Common Java Interview Questions

1.What is JVM?

The Java interpreter along with the runtime environment required to run the Java application in called a Java virtual machine(JVM)


2. What is the most important feature of Java?

Java is a platform-independent language.


3. What do you mean by platform independence?

Platform independence means that we can write and compile the java code in one platform (eg Windows) and can execute the class in any other supported platform eg (Linux, Solaris,etc).


4. What is the difference between a JDK and a JVM?

JDK is Java Development Kit which is for development purposes and it includes an execution environment also. But JVM is purely a run time environment and hence you will not be able to compile your source files using a JVM.


5. What is the base class of all classes?

java.lang.Object


6. What are the access modifiers in Java?

There are 3 access modifiers. Public, protected, and private, and the default one if no identifier is specified is called friendly, but the programmer cannot specify the friendly identifier explicitly.


7. What is are packages?

A package is a collection of related classes and interfaces providing access protection and namespace management.


8. What is meant by Inheritance and what are its advantages?

 Inheritance is the process of inheriting all the features from a class. The advantages of inheritance are reusability of code and accessibility of variables and methods of the superclass by sub classes.


9. What is the difference between superclass and subclass?

 A super class is a class that is inherited whereas sub class is a class that does the inheriting.


10. What is an abstract class?

An abstract class is a class designed with implementation gaps for subclasses to fill in and is deliberately incomplete.


11. What are the states associated with the thread?

The thread contains ready, running, waiting, and dead states.


12. What is synchronization?

Synchronization is the mechanism that ensures that only one thread is accessed the resources at a time.


13. What is deadlock?

When two threads are waiting for each other and can’t precede the program is said to be deadlock.


14. What is an applet?

The applet is a dynamic and interactive program that runs inside a web page displayed by a java capable browser


15. What is the lifecycle of an applet?

init() method – Can be called when an applet is first loaded

start() method – Can be called each time an applet is started.
paint() method – Can be called when the applet is minimized or maximized.
stop() method – Can be used when the browser moves off the applet’s page.
destroy() method – Can be called when the browser is finished with the applet.


16. How do you set security in applets?

using setSecurityManager() method


17. What is a layout manager and what are different types of layout managers available in java AWT?

 A layout manager is an object that is used to organize components in a container. The different layouts are available are FlowLayout, BorderLayout, CardLayout, GridLayout and GridBagLayout


18. What is JDBC?

JDBC is a set of Java API for executing SQL statements. This API consists of a set of classes and interfaces to enable programs to write pure Java Database applications.

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