Java Interview Questions and Answers for Freshers

Practice here the most popular Core Java Interview Questions and Answers, which asked many times in Java Interview.

What is Java?
Answer: Java is a high-level, object-oriented programming language that is designed to be platform-independent, meaning that code written in Java can run on any machine that has a Java Virtual Machine (JVM).

What is an object in Java?
Answer: An object is an instance of a class that has state and behavior.

What is a class in Java?
Answer: A class is a blueprint or template for creating objects.

What is the difference between a class and an object?
Answer: A class is a blueprint or template for creating objects, while an object is an instance of a class.

What is the difference between a constructor and a method in Java?
Answer: A constructor is a special type of method that is used to initialize the object's state, while a method is a regular function that performs some action on the object.

What is the difference between an abstract class and an interface in Java?
Answer: An abstract class is a class that cannot be instantiated and may contain both abstract and concrete methods, while an interface is a collection of abstract methods and constants.

What is Java?
Answer: Java is a high-level, object-oriented programming language that is designed to be platform-independent, meaning that code written in Java can run on any machine that has a Java Virtual Machine (JVM).

What is an object in Java?
Answer: An object is an instance of a class that has state and behavior.

What is a class in Java?
Answer: A class is a blueprint or template for creating objects.

What is the difference between a class and an object?
Answer: A class is a blueprint or template for creating objects, while an object is an instance of a class.

What is the difference between a constructor and a method in Java?
Answer: A constructor is a special type of method that is used to initialize the object's state, while a method is a regular function that performs some action on the object.

What is the difference between an abstract class and an interface in Java?
Answer: An abstract class is a class that cannot be instantiated and may contain both abstract and concrete methods, while an interface is a collection of abstract methods and constants.

What is inheritance in Java?
Answer: Inheritance is a mechanism in which one class acquires the properties and behaviors of another class.

What is the difference between method overloading and method overriding in Java?
Answer: Method overloading is when two or more methods have the same name but different parameters, while method overriding is when a subclass provides a specific implementation for a method that is already provided by its parent class.

What is the final keyword in Java?
Answer: The final keyword can be used to mark a class, method, or variable as immutable or unchangeable.

What is the static keyword in Java?
Answer: The static keyword can be used to mark a class, method, or variable as belonging to the class rather than to a specific instance of the class.

What is encapsulation in Java?
Answer: Encapsulation is the process of hiding the implementation details of a class and providing a public interface for accessing the class's properties and methods.

What is polymorphism in Java?
Answer: Polymorphism is the ability of an object to take on many forms, meaning that an object can be used as if it is of many different types.

What is the difference between a StringBuffer and a StringBuilder in Java?
Answer: A StringBuffer is thread-safe and synchronized, while a StringBuilder is not.

What is the difference between a checked and an unchecked exception in Java?
Answer: A checked exception is a type of exception that must be declared in a method or caught by a try-catch block, while an unchecked exception is a type of exception that does not need to be declared or caught.

What is the difference between a stack and a queue in Java?
Answer: A stack is a last-in, first-out (LIFO) data structure, while a queue is a first-in, first-out (FIFO) data structure.

What is the difference between a HashSet and a TreeSet in Java?
Answer: A HashSet is an unordered collection of unique elements, while a TreeSet is an ordered collection of unique elements.

What is a lambda expression in Java?
Answer: A lambda expression is a concise way of expressing an anonymous function in Java.

What is the difference between a stream and a collection in Java?
Answer: A stream is a sequence of elements that can be processed in parallel or sequentially, while a collection is a group of elements that can be accessed and modified.
Answer: Inheritance is a mechanism in which one class acquires the properties and behaviors of another class.

What is the difference between method overloading and method overriding in Java?
Answer: Method overloading is when two or more methods have the same name but different parameters, while method overriding is when a subclass provides a specific implementation for a method that is already provided by its parent class.

What is the final keyword in Java?
Answer: The final keyword can be used to mark a class, method, or variable as immutable or unchangeable.

What is the static keyword in Java?
Answer: The static keyword can be used to mark a class, method, or variable as belonging to the class rather than to a specific instance of the class.

What is encapsulation in Java?
Answer: Encapsulation is the process of hiding the implementation details of a class and providing a public interface for accessing the class's properties and methods.

What is polymorphism in Java?
Answer: Polymorphism is the ability of an object to take on many forms, meaning that an object can be used as if it is of many different types.

What is the difference between a StringBuffer and a StringBuilder in Java?
Answer: A StringBuffer is thread-safe and synchronized, while a StringBuilder is not.

What is the difference between a checked and an unchecked exception in Java?
Answer: A checked exception is a type of exception that must be declared in a method or caught by a try-catch block, while an unchecked exception is a type of exception that does not need to be declared or caught.

What is the difference between a stack and a queue in Java?
Answer: A stack is a last-in, first-out (LIFO) data structure, while a queue is a first-in, first-out (FIFO) data structure.

What is the difference between a HashSet and a TreeSet in Java?
Answer: A HashSet is an unordered collection of unique elements, while a TreeSet is an ordered collection of unique elements.

What is a lambda expression in Java?
Answer: A lambda expression is a concise way of expressing an anonymous function in Java.

What is the difference between a stream and a collection in Java?
Answer: A stream is a sequence of elements that can be processed in parallel or sequentially, while a collection is a group of elements that can be accessed and modified.

What is a thread in Java?
Answer: A thread is a lightweight process that can be executed independently and concurrently with other threads within the same program.

What is synchronization in Java?
Answer: Synchronization is the process of ensuring that multiple threads do not simultaneously execute a critical section of code, which can lead to race conditions and other issues.

What is the difference between a private and a protected method in Java?
Answer: A private method can only be accessed within the same class, while a protected method can be accessed within the same class and its subclasses.

What is the difference between a local variable and an instance variable in Java?
Answer: A local variable is a variable that is declared within a method and has a limited scope, while an instance variable is a variable that is declared within a class and is accessible to all methods of the class.

What is the difference between a float and a double in Java?
Answer: A float is a single-precision floating-point number that takes up 32 bits of memory, while a double is a double-precision floating-point number that takes up 64 bits of memory.

What is a package in Java?
Answer: A package is a grouping of related classes and interfaces that provide a namespace to avoid naming conflicts.

What is a constructor chaining in Java?
Answer: Constructor chaining is the process of calling one constructor from another constructor of the same class using the "this" keyword.
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