VS.
Abd El-Rahman Hosny Alaa Attyea M.
Agenda- Previous State of Affairs.- Introduction to Java• Compilers vs. Interpreters.• Platform-Dependency.• Hybrid Compiler-Interpreter.• Java Components (JDK).• JIT Solution.
- The .NET Solution• CLR, CTS and CLS.• Base Class Library.• .NET Sons.
- What’s Next?!
Punched Cards
- Piece of paper, that contains digital information.- Information is represented by the presence or absence of holes
in predefined positions.
Previous State of Affairs ..
Previous State of Affairs .. Assembly Programming
- More readable for programmers.- Consists of machine instructions.- Each computer architecture has its own assembly commands.- Reduced Instruction Set Computing (RISC).- Complex Instruction Set Computing (CISC).- Using assembler: assembly code => executable machine code.- However, still a low-level programming language.
- High-level assembler for assembly languages that have some high-level programming features.
Previous State of Affairs ..
Previous State of Affairs .. C/Windows API
- To develop software for Windows operating systems, we use C programming language with the Windows application programming interface (API).
- Large number of applications already created with this approach.
- However … Manual memory management.Ugly pointer arithmetic.Spaghetti code (thousands of functions & data types).
Previous State of Affairs .. C++/MFC
- Object-oriented layer on top of C.- Benefits of OOP (Encapsulation, Inheritance, Polymorphism)- Microsoft Foundation Classes (MFC) are set of C++ classes
that facilitate building Windows applications.- MFC hade the underlying Windows API and provide classes,
macros and code generation tools (wizards).
- However …Backward compatibility with C makes it prone to the same problems (memory management, pointers, constructs).
Previous State of Affairs .. Visual Basic 6.0
- Programmer is now able to build complex user interfaces and code libraries.
- Can access databases easily.- Hide Windows API by using code wizards, VB data types,
classes and VB-specific functions.
- However …Not fully OO (rather it’s object-based).No is-a relationship (No inheritance).No Multi-threaded applications (actually we can use lower level APIs.
Previous State of Affairs .. COM
- Stands for Component Object Model.- Microsoft’s previous application development framework.
- “If you build your types in accordance with the rules of COM, you end up with a block of reusable binary code”.
- Language-Independent.- ATL ( Active Template Library) provides a set of C++ classes,
templates & macros.
- However … Complex Data Type representation
The Move ...
What is a program & how it runs ?!
Source code and native bits:
- Source code a series of related commands of specific programming languages.
- Actually source code is not what runs on our machines.
- Machines knows only it’s native language (0s&1s).
- Source code must be translated in some way to the machine native language.
Compilers Vs interpreters :
- Compilers and interpreters and some software that acts as a translator between you (high level language) and the machine (low level language).
- Actually compilers and interpreters are totally different in the ways how they treat your code.
- Let’s take a look about how they are working.
What is interpreter ?!
- Interpreters doesn’t behave like compilers.
- It do not translate any programming commands, it takes the code and executes it line by line.
- Examples for interpreted languages PHP, haskell, aslo shell command in linux are interpreted.
Platform dependent problem:
- As there are different computer architectures there must exist different compilers to translate the code.
- Here w have the platform dependent problem.
- However … There another solution for that problem called, hybrid compiler-interpreter.
- In this case first there will be intermediate code, which will run over the interpreter and we’ll get the result.
Hybrid Compiler-interpreter:
Java solution and the power of Java:
- Java has the same solution about that issue.
- After we have written our source code, when we compile it using the javac command, it will generate the intermediate code or what is called byte code.
- This will be at the form of (.class) file.
- JRE can be responsible for running and executing the .class file over the machine.
Java components:
- The first step to write a java program and run it is to set up something called JDK (Java Development Kit).
- This includes three main component for java• JRE (JVM is a part of it).• Java compiler (javac).• Java debugger.
- With the help of these component you can run your code wherever and whatever the architecture or platform of your machine.
- After the programmer have written the source code, he’ll use the javac to compile the (.java file)
- Then the javac will create an intermediate code that is known as (.class file) or byte code.
- This byte code can run over any JVM regardless of the machine architecture or platform.
How the Java Program Runs ?
- It is a set of dynamically loadable libraries that java application uses at run time.
Java Class Library
JCL serves three purposes within the Java Platform:
- They provide the programmer a well-known set of useful facilities.
- Provides an abstract interface to tasks that would normally depend heavily on the hardware and operating system, such as network access and file access.
- Some underlying platforms may not support all of the features a Java application expects. In these cases, the library implementation can either emulate those features or provide a consistent way to check for the presence of a specific feature.
JIT:
- Java uses different ways to generate machine the machine code.
- There is a way to produce efficient machine code called JIT (Just In Time compilation).
- JIT compilers promise to improve the performance of Java applications.
- Rather than letting the JVM run bytecode, a JIT compiler translates code into the host machine’s native language.
- Thus, applications get the performance enhancement of compiled code while maintaining Java’s portability.
Java Garbage collector:
- Objects are created in the heap.
- Garbage collector looks for those objects that are not referencing and memory location and reclaim the heap from those objects.
- Garbage Collection in Java is carried by a daemon thread called Garbage Collector.
- Interoperability with existing source code.
- Support for many programming language.
- Common run-time engine shared by all .NET-aware languages.
- Complete and total language integration.- Comprehensive base class libraries.- No COM.- Simplified deployment model.
The .NET Solution
.NET Building Blocks
CLRCommon Language
Runtime
CTSCommon Type System
CLSCommon Language
Specification
CTS (Common Type System)
- CTS Specification fully describes all possible data types and programming constructs supported by the run-time.
- CTS specifies how these entities can interact with each other and how they are represented in the .NET metadata format.
- Some .NET language might not support every feature defined by the CTS.
CLS (Common Language Specification)
- CLS is a set of rules that describes, in detail, the minimal and complete set of features a given .NET-aware compiler must support to produce code that can be hosted by the CLR, while at the same time can be accessed in a uniform manner by all languages that the .NET platform support.
- CLS is a subset of the full functionality of CTS.
CLR (Common Language Runtime)
- The CLR locate, load and manage .NET types on your behalf. - Memory Management (Garbage Collector). - Application Hosting.- Handling Threads.- Security Checks.
CLR (Common Language Runtime) .. cont.
- When an assembly is referenced for use, mscore.dll is loaded automatically, which loads the required assembly in turn.(MS Common Object Runtime Execution Engine).
- Creating the required custom types.- The key assembly is the mscore.dll, which contains a large number of types, that
encapsulate a wide variety of common programming tasks as well as the core data types used by all .NET languages.
- In addition to CLR and CTS/CLS specifications, the .NET platform provides a base class library that is available to all .NET programming languages
Base Class Library
- CIL: the same as Java bytecode, it’ not compiled into platform specific instructions until absolutely necessary.
- You can view the CIL code of any assembly using either:ildasm.exe or using Reflector.
- Metadatadescribes, in detail, the characteristics of every type within the binary.
- Manifest:The current version of the assembly.Culture information (localizing string & image resources).List of externally referenced assemblies that are required for the proper execution of the program.
Single-File assembly vs. Multi-File assembly.
- Applications running in a managed environment tend to require more system resources than similar applications that access machine resources more directly
- Managed byte code can often be easier to reverse-engineer than native code.
- The .NET Framework currently does not provide support for calling Streaming SIMD Extensions (SSE) via managed code.
- While the standards that make up .NET are inherently cross-platform, Microsoft's full implementation of .NET is only supported on Windows.
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