Java Interview Questions
Here is a resource that provides a collection of commonly asked questions in Java job interviews. The page includes questions on a wide range of Java topics, including core Java concepts, object-oriented programming, collections, multithreading, exception handling, and more.
The questions are designed to test the knowledge and understanding of Java developers at different levels, from entry-level positions to senior and architect roles. Each question is accompanied by a brief explanation or sample code that illustrates the concept being tested.
The Java Interview Questions are valuable resource for job seekers preparing for Java job interviews, as well as for hiring managers looking to evaluate the technical skills of candidates. The questions cover a broad range of topics and are designed to assess both the depth and breadth of a candidate's knowledge of Java programming.
What is Java?
Java is a high-level programming language known for its platform independence, object-oriented features, and its use in building a wide range of applications.
What Is a Package in Java?
A package in Java is a way to organize classes and interfaces into a single unit, providing better modularity, encapsulation, and reducing naming conflicts.
What is WORA?
WORA stands for "Write Once, Run Anywhere." It is a principle in Java where code written on one platform can be executed on any other platform without modification.
What is bytecode?
Bytecode in Java is an intermediate code generated by the Java compiler. It is platform-independent and can be executed by the Java Virtual Machine (JVM).
Define JIT compiler in Java?
JIT (Just-In-Time) compiler in Java is responsible for translating Java bytecode into native machine code at runtime, which leads to improved performance of Java applications.
What are primitive data types?
Primitive data types in Java are the basic data types provided by the language itself, such as int, double, boolean, etc., which store simple values like numbers and characters.
Is there any default value for local variables?
Yes, local variables in Java are assigned default values if they are not explicitly initialized. For example, numeric types are set to 0, booleans to false, and object references to null.
Can you overload main() method in Java?
Yes, you can overload the main() method in Java by providing different method signatures, but the JVM will only consider the standard main method with the exact signature for program execution.
What Is the void Type and When Do you Use It?
In Java, the void type indicates that a method does not return any value. It is used when a method performs an action but doesn't produce a result to be used in the calling code.
Why are there no global variables in Java?
Java follows a strong object-oriented design, and global variables can lead to uncontrolled dependencies and reduced encapsulation. Instead, Java encourages encapsulation through class members and appropriate access modifiers.
Define Object in Java?
In Java, an object is an instance of a class that represents a real-world entity or data. Objects encapsulate data and behavior and form the foundation of object-oriented programming.
Can you override a static method in Java?
No, static methods in Java are associated with the class itself and not with individual instances. Therefore, they cannot be overridden, but they can be hidden by declaring a static method with the same signature in a subclass.
Which class is the superclass for all the classes in Java?
The Object class is the superclass for all the classes in Java. Every class implicitly or explicitly inherits from the Object class.
What is the super keyword in Java?
The super keyword in Java is used to refer to the superclass, allowing access to its methods and constructors. It is often used to call the superclass constructor from a subclass constructor or to access overridden methods.
What are the differences between an Inner Class and a Sub-Class?
An inner class is a class defined within another class, whereas a subclass (also known as a derived class) is a new class that inherits from an existing class. Inner classes have access to the members of the outer class, while subclasses inherit members from the superclass.
What is the default size of the load factor in the hashing-based collection?
The default load factor in Java's hashing-based collection classes (like HashMap) is 0.75. The load factor determines the threshold at which the collection will resize itself to maintain a balance between space and performance.
Is there any need to import java.lang package?
No, there is no need to import the java.lang package explicitly because it is automatically imported by the Java compiler for all Java programs. It contains fundamental classes like String, Object, and System that are used in almost every Java program.
Is JDK required on each machine to run a Java program?
No, JDK (Java Development Kit) is not required on each machine to run a Java program. You only need the JRE (Java Runtime Environment) on the target machine, which is a subset of the JDK and is used to execute Java applications.
How can I convert my Java program to an .exe file?
You can convert a Java program to an .exe file using third-party tools like "launch4j" or "exe4j." These tools bundle your Java program with a Java Runtime Environment (JRE) and create an executable file for Windows.
How many types of memory areas are allocated by JVM?
JVM (Java Virtual Machine) allocates memory in five main areas: Method Area, Heap, Java Stack, PC Register, and Native Method Stack. These areas are used to manage and execute Java programs efficiently.
What is Class.forName()?
Class.forName() is a method used to dynamically load a class at runtime. It loads the class into the JVM and returns a Class object representing the loaded class, allowing you to work with it programmatically.
How to prevent a method from being overridden?
To prevent a method from being overridden in Java, you can declare the method as final. A final method cannot be overridden by any subclass, ensuring its behavior remains consistent across the inheritance hierarchy.
Last Updated : 28 July 2023