(1).pngL.jpg)
Common Java Interview Questions
Q. Why is Java a platform-independent language?
Q. Why can Java not be a pure object-oriented language?
Q. Is Java a completely object-oriented programming language?
Java is arguably the complete object-oriented language. You can access every Java component since they come under classes, by creating these objects.
However, from another perspective, Java isn’t the complete package as an object-oriented programming language. According to this line of thinking, Java isn’t complete since it can directly access primitive types of data. This primitive data doesn’t belong directly to any integer classes.
Q. How are Java and C++ different?
- C++ is a compiled programming language, while Java is both interpreted and compiled.
- C++ programs can run in just the machines where they have been compiled, while Java programs are system-independent.
- While using C++, a user can use pointers in the program, which isn’t allowed with Java. Java uses pointers internally.
- C++ supports multiple inheritances as a concept while Java doesn’t. Moreover, avoiding the name ambiguity complexity results in the diamond problem.
Q. C and C++ use pointers. Why doesn’t Java use any?
A pointer is unsafe and complicated for new programmers to use. Java is more focused on simplifying code, which can become a challenge with pointers. Using pointers can also result in errors and compromise security by allowing users to access memory directly. Additionally, not using pointers with Java furnishes a new level of abstraction in the program. Additionally, using pointers makes the garbage collection process erroneous and slow. Java uses references instead as pointers can be manipulated, but references can’t.
Q. What are the default values of instances and variables in Java?
- Java variables have no default values. Developers need to initialise or enter values before using instances, else it could add compilation errors. In some situations, variables don’t need to be initialised.
- However, if you create this object, the default constructor initialises the default value depending on the type of data.
- If the object is a reference, it is assigned a Null value.
- If the object is numeric, it is assigned 0 as a value.
- If the object is a boolean, the value assigned is ‘False’.
Q. What do you know about data encapsulation?
Data encapsulation can be described as a programming concept that is object-oriented and hides data attributes as well as their behaviours in unique units. Through data encapsulation, developers can follow modularity as they develop software. They ensure every object remains independent of the others through unique attributes, functionalities and methods for every object. The primary use of data encapsulation is to secure an object’s private properties and thus enable data hiding.
Q. What are the major benefits of using Java?
Q. What is meant by Class and Object?
Q. What do JRE, JDK, and JVM imply?
Q. Does all property of Immutable Objects have to be finalized?
Q. What does looping imply?
Q. What is the key difference between Overriding and Overloading?
Q. What does Inheritance imply?
Q.What is the JIT compiler?
Q. Is restricting Inheritance possible?
Q.What is meant by Content Negotiation?
Q. What does WORA mean?
Q. How can deadlock be avoided in Java?
Q. Why is a constructor important?
Q. Is it possible to override static methods?
Q. What would be the core objective of garbage collection?
Q.What shall be the use of composition?
Q. What is meant by annotation?
Q. When it comes to storing confidential data, why is character array usually opted for over string?
Q. Which components do you find in a Java download file? Are they the same or do they have differences?
Every Java Download file has two components.
- Java Development Kit or JDK
- Java Runtime Environment or JRE
There are several differences between them both, which is as follows:
Q. What is a classloader?
In Java, classloaders are a Java Virtual Machine subsystem, which focuses on loading class files. Once a program gets executed, the classloader takes the first step toward loading executable files. The classloaders in Java are Bootstrap, Application and Extension.
Q. Which memory allocations does Java have?
There are five leading memory allocation types.
- Class memory
- Stack memory
- Heap memory
- Native method stack memory
- Program counter-memory
Q. Are there any differences between Stack and Heap memory?
There are fundamental differences between Stack and Heap memory. Stack Memory is typically used for storing local variables and the method execution order. Meanwhile, Heap memory stores objects securely. Once both these types of memories store information, dynamic memory reallocation and allocation are used.
Q. Can a program run if you write ‘static public void main’ as a command?
In Java, there are no rules regarding specifiers that say they need to follow a particular order. So the program can run effectively with this command.
Q. What is the default value that Local Variables store?
There are no default values stored in either Local Variables or any primitive or object references.
Q. What is an Association?
An Association can be understood as a relationship where one component or object has no ownership of the other. For instance, one person can have multiple bank accounts and a bank can have multiple customers. However, neither one owns the other.
Q. What does aggregation mean?
Aggregation can be understood as the bond between two classes. It can best be described as a ‘has-a’ and ‘whole/part’ relationship. An aggregation is a highly-specialised type of association relationship. The reference of another class is contained in an aggregation and it also owns that class.
Q. What is a Copy Constructor in Java?
In Java, a Copy Constructor is the constructor responsible for initialising one object through a second object belonging to the same class.
Q. What is a marker interface?
In Java, any empty interface is known as a Marker interface. Well-known examples of a Marker Interface are Cloneable and Serializable.
Q. What is Object Cloning in Java?
Object Cloning refers to the ability to recreate entire objects to mimic another existing object in Java. Java provides a method called clone() that enables the cloning of an existing object that will offer the same functionality as the one that already exists.
Q. What is an object-oriented paradigm?
Object-oriented paradigms function according to the Objects concept and are made up of code and data. The data is contained as fields while regulation is contained as procedures. The most prominent feature object-oriented paradigms have is that the procedures of an object can access and modify the fields of data themselves.
Q. What are Wrapper Classes in Java?
When a programmer declares a primitive data type in Java, a Wrapper class is responsible for converting the data types into objects.
Q. What is a Singleton Class in Java?
When a programmer makes a class’ constructor private in Java, that class can only generate one object. This class is what developers call a Singleton Class.
Q. Define a Java package.
A package bundles together several interfaces and classes as well as the necessary JAR files and libraries. A package in Java helps reuse code.
Q. Can you implement a pointer while using Java?
A Java VM implicitly helps in managing memory. The primary objective behind developing Java was to simplify programming. For this reason, accessing any memory or data directly using pointers is not recommended since it complicates the process. Thus, you cannot implement pointers in Java.
Q. Distinguish between local and instance variables.
Any variable is declared within a class, where the scope remains limited to one specific object. Local variables are contained within a method or a specific code block. Additionally, the scope remains limited to a code segment with a declared variable.
Q. What do you know about Java String Pool?
Java String Pool is defined as a collection of strings within the Heap memory in Java. If you attempt to create any new string object, JVM tries to first locate a new object’s presence within the pool. If the object is available, the same object reference gets shared with this variable, otherwise a new object gets created.
Q. What is an exception in the context of Java?
In Java, any unexpected event that disrupts the normal flow of a program is called an exception. You can fix these events using the Exception Handling process.
Q. What will happen if the main() is not declared static?
If the main method isn’t declared static, the program can be correctly compiled but could end up with severe ambiguity. As a result, it throws up an error message that says ‘NoSuchMethodError’.
All these questions are not guaranteed to come in your next Java interview. These are the core Java interview questions that show you the level of questions that you can expect as well as how you should frame your answers when asked. There are several instances where candidates know the answer but stutter or lose confidence because they cannot frame their answer right.
To train with industry experts and prepare for your interview with professional mentors, enrol in a training course on Koenig today.
COMMENT