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JVM

Disclaimer: This presentation is prepared by trainees of baabtra as a part of mentoring program. This is not official document of baabtra –Mentoring PartnerBaabtra-Mentoring Partner is the mentoring division of baabte System Technologies Pvt . Ltd

Java Virtual machine (JVM)

• A process virtual machine that can execute Java bytecode.

• *.java files are compiled to obtain *.class files that contain the bytecodes understandable by the JVM.

• JVM interprets the bytecodes during execution of Java program.

• Byte code is the entity that allows Java to be a "portable language" (write once, run anywhere).

• Indeed there are specific implementations of the JVM for different systems (Windows, Linux, MacOS).

• The aim is that with the same bytecodes they all give the same results.

• JVM is platform dependent • Java is platform independent

JVM

Implementation of JVM

Just In Time(JIT)• JIT are advanced part of Java Virtual machine

• It optimize byte code to machine instruction conversion by compiling similar byte codes at same time

• thus reducing overall execution time.

• JIT performs several optimizations such as in-lining function.

• JIT compiler improve perfomance

Different JVM layers and interaction

Java Runtime Environment (JRE)

• Provides the libraries, the Java Virtual Machine, and other components to run applets and applications written in the Java programming language.

• The JRE does not contain tools and utilities such as compilers or debuggers for developing applets and applications.

Java Development Kit (JDK)

• Most used by developers to develop java based applications.

• The JDK is a superset of the JRE, and contains everything that is in the JRE, plus tools such as the compilers and debuggers necessary for developing applets and applications.

IsJavaCompiled or interpretedprogramming language?

Java is both compiled and interpreted language.

Java compiles using javac and JIT, and interprets using Java virtual machine.

Java

from writingto execution:

Programmer write source code and store that into a .java file.

Note: Name of your Java source file must be same with the public class declared inside that file, for example if there is public class called Order inside Java file, then it name must be Order.java

1

javac compiles .java fie and creates class files, which contains byte code.

2

JVM executes these class files and gathers statistics of execution run.

These statics are used to determine hot spot i.e. part of your code which executes 90% of time.

3

When JVM has enough data to make decision,

JIT compiles frequently used byte codes into native code, which is then directly executed by platform.

This is how JIT provides performance boost to Java application.

4

thankyou

RAZI KALLAYI

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