Java Memory Descreption

Java Memory Descreption

• 1.
  Topics we shouldCover ● JDK VS JRE vs JVM ● RunTime Data Areas ● Object memory representation ● Object array memory
• 2.
  Topics we shouldCover ● JDK VS JRE vs JVM ● RunTime Data Areas ● Object memory representation ● Object array memory
• 3.
  JDK VS JREvs JVM Similarity JVM, JRE and JDK are platform dependent because configuration of each OS differs. But, Java is platform independent. JVM (Java Virtual Machine) ● ~ is an abstract machine ● ~ is a specification that provides runtime environment in which java bytecode can be executed. ● ~ are available for many hardware and software platforms.
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  JDK VS JREvs JVM The JVM performs following main tasks: ● Loads code ● Verifies code ● Executes code ● Provides runtime environment
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  JDK VS JREvs JVM JRE ● ~is an acronym for Java Runtime Environment. ● ~ is used to provide runtime environment. ● ~ is the implementation of JVM. ● ~ physically exists. ● ~ contains set of libraries + other files that JVM uses at runtime. ● ~ released and maintained by Sun Micro
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  JDK VS JREvs JVM JDK ● ~is an acronym for Java Development Kit. ● ~physically exists. ● ~ It includes: + Java Runtime Environment (JRE), + an interpreter/loader (Java), + a compiler (javac), + an archiver (jar), + a documentation generator (Javadoc) and other tools needed in Java development.
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  JDK VS JREvs JVM
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  In Depth JRE(How does JRE works) JRE consists of the following components: ● Deployment technologies: ○ deployment, Java Web Start and Java Plug-in. ● User interface toolkits: ○ AWT, Swing, Java 2D, Accessibility, Image I/O, Print Service and more. ● Integration libraries: ○ JDBC, IDL, JNDI, RMI etc ● Other base libraries: ○ I/O, i18, Beans, Math, Networking etc.
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  In Depth JRE(How does JRE works) ● Lang and util base libraries: ○ lang and util, management, versioning, zip, instrument, reflection, Collections, Concurrency Utilities, Java Archive (JAR), Logging, Preferences API, Ref Objects and Regular Expressions. ● Java Virtual Machine (JVM): ○ including Java HotSpot Client and Server Virtual Machines.
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  JVM Run-Time DataAreas
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  JVM Run-Time DataAreas Individual Thread : ● Not Shared ● created when a new thread is created ● include program counter register, JVM Stack, and Native Method Stack ○ is used to control each execution of each thread ○ contains frames, throws StackOverFlow error when stack get full ○ is used to support native methods
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  JVM Run-Time DataAreas Frame: a frame is pushed to the stack when a method is invoked
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  JVM Run-Time DataAreas Shared by All Threads All threads share Heap and Method Area ● Heap: ○ most frequently deal with area. ○ It stores arrays and objects, created when JVM starts up. ○ Garbage Collection works in this area. ● Method Area: ○ stores run-time constant pool, field and method data, methods and constructors code。　 ●
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  JVM Run-Time DataAreas Shared by All Threads All threads share Heap and Method Area ● Runtime Constant Pool: ○ ~is a per-class or per-interface run-time representation of the constant_pool table in a class file. ○ contains several kinds of constants, ranging from numeric literals known at compile-time to method and field references that must be resolved at run-time.
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  Heap Details
• 20.
  java -Xms=1M -XmX=2M"Class Name" java -Xss=512M "Class Name"