Class File Inwards Coffee - Things To Know For Programmer In Addition To Developer
.class file inwards Java is centre of achieving platform independence which is cardinal characteristic of Java. class files are compiled cast of whatever Java computer program written inwards byte codes. Since Java computer program executes within JVM, these instructions are read yesteryear JVM in addition to than translated into machine code for underlying platform. effectively y'all tin move run class file on whatever platform if y'all convey a corresponding JVM supported for that platform. Java compilers are responsible for generating .class file in addition to they follow class file format specified yesteryear Lord's Day in addition to its unlike based on unlike Java version. This article is non a detailed ane focused on class file format instead it contains basic information nearly course of pedagogy files in addition to intended to plow over an thought nearly what is a class file inwards Java in addition to what are roughly of import points related to course of pedagogy files.
This Java article is inwards continuation of my serial of 10 points of interface inwards Java in addition to 10 Object oriented pattern principles for Java programmer. If y'all haven’t got gamble to read them y'all may notice them useful.
What is class file inwards Java
In full general every course of pedagogy file inwards coffee contains Definition of a unmarried course of pedagogy or interface inwards stream of 8 flake bytes. Every .class file follows a predefined course of pedagogy file format, failing which .class file volition locomote deemed invalid in addition to non run on whatever JVM or JRE. course of pedagogy file is generated yesteryear Java compilers in addition to executed yesteryear Java virtual machine in addition to its byte code is verified during course of pedagogy loading process, which address possibility of altering .class file externally. One of the argue Java is considered relatively condom in addition to secure linguistic communication is its mightiness to verify class file byte codes earlier executing it. class file contains 10 basic sections which specifies all information in addition to meta information similar magic numbers, major in addition to pocket-sized fry version of course of pedagogy file etc. Read officialVM spec for course of pedagogy file format for to a greater extent than details on how a .class file looks like.Important points nearly course of pedagogy file inwards Java
1. class file inwards coffee is generated when y'all compile .java file using whatever Java compiler similar Sun's javac which comes along JDK installation in addition to tin move locomote works life inwards JAVA_HOME/bin directory.
2. course of pedagogy file contains byte codes. byte codes are particular platform independent pedagogy for Java virtual machine. bytecode is non a machine linguistic communication in addition to mere pedagogy to JVM. since every machine or processor e.g. INTEL or AMD processor may convey unlike pedagogy for doing same thing, its left on JVM to interpret bytecode into machine pedagogy in addition to yesteryear this agency coffee achieves platform independence.
3. class file of inner course of pedagogy contains $ inwards at that spot name. So if a Java root file contains 2 classes, ane of them is inner course of pedagogy than coffee compiler volition generate 2 course of pedagogy file. separate course of pedagogy file for transcend marking in addition to inner class. y'all tin move distinguish them yesteryear looking at at that spot name. Suppose y'all convey top marking class every bit "Hello" in addition to inner course of pedagogy every bit "GoodBye" in addition to hence coffee compiler volition generate 2 course of pedagogy file:
Hello.class
Hello$GoodBye.class
Hello$GoodBye.class
Hello$GoodBye.class is a course of pedagogy file for inner class. whose advert is inwards format of top-class$inner-class.
4. You tin move await bytecode of class file using javap command. javap command tin move besides display method in addition to champaign information from .class file. run across my postal service how to decompile .class file inwards Java for to a greater extent than details.
5. class file format is dependent area to modify in addition to its changed to back upward novel characteristic introduced inwards Java 1.5. In full general every coffee compiler in addition to JRE comes alongside supported version of .class file format in addition to y'all tin move non run a .class file which is inwards higher version of those supported yesteryear JRE. this oft final result inwards java.lang.UnsupportedClassVersion. class file has 2 version major in addition to pocket-sized fry which is included within class file. See my postal service Bad version lay out inwards .class file for to a greater extent than details.
6. .class file inwards coffee is identified yesteryear a magic lay out inwards header which is a four byte CA FE BA BE ( inwards hex). which is the kickoff chemical component inwards .class file, followed yesteryear major in addition to pocket-sized fry versions of class file
7. .class file allows Java Virtual machine to implement security. Since lay out of pedagogy class file contains are limited. besides if roughly ane tempers .class file externally it may non run on unlike browsers in addition to JRE.
8. Java course of pedagogy file tin move locomote divided into 10 basic sections e.g.
Magic Number : 0xCAFEBABE
Major in addition to Minor course of pedagogy version or .class file
Constant puddle - constants for this class
Access modifiers - to signal whether course of pedagogy is static or abstract
This course of pedagogy - advert of this class
Super course of pedagogy - advert of super class
Interfaces -
Fields
Methods
Attributes
9. Top marking .class file advert is same every bit advert of coffee root file e.g. Hello.java volition create Hello.class
10. You tin move persuasion class file inwards whatever hex editor or whatever byte code viewer plug-in inwards Eclipse.
That's all on what is class file in addition to basics of .class file. As I said this is non a detailed article on .class file format rather this is the bare minimum information regarding .class file an average coffee programmer should locomote familiar with. I highly recommend to read to a greater extent than nearly .class file format if y'all are interested simply it depends upon your sense marking in addition to beginners may non notice the class file format slow to understand.
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