QA's approach 2 Java - Understanding JVM, JRE, JDK

-





JVM:

It interprets byte code into machine code depending upon thee underlying OS and hardware combination
It uses the class libraries or packages like util, math, awt, lang, swing, etc.., and other supporting files provide in JRE

The JVM is responsible for the following:

• Loading, verifying, and executing the byte code

• Providing a runtime environment for execution of byte code

• Memory management and garbage collection

jvm consists of classloader, memory area, execution engine


Class Area/Method Area:
This is the region where the Execution class gets loaded in the order they are defined.
Static Variables gets initialized with default values.

Heap Area: 

This is the region of memory where objects are stored & memory is allocated for non-static variables.

Stack Area: 

Order considered for execution of blocks & methods in stack frame as follows:
Static blocks, Static main method, Static User defined methods, Non Static blocks, Non static methods will be allocated with individual memory stacks frames & gets executed one after the other in the above defined order.

The JVM stores local variables and intermediate results of execution of methods in the stack.


JRE

JRE =JVM+Java class libraries/packages+Run time libraries

Its a Run time environment which implements Java virtual machine , and provides all class libraries & other facilities to execute Java program.


Class Loader
Virtual machine instructions are stored in class files. Each class file contains the instructions for a single class or interface.

When executing a Java program, at least three class loaders are involved.

The bootstrap class loader:
loads Java library classes (typically from the JAR file jre/lib/rt.jar). It is a part of the virtual machine.
Run time libraries

The extension class loader:
loads “standard extensions” from the jre/lib/ext directory.
Predefined Java packages like lang, util, math, etc.

The system class loader:
loads the application classes. It locates classes in the directories and JAR files on the class path.
loads business logic class files from the defined class path.

JDK:


Comments

Post a Comment

Popular posts from this blog

QA's approach 2 Java - Understanding Static context

-
Image
            Static Members Flow Class members In java application we are defining objects for communication.Every Object is represented as a model(class). Hence, java application is the combination of classes. And every class in java application is allowed to define following members. 1) static members 2) non-static members Static members flow using JVM architecture : Java class supports definition of 4 static members. 1) static main method 2) static block 3) static variable 4) static method Static main method Example class Demo { //empty..... } How to Compile & Execute a simple Java program? 1) Save the program in "d-drive" with name Demo.java 2) Open command prompt, navigate to the path where the java program is stored 3) Compilation: cmd/> javac Demo.java Demo.class file will be generated. 4) Execution:  cmd/>java Demo Error : main method not found... main method : 1) It is static method, hence...
Read more

Selenium 4 absolute beginners - How to create Batch execution file

-
Sample Batch Execution file @echo off :: Delete the existing log file ERASE C:\Softwares\Workspace\ProductNameAutomation\build.log :: Create a new Empty log file  echo.>C:\Softwares\Workspace\ProductNameAutomation\build.log :: Setting project Home Path SET PROJECT_HOME=C:\Softwares\Workspace\ProductNameAutomation cd %PROJECT_HOME% echo CURRENTLY WORKING ON DIRECTORY %PROJECT_HOME% PATH echo Setting configurations SET M2_HOME=C:\Softwares\Workspace\apache-maven-3.5.4 SET M2=%M2_Home%\bin SET path=%M2_Home%\bin ::SET Java_Home="C:\Program Files (x86)\Java\jdk1.8.0_181" ::Start the test case echo test execution in progress call mvn -f C:\Softwares\Workspace\ProductNameAutomation\pom.xml clean install compile test -X -l C:\Softwares\Workspace\ProductNameAutomation\build.log echo test execution in completed :: Generating report based on above ran test cases echo Report generation is in progress call mvn surefire-report:rep...
Read more

Technologies - Log4J - Create Log4j Configuration File - Where ? How ? What ?

-
  Typical Steps involved in Creating Log4j Configuration file Configure the root logger - What to Log - info/debug/error/fatal messages Configure individual loggers (if needed). Specify appenders -- Where to Log -- in File/Console, etc Specify message layout/Pattern -- How to Log - format to log the message Configuring a Layout PatternLayout lets you determine how data is extracted from log events and formatted for output based on a conversion pattern. Conversion patterns act as placeholders for data that appears in each log event.  For example, let’s break down a PatternLayout commonly used in Log4j: <PatternLayout pattern="%d{HH:mm:ss.SSS} [%t] %-5level %logger{36} - %msg%n"/> %d{HH:mm:ss.SSS} formats the date in terms of hours, minutes, seconds, and milliseconds. %t displays the Logger’s current thread. %level displays the severity of the log event. %logger displays the name of the Logger. %m displays the event’s message. Finally, %n adds a new line for the next e...
Read more