What is a Programing Language? Programming Languages • A formal language designed to communicate instructions to a machine • Mechanical, Electrical, combo • Typically, a programming language is developed to make programming easier • Logical, imperative, functional • Important bits: Syntax and Semantics • Syntax: How to write it! • Semantics: What does it mean? Programming Languages • Why have a programming language? – Because computers are, in the end, nothing more than a series of on/off switches. Thus, the only real way to would in binary to represent the various on/off states. Computers still use this language and only this language. It is called Machine Code • So what would that be an issue? – Here is basic program in binary 11000111 00111100 00101010 00111100 00101010 00101011 00101010 01011100 00111100 00101000 01011100 00101010 00101011 00101010 01011100 00111100 00101000 01011100 00101010 00101011 00101010 01011100 00111100 00101000 01011100 00101010 00101011 00101010 01011100 00111100 00101000 01011100 00101010 00101011 00101010 01011100 00111100 00101000 01011100 00101010 00101011 00101010 01011100 00111100 00101000 01011100 00101010 00101011 00101010 01011100 00111100 00101000 01011100 00101010 00101011 00101010 01011100 00111100 00101000 01011100 00101010 00101011 00101010 01011100 00111100 00101000 01011100 00101010 00101011 00101010 01011100 00111100 00101000 01011100 00101010 00101011 00101010 01011100 00111100 00101000 01011100 00101010 00101011 00101010 01011100 00111100 00101000 01011100 00101010 00101011 00101010 01011100 00111100 00101000 01011100 00101010 00101011 00101010 00000000 00000000 00000001 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 01100100 01001000 01100101 01101100 01101100 01101111 00101100 00100000 01010111 01101111 01110010 01101100 01100100 00100001 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000 • Yeah, that looks… painful. So what did they do about it? – Assembly Language! Programming Languages • What is assembly language? – Machine code is the primordial computing language (a lot like baby babble or monkey chatter) and assembly language is considered a low-level language (think cave man grunting). Here is the pervious program in assembly language – A_CR = $0D ; BSOUT = $FFD2 ; LDX #$00 ; LOOP LDA MSG,X ; BEQ LOOPEND ; JSR BSOUT ; INX BNE LOOP ; LOOPEND RTS ; MSG .BYT 'Hello, world!',A_CR,$00 • That doesn’t look much better… – Its not but that is what most of the computer hardware today is capable of reading so we still use it. Granted it doesn’t really solve the issue that programming is assembly language is both cruel and unusual • Ok, so what did they do about that issue? – If Assembly language is a low-level language, then we need to level up! Programming Languages • Level up? What does that mean? – It means that we will need a High-level Language. Remember FORTRAN? That is a high level language because it uses natural language elements to make programing easier. It also hides or automates significant parts of the computing system such as memory management. This is called abstraction. • Ok, so now it is readable right? – Like beauty, readable is in the eye of the beholder. Here is that program in FORTRAN 1 Program Hello 2 Print *, "Hello World!" 3 End Program Hello • Nice, but if a computer only reads binary how do we get that higher level language back to binary? – Thought you would never ask! Programming Languages • Going from a High-Level Language to Machine Code • Issues of Note: – Machine code is unique to that CPU – Assembly Language is unique to particular computer architecture – High-level Languages are portable – This flow chart is missing the Linker Programming Languages • Compiler (Women and Comma Example) – Translates source code in a specific set of assembly language. – Lexical Analysis • Breaks the code into tokens which are pieces of the code that a unique such as keyword, variable names, etc. – Syntax/Semantic Analysis • Syntax: The tokens are parsed. Parsing is the analysis of a sentence or command to determine the exact meaning. Parse Tree is created. • Semantic: Semantic information is compared to the parse tree and determines if the tokens relate correctly. – Produces a file of containing assembly language • Assembler – Produces the an Object File for a CPU. This is not an executable file • Linker – Takes object code and creates an executable file Programming Languages •This seems really stupid. What crack pot two bit hack came up with this system!? Programming Languages • Rear Admiral Grace Murray Hopper, that’s who! – Coined the term “debugging” – Developed the Harvard 1, which is basically the computer that modern device are modeled on. – Wrote COBOL and the compiler for it – Has a US Navy Destroyer named after her – Earn a PhD in Mathematics from Yale in 1934 – Nicknamed “Amazing Grace” and “Grandma COBOL” – Known for her irreverent speaking style. – Jay Elliot described Grace Hopper as appearing to be "'all Navy', but when you reach inside, you find a 'Pirate' dying to be released" Programming Languages • Right, I take back my previous comment and would like to state for the record that the compiler is the coolest thing ever and the Dr. Hopper is awesome • So Java works pretty much the same, right? – Yes and no Programming Languages • Java Virtual Machine – Java got around the issues of OS and Hardware compatibility with the Virtual Machine. – It is a run-time environment that handles the assembly and linking on it’s own – It was the first “write once, run anywhere” code. • A Bit of History – The big computing companies wouldn’t allow certain developers to have the assembly and linker codes so they could write for their software (Microsoft and Apple, I am looking at you) – Sun Microsystems got around this with the Virtual Machine which enabled anyone to write in Java and have the program be compatible with any VM-enabled machine – This led to the expansion of the internet and the bigger companies to stop their silly feud… well until the Patent Wars which is a different story Programming Languages • Java Compiler – Creates byte code which is read by the VM – Bytecode is unique to the VM and cannot be assemble – The VM is written for a particular type of machine and executes the bytecode – Byte code files are *.class files. Programming Languages • We will be writing *.java files (Source Code) which will be our programs • The javac command will produce the *.class files – NOTE: The Java Compiler is still a compiler. It will check your code and throw errors • We will also increase our Awesome Rating throughout the year. Programming Languages Programming Languages Programming Languages