single object.
What is the difference between HashMap and HashTable in Java?
Answer: Both are used to store key-value pairs, but HashMap is not synchronized and allows null values, whereas HashTable is synchronized and doesn’t allow null values.
Explain the concept of serialization in Java.
Answer: Serialization is the process of converting an object into a byte stream, allowing it to be saved to a file, sent over a network, or stored in a database. Deserialization is the reverse process.
What is the use of the transient keyword in Java?
Answer: The transient keyword is used to indicate that a variable should not be serialized during object serialization. It is often used for sensitive information.
How does the ‘this’ keyword work in Java?
Answer: ‘this’ refers to the current object. It is used to distinguish instance variables from local variables when they have the same name, and to invoke the current object’s method.
What is the purpose of the finally block in Java?
Answer: The finally block is used to ensure that a block of code is always executed, whether an exception is thrown or not. It is often used for cleanup operations.
Explain the difference between method overloading and method overriding.
Answer: Method overloading involves defining multiple methods in the same class with the same name but different parameters. Method overriding occurs when a subclass provides a specific implementation for a method that is already defined in its superclass.
What is the purpose of the static block in Java?
Answer: The static block is used to initialize the static variables of a class. It is executed only once when the class is loaded into memory.
What is the Java Collections Framework?
Answer: The Java Collections Framework provides a set of interfaces and classes to represent and manipulate collections of objects, such as lists, sets, and maps.
Explain the ‘Diamond Problem’ in Java.
Answer: The ‘Diamond Problem’ occurs in languages that support multiple inheritance. In Java, it is resolved by allowing a class to implement multiple interfaces, but only extend one class.
What are anonymous classes in Java?
Answer: Anonymous classes are classes without a name. They are often used for one-time use, such as implementing interfaces or extending classes on the fly.
What is the super() keyword used for in Java?
Answer: super() is used to invoke the constructor of the superclass. It must be the first statement in the constructor of the subclass.
Explain the difference between the StringBuilder and StringBuffer classes.
Answer: Both classes are used to manipulate strings, but StringBuilder is not synchronized, making it more efficient in single-threaded environments, whereas StringBuffer is synchronized, making it thread-safe.
What is the difference between the throw and throws keywords in Java?
Answer: The throw keyword is used to explicitly throw an exception, while the throws keyword is used in method declarations to indicate that the method might throw certain exceptions.
Explain the concept of method reference in Java 8.
Answer: Method reference is a shorthand syntax for lambda expressions, making the code more concise. It allows you to refer to a method without invoking it.
What is the purpose of the volatile keyword in Java?
Answer: The volatile keyword is used to indicate that a variable’s value may be changed by multiple threads simultaneously. It ensures that the variable is always read and written from the main memory.
How does the try-with-resources statement work in Java?
Answer: The try-with-resources statement is used to automatically close resources like files, sockets, or database connections when the try block is exited, reducing the chance of resource leaks.
Explain the Observer design pattern in Java.
Answer: The Observer pattern defines a one-to-many dependency between objects so that when one object changes state, all its dependents are notified and updated automatically.
What is the purpose of the @Override annotation in Java?
Answer: The @Override annotation is used to indicate that a method in a subclass is intended to override a method in its superclass. It helps prevent accidental method signature changes.
What is the difference between the LinkedList and ArrayList classes?
Answer: ArrayList uses a dynamic array, providing fast random access, while LinkedList uses a doubly-linked list, providing fast insertion and deletion at the cost of slower random access.
Explain the concept of the Singleton design pattern in Java.
Answer: The Singleton pattern ensures that a class has only one instance and provides a global point of access to it. It involves a private constructor and a static method to obtain the instance.
What is the purpose of the strictfp keyword in Java?
Answer: The strictfp keyword is used to force floating-point calculations to adhere to the IEEE 754 standard, ensuring consistent behavior across different platforms.
Explain the concept of the Spring Framework.
Answer: Spring is a comprehensive framework for enterprise Java development. It provides support for dependency injection, aspect-oriented programming, and various modules for building scalable and maintainable applications.
How does the Comparator interface differ from the Comparable interface in Java?
Answer: The Comparable interface is used to define the natural ordering of objects, while the Comparator interface allows for defining multiple ways of sorting objects.
What is the purpose of the equals() and hashCode() methods in Java?
Answer: The equals() method is used to compare the content equality of objects, and the hashCode() method returns a hash code value for an object, which is often used in hash-based collections.
Explain the concept of dependency injection in Spring.
Answer: Dependency injection is a design pattern in which the dependencies of a class are provided from the outside. In Spring, it is achieved through constructor injection or setter injection.
What is the purpose of the this() constructor call in Java?
Answer: this() is used to invoke a class’s own constructor. It is often used to avoid code duplication when multiple constructors are present in a class.
Explain the purpose of the ClassLoader in Java.
Answer: The ClassLoader is responsible for loading classes into the Java Virtual Machine. It supports dynamic class loading, which allows classes to be loaded at runtime.
What is the java.lang.StringBuilder class, and how does it differ from String?
Answer: StringBuilder is a mutable sequence of characters, and it is more efficient than String for concatenating multiple strings because it does not create a new object for each concatenation.
Explain the concept of generics in Java.
Answer: Generics in Java allow you to write classes, interfaces, and methods that can operate on any data type while providing compile-time type safety.
What is the purpose of the default method in Java interfaces?
Answer: The default keyword is used to define default methods in interfaces, providing a way to add methods to interfaces without breaking existing implementations.
Explain the concept of the nio package in Java.
Answer: The nio (New I/O) package provides a new set of I/O APIs that offer more features and better performance than the traditional I/O APIs. It includes support for non-blocking I/O operations.
What is the purpose of the Enum type in Java?
Answer: An Enum type is a special data type that represents a set of fixed constants. It provides a way to create named constant values that can be used in place of literal values.
