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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