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JVM
This document provides an overview of the Java Virtual Machine (JVM) and how it executes Java code. It describes that the JVM converts Java bytecode into machine language and executes it, allowing Java programs to run on different platforms. It also outlines the key components of the JVM, including the class loader, execution engine, stack, method area, and garbage collected heap.
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JVM
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- 4. JAVA • Java programminglanguage was originally developed by Sun Microsystems. • Object Oriented : In Java, everything is an Object based. • Platform independent.
- 5. Virtual Machine • Avirtual machine (VM) is a software implementation of a machine (for example, a computer) that executes programs like a physical machine. • Virtual machines are separated into two major classifications: system virtual machine and process virtual machine.
- 6. JVM • A Javavirtual machine (JVM) is a process virtual machine that can execute java byte code. • JVM converts Java byte code into machine language and executes it. • JVM is platform dependent : JVMs are available for many hardware and software platforms. • JVM gives Java the flexibility of platform independence.
- 7. Diagram of JVM Javasource code Byte codeJava compiler Java Virtual Machine Java Interpreter Computer Operating System Byte code loaded into JVM
- 8. Block Diagram Class loadersub system Execution engine
- 9. Class loader • AllJava virtual machines include one class loader that is embedded in the virtual machine. • Class loader loads java classes into java virtual machine. • Class loader reads bytecode and creates the instance of java.lang.class.
- 10. Execution engine • Theexecution engine helps JVM to convert bytecode into machine code. • A mechanism responsible for executing the instructions contained in the methods of loaded classes.
- 11. Stack • Stack storesvarious method arguments and local variables of any method . • There are three registers that help in stack manipulation. – Vars register – Frame register – Optop register
- 12. Sections in stack •Local variable – This section contain all local variable being used by current method. • Execution environment – Execution section is used to maintain the operation of stack itself. • Operand stack – The operand stack is used as a work space by bytecode instruction.
- 13. Method Area • Thisis the area where byte code is placed. • The program counter points to the next instruction in the method area. • After the execution of an instruction , JVM set pc to next instruction.
- 14. Garbage Collected Heap •The object in java program are stored in Garbage collected heap. • Arrays in java program are objects, hence they also stored in heap. • Java does not have a free operator to free any previously allocated memory. • Java done this automatically by Garbage collection mechanism.
- 15. • JRE isan acronym for Java Runtime Environment. • Java Runtime Environment contains JVM, class libraries, and other supporting files. • It does not contain any development tools such as compiler, debugger, etc JRE
- 16. JDK • JDK isan acronym for Java Development Kit . It physically exists . It contains JRE + development tools.
- 17. JIT • Just-in-time Compiler-is the part of the Java Virtual Machine (JVM) that is used to speed up the execution time. • 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.
- 18. Is java acompiled or interpreted language ? • Java is a compiled language because the source code is converted into byte code. • Java is an interpreted language because the byte code is interpreted by a virtual machine.
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