ClassLoading - Revision history

Suhridk at 18:22, 23 November 2012

2012-11-23T18:22:28Z

2012-11-23T18:20:38Z

2012-11-23T18:16:10Z

2012-11-23T18:14:36Z

2012-11-23T18:05:41Z

2012-11-23T18:00:39Z

2012-11-23T17:48:53Z

2012-11-23T17:41:35Z

2012-11-23T17:36:07Z

Created page with "= Binary Class = * The binary class format is defined in the JVM spec. *"

New page

= Binary Class =

* The binary class format is defined in the JVM spec.
*

← Older revision		Revision as of 18:22, 23 November 2012
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	* Example: Each J2EE application loaded by the framework needs to have a separate class loader to prevent classes in one application from interfering with other applications.		* Example: Each J2EE application loaded by the framework needs to have a separate class loader to prevent classes in one application from interfering with other applications.
	* Through the use of class loaders, Java applications are able to work with multiple versions of classes that would otherwise cause conflicts.		* Through the use of class loaders, Java applications are able to work with multiple versions of classes that would otherwise cause conflicts.
		+	* Potential for confusion also exists because class is identified through a combination of name and its loading class loader. So e.g. when same code is moved between class loaders it will be treated differently.

← Older revision		Revision as of 18:20, 23 November 2012
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	* Each class loader keeps a reference to custom class loaders.		* Each class loader keeps a reference to custom class loaders.
	* Example: Each J2EE application loaded by the framework needs to have a separate class loader to prevent classes in one application from interfering with other applications.		* Example: Each J2EE application loaded by the framework needs to have a separate class loader to prevent classes in one application from interfering with other applications.
		+	* Through the use of class loaders, Java applications are able to work with multiple versions of classes that would otherwise cause conflicts.

@@ Line 28: / Line 28: @@
 * Apps can also provide custom class loaders.
 * Each class loader keeps a reference to custom class loaders.
+* Example: Each J2EE application loaded by the framework needs to have a separate class loader to prevent classes in one application from interfering with other applications.

← Older revision		Revision as of 18:14, 23 November 2012
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	** verifying the sequence of bytecode operations		** verifying the sequence of bytecode operations
	** finally constructing a java.lang.Class instance to represent the new class		** finally constructing a java.lang.Class instance to represent the new class
		+
		+	= Class Loaders =
		+
		+	* Class loaders control class loading in a JVM.
		+	* The bootstrap class loader is resp. for loading the basic Java library classes. Loads classes found on the boot class path. Since this is trusted, skips the validation process.
		+	* Extension class loader for Java extension APIs.
		+	* System class loader for classes from the general class path.
		+	* Apps can also provide custom class loaders.
		+	* Each class loader keeps a reference to custom class loaders.
		+	*

← Older revision		Revision as of 18:05, 23 November 2012
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	* E.g. Apps can be written to use interfaces with the actual implementation loaded at runtime.		* E.g. Apps can be written to use interfaces with the actual implementation loaded at runtime.
	* Basic principle is that classes are loaded when needed.		* Basic principle is that classes are loaded when needed.
		+	* A lot happens inside the JVM when a class is loaded and initialized :
		+	** decoding the binary class format
		+	** checking compatibility with other classes
		+	** verifying the sequence of bytecode operations
		+	** finally constructing a java.lang.Class instance to represent the new class

← Older revision		Revision as of 18:00, 23 November 2012
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	* The JVM uses a stack architecture with instruction operands being loaded onto an internal stack.		* The JVM uses a stack architecture with instruction operands being loaded onto an internal stack.
	* Early JVM's were interpreters - Next gen JVM's added JIT to compile bytecode to native code.		* Early JVM's were interpreters - Next gen JVM's added JIT to compile bytecode to native code.
		+
		+	= Loading the classes =
		+
		+	* C/C++ require a linker to merge all compiled code from various source files, alongwith code from libraries to form a single executable.
		+	* In case of Java, it's different. Linking compiled classes is performed by the JVM when it loads the classes into memory.
		+	* E.g. Apps can be written to use interfaces with the actual implementation loaded at runtime.
		+	* Basic principle is that classes are loaded when needed.

← Older revision		Revision as of 17:48, 23 November 2012
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	* The binary class format is defined in the JVM spec. So compatible class files can be produced from any language definition.		* The binary class format is defined in the JVM spec. So compatible class files can be produced from any language definition.
−	*	+	* Every binary class starts with the "cafe babe" signature.
		+	* Class format version numbers - minor and major.
		+	* Bytecode is machine code for the JVM.
		+	* The JVM uses a stack architecture with instruction operands being loaded onto an internal stack.
		+	* Early JVM's were interpreters - Next gen JVM's added JIT to compile bytecode to native code.

@@ Line 1: / Line 1: @@
 = Binary Class =
-* The binary class format is defined in the JVM spec.
+* The binary class format is defined in the JVM spec. So compatible class files can be produced from any language definition.
+*