What is language translator?

= Computers are digital devices. All types of commands, data and instructions required to be converted into machine code which is the combination of 0’s and 1’s. So, we give instructions to the computer in a language which is similar to English and easier for us to understand. The computer translates these instructions into the machine language with the help o language translators. Language translators are of three types.(i) Assembler: An assembler is software that converts programs written in assembly language to machine language.(ii) Interpreter: An interpreter is software that converts programs written in high level language to machine language code. It converts one instruction at a time.(iii) Compiler: A compiler is software that converts programs written in high level language to machine code in a single operation.

Difference between Compiler, Interpreter and Assembler

Lets get some of our concepts clear before to head on to programming in java.This and perhaps next few posts will help you clear some computer programming concepts.

Both compiler and interpreter convert human readable high level language like Java,C++ etc into machine language but there is difference in the way both function.So lets take a look to understand the differences.

Difference between Compiler and Interpreter

Compiler scans the entire program once and then converts it into machine language which can then be executed by computer's processor.In short compiler translates the entire program in one go and then executes it. Interpreter on the other hand first converts high level language into

an intermediate code and then executes it line by line. This intermediate code is executed by another program.

The execution of program is faster in compiler than interpreter as in interpreter code is executed line by line.

Compiler generates error report after translation of entire code whereas in case of interpreter once an error is encountered it is notified and no further code is scanned.

Example Python is an interpreted language whereas C,C++ are compiled languages.Java however uses both compiler and interpreter.We will look into how this exactly works in case of java in next post.

Diagrammatic representation-

What is Assembler? Assembler is used for converting the code of low level language (assembly language) into machine level language.If you have worked on microprocessors like 8085 and 8086 the module which converts assembly language into machine language is nothing but Assembler.

Java - Compiled or interpreted?

As our basics are now clear lets get on to Java. Well you must have heard that Java is both compiled and interpreted language. When it comes to the question - How Java works? It goes something like below -

When you run javac HelloWorld.java java compiler is invoked which converts human readable code(Contents of .java file) to java byte codes(intermediate form). This bytecodes are stored in a special file(called Class file) with .class extension.

Finally when you run java HelloWorld java interpreter is invoked which reads these bytecodes line by line, convert it into machine language and execute it.

This is why Java is called as both compiled as well as interpreted language. But this is not all. There is another concept called - Just-in-time compilation

JIT(Just-in-time compilation)You can read the wiki page for complete details but here I am only going to provide relevant points from Java perspective.

JIT as the name suggests does just in time or on the fly compilation of java byte codes to native machine language that can be directly executed by the processor.

JIT compiler runs only after the program(JVM) has started. so it has access to dynamic runtime information whereas a standard compiler doesn't and can make better optimizations like inlining functions that are used frequently.

But question may arise - Addition time is spent every time to compile the code?

Yes it is true if we use pure JIT then additional time is spent compiling every time code is run and hence a new technique was introduced - HotSpot Compiling. In this

JVM maintains a count of number of time a module/routine is executed. When program/JVM first starts it goes through normal compilation to bytecodes followed by interpretation.

But if the count of execution exceeds a limit the corresponding byte codes are compiled to machine code by JIT and are directly executed thereafter.

The advantage is that there is no initial delay due to the compiling.

Above picture best represents the overview.

Java compiler (javac) converts Java code to byte code and then Java interpreter (java) interprets bytecodes line by line, converts it into native code and executes it.

However if a "hot spot" is encountered - typically a piece of code or method that is getting executed very frequently then JIT compiler comes up. Compiles the byte code to native code with optimizations (as JIT has runtime information) and thereafter that piece of code is never interpreted - the native code generated by JIT is directly executed.

Yes this will have an additional overhead in terms of time and memory footprint as JIT performs optimizations and compilation into native code on the fly (as your application is running) but subsequent calls to that part of code are efficient and fast.

Assembler, Compiler, Interpreter, Linker, Loader

Assembler: A computer will not understand any program written in a language, other than its machine language. The programs written in other languages must be translated into the machine language. Such translation is performed with the help of software. A program which translates an assembly language program into a machine language program is called an assembler. If an assembler which runs on a computer and produces the machine codes for the same computer

then it is called self assembler or resident assembler. If an assembler that runs on a computer and produces the machine codes for other computer then it is called Cross Assembler.

Assemblers are further divided into two types: One Pass Assembler and Two Pass Assembler. One pass assembler is the assembler which assigns the memory addresses to the variables and translates the source code into machine code in the first pass simultaneously. A Two Pass Assembler is the assembler which reads the source code twice. In the first pass, it reads all the variables and assigns them memory addresses. In the second pass, it reads the source code and translates the code into object code.

Compiler: It is a program which translates a high level language program into a machine language program. A compiler is more intelligent than an assembler. It checks all kinds of limits, ranges, errors etc. But its program run time is more and occupies a larger part of the memory. It has slow speed. Because a compiler goes through the entire program and then translates the entire program into machine codes. If a compiler runs on a computer and produces the machine codes for the same computer then it is known as a self compiler or resident compiler. On the other hand, if a compiler runs on a computer and produces the machine codes for other computer then it is known as a cross compiler.

Interpreter: An interpreter is a program which translates statements of a program into machine code. It translates only one statement of the program at a time. It reads only one statement of program, translates it and executes it. Then it reads the next statement of the program again translates it and executes it. In this way it proceeds further till all the statements are translated and executed. On the other hand, a compiler goes through the entire program and then translates the entire program into machine codes. A compiler is 5 to 25 times faster than an interpreter.

By the compiler, the machine codes are saved permanently for future reference. On the other hand, the machine codes produced by interpreter are not saved. An interpreter is a small program as compared to compiler. It occupies less memory space, so it can be used in a smaller system which has limited memory space.

Linker: In high level languages, some built in header files or libraries are stored. These libraries are predefined and these contain basic functions which are essential for executing the program. These functions are linked to the libraries by a program called Linker. If linker does not find a library of a function then it informs to compiler and then compiler generates an error. The compiler automatically invokes the linker as the last step in compiling a program.

Not built in libraries, it also links the user defined functions to the user defined libraries. Usually a longer program is divided into smaller subprograms called modules. And these modules must be combined to execute the program. The process of combining the modules is done by the linker.

Related Links

Java theory and practice: Dynamic compilation and performance measurement What does a just-in-time (JIT) compiler do?(SO)

Static Keyword in Java Mounting Solaris NFS Share on Linux(Ubuntu) Difference between data encapsulation and data abstraction in java. Building Java projects with Maven.

- See more at: http://opensourceforgeeks.blogspot.in/2013/03/difference-between-compiler-interpreter.html#sthash.bYLQNezV.dpuf

Compiler Interpreter Assembler Debugger

What is an Compiler?In general, compiler is a computer program that reads a program written in one language, which is called the source language, and translates it in to another language, which is called the target language. Traditionally, source language is a high level language

such as C++ and target language is a low level language such as Assembly language. However, there are compilers that can convert a source program written in Assembly language and convert it to machine code or object code. Assemblers are such tools. On the other hand, Interpreters are tools that execute instructions written in some programming language. Interpreter can either directly execute high level source code or translate them to intermediate code and then interpret it or execute precompiled code.

What is an Assembler?Assembler is software or a tool that translates Assembly language to machine code. So, an assembler is a type of a compiler and the source code is written in Assembly language. Assembly is a human readable language but it typically has a one to one relationship with the corresponding machine code. Therefore an assembler is said to perform isomorphic (one to one mapping) translation. Advanced assemblers provide additional features that support program development and debugging processes. For example, the type of assemblers called macro assemblers provides a macro facility.

What is an Interpreter?An interpreter is a computer program or a tool that executes programming instructions. An interpreter may either execute the source code directly or converts the source to an intermediate code and execute it directly or execute precompiled code produced by a compiler (some interpreter systems include a compiler for this task). Languages like Perl, Python, MATLAB and Ruby are examples of programming languages that use an intermediate code. UCSD Pascal interprets a precompiled code. Languages like Java, BASIC and Samltalk first compile the source to an intermediate code called bytecode and then interpret it.

What is a Debugger?Debugger is a computer program that is used to find bugs/errors in other programs. Debugger allows executing a program and inspecting each step in the program execution. It also allows stopping the execution of the program at some point and changing some variable values and then continuing the execution. All of these capabilities are provided to help the programmer to make sure that her program is behaving correctly and to help in

identifying bugs in the code. Most of the debuggers provide the ability to execute a program step by step (also called single stepping), pausing to examine the current state of the program by providing a breakpoint and tracking variable values. Some advanced debuggers allow the programmer to skip a location that causes a crash or a logical error in the code and continue execution from a different location. Some of the popular debuggers are GNU Debugger (GDB), Microsoft Visual Studio Debugger, etc.

Compiler  V/s Interpreter V/s Assembler

Compiler1.Compiler translates a high level language program into machine level language.2.translates each high level language instruction into a set of machine level instructions3.one to many correspondence.4.Examples are C, COBOL, Java, etc. .

Interpreter1.Compiler translates a high level language program into machine level language.2.It takes one statement of a high level language program, translates it into machine language instructions and immediately executes it.3.a one to one relationship with the corresponding machine code4.Languages like Java, BASIC and Samlltalk first compile the source to an intermediate code called bytecode and then interpret it.

Assembler1.Assembler translates a assembly language program into machine level language.2.It takes one statement of a assembly language program, translates it into machine language instructions and immediately executes it.3.typically has a one to one relationship with the corresponding machine code