Core Java Interview Questions
Java language was discovered by James Gosling of Sun Micro systems in 1991. Although C, C++ like programming languages were present in the market but due to fix platform constraint, web developers were unable to develop high end applications. Java has removed this constraint by being completely platform independent, secure, robust, dynamic, threaded & reusable programming language.
So if you are also studying java language and are going to appear for the java technical interview then do read some of these Core java interview questions to crack the interview easily.
1. What do you mean by JVM (Java Virtual Machine)? Explain its importance.
Java virtual machine helps in utilizing the same code in various forms by writing the code single time. Thus it saves the data space as well as increases the flexibility by using the same code everywhere during data execution. In order to execute this feature java virtual machine first compiles the source code i.e. dot java extension files into directory.
Then this source code file is coded into byte code and finally placed into dot class files into the directory. When this virtual machine starts the execution of byte code then java language gets interpreted as machine language in the directory.
2. What is garbage collection concept in Java?
Unlike C++ programming language, Java does not use the automatic response for assigning the memory location to data codes. Thus it avoids the problem of memory space corruption, data loss, as well as data garbage collection in the system. Instead Java uses a smart feature called garbage collector, which checks the free memory space into the system & overrides the delete operation thus avoiding the free data going into garbage box location & using the codes into other location.
3. Describe some core application of Java?
This is the usual question asked by the recruiter while during Core java interview questions round, as java has enabled its application from just a simple web based application to various high end industrial application. Java is currently being used in 3-D gaming application, flash video application, financial application in banks & other economical transactions, mobile, laptops, speakers & camera applications. You name any segment, and Java based application is there.
4. Is Java secure?
Java works on the abstraction and encapsulation concept which prohibits the access of data by third party or external user without getting permission from the content owner. This is the main reason, behind increasing use of java by the personal as well as corporate users for different web enabled applications. So yes Java is a highly secure language.
5. What is multithreading concept in Java?
Multithreading concept in Java works on principle of simultaneous running of different codes present into different classes or threads. Thus a single CPU can be used for executing different classes of data simultaneously as well as separately without disturbing the other threads working. Multiple tab opening in browsers is one such application of multithreading concept in Java.
6)What is difference between JDK,JRE and JVM?
JVM is an acronym for Java Virtual Machine, it is an abstract machine which provides the runtime environment in which java bytecode can be executed. JVMs are available for many hardware and software platforms (so JVM is plateform dependent).
JRE stands for Java Runtime Environment. It is the implementation of JVM and physically exists.
JDK is an acronym for Java Development Kit. It physically exists. It contains JRE + development tools.
7)How many types of memory areas are allocated by JVM?
· Class(Method) Area
· Program Counter Register
· Native Method Stack
8)What is JIT compiler?
Just-In-Time(JIT) compiler : It is used to improve the performance. JIT compiles parts of the byte code that have similar functionality at the same time, and hence reduces the amount of time needed for compilation. Here the term compiler refers to a translator from the instruction set of a Java virtual machine (JVM) to the instruction set of a specific CPU.
9)What is platform?
A platform is basically the hardware or software environment in which a program runs. There are two types of platforms software-based and hardware-based. Java provides software-based platform.
10)What is classloader?
The classloader is a subsystem of JVM that is used to load classes and interfaces. There are many types of classloaders e.g. Bootstrap classloader, Extension classloader, System classloader, Plugin classloader etc.
Core Java Interview Questions