Top Java Interview Questions And Answers

Program Explanation:

• Here, we have two objects str1 and num. These two belong to different classes, i.e. string class and integer class.

• Thus, using the equals() method, we get the output as false.

The image below represents the output of the above Java program.

Question 18. What Is The Java String Pool?

The Java string pool is where all the strings defined in a Java program are stored. It is a part of the heap memory. When a new string object is created, the JVM checks if it is present in the string pool or not.

The same object reference is given with the new variable if it is present. Otherwise, a new string object is created.

Question 19. What Is The Difference Between Instance Variables And Local Variables?

Below is the difference between instance variables and local variables:

Instance variable: An instance variable is created outside the method. The instance variable is invoked by the class directly. Instance variables have a default value and can be used throughout the class.

Local variable: A local variable is created or declared within the method. Local variables have no default value and their scope is also limited to the method.

Question 20. Differentiate Between Java Abstract Class And Java Interface.

Abstract class: An abstract class in Java includes abstract methods, non-abstract methods, and even final methods. It does not support multiple inheritance. Abstract class data members can have different access modifiers like public, protected, private, etc.

Interface class: A Java interface includes only abstract methods. It supports multiple inheritance. The data members of a Java interface are public by default.

Question 21. Explain The Difference Between Heap And Stack Memory

Heap memory: It is used for dynamic memory allocation. Here, objects and instance variables are stored in a heap. The memory management in this case is handled by the garbage collector.

Stack memory: The stack memory is used to store the temporary variables that are created when a method is invoked (function call.) Just like the stack data structure, it also follows the Last-In-First-Out (LIFO) approach.

Question 22. What Are Class Variables In Java?

Class variables can be declared using the static keyword. They can be created anywhere at the class level and can only have a single value when applied to different objects. These are not associated with a specific object and hence are shared by all the members of a class.

Question 23. Explain The Line public static void main(string args[]) in Java.

In Java, the main function is declared using public static void main(string args[]). Below is the breakdown of its syntax:

public: It is used as an access modifier. It makes the main function globally available.

static: Static is the keyword that helps us prevent unnecessary allocation of memory.

void: Void in void main( string args[]) represents the return type of the main function. It depicts that the function does not return anything.

string args: It is used to store the command line arguments.

Question 24. Can We Override Static Methods?

No, we cannot override static methods as they are associated with the class itself and not a specific object of the class.

Question 25. What Is Dynamic Method Dispatch In Java?

In Java programming language, the process when a function call is made during the runtime rather than the compile time is said to be dynamic method dispatch. We can also refer to it as run-time polymorphism.

Question 26. Explain The Concept Of Method Overloading.

Method overloading, in Java, happens when we create multiple method signatures using the same name of a method. We can achieve method overloading by either changing the number of arguments a method takes or by changing the return type of the method.

Question 27. Describe The Concept Of Method Overriding In Java.

Method overriding occurs when two or more methods having the same signatures are present in different Java classes. We usually see it in inheritance and runtime polymorphism.

We need to take care of a few things while performing method overriding. The overridden methods are required to have the same method signature, return type, and argument list. In method overriding, there should be no restricted access between the methods.

Question 28. What Is An Instance Method?

An instance method in Java is a function that is associated with an instance, i.e., an object rather than a class. They can be used to call a specific instance of a class by using object references.

Question 29. What Do You Understand By Object Cloning?

The process of object cloning in Java is used to recreate a new object that is the same as an existing Java class object. The clone() method provided by Java is used for this purpose.

We’ve written a detailed article on git cloning into the existing directory.

Question 30. What Is An Access Modifier In Java?

An access modifier is a keyword that lets us know how can we access a particular variable, object, or function in Java. For example, variables having a private access modifier can only be accessed within the particular block it is declared.

Question 31. What Is Exception Handling In Java?

Sometimes, our Java program may encounter some errors while running the program that may terminate the program execution. Such an error is called a runtime exception. Writing a piece of code to tackle such exceptions is known as exception handling.