The document discusses the distinction between syntax and semantics in programming languages, explaining how syntax refers to the rules for constructing statements, while semantics pertains to the meaning of these statements. It covers the evolution from low-level languages to high-level languages, highlighting the role of compilers and interpreters in translating source code into executable machine code. Additionally, it details the compilation process, the function of Integrated Development Environments (IDEs), and the specific case of Java's bytecode and execution through the Java Virtual Machine (JVM).

1. Language Translators

2. Syntax vs Semantics
Syntax: rules that govern how statements in a
computer programming language must be
constructed.
 Incorrect spelling
 Wrong brackets
 Leave off matching brackets
 Leave off end statements
Semantics: meaning conveyed by collection
of statements.
Computers (compilers) detect SYNTAX
errors, but they cannot determine the purpose
of programs or semantic meaning (yet!!).

3. Low Level Languages
Inside the RAM programs are represented in
binary form (000101000111100110, machine
code language)
First step: created codes that stand for binary
instructions (ADD 2310, Assembly Language:
each line corresponds to one machine code
instruction). They are machine specific.
As this was still difficult to handle High
Level Languages

4. High Level Languages
Portable: can run in different machines
English-like
One instruction = many machine code instructions
More than 2000 languages developed
Early: FORTRAN (FORmula TRANslation lang),
COBOL (COmmon Business Oriented Language,
ALGOL (ALGorithic Lang: first structured lang which
led to C and PASCAL), BASIC (Beginners All-
purpose Symbolic Code)
Object Oriented Languages: SAMLLTALK, C++ and
JAVA.

5. Compiler
Translation program that converts source code into
object code format (from HLL to machine code to be
executed)
Checks for syntax errors and reports to programmer.
Programmer corrects source code and compiles
again.
If syntactically correct  compiler links modules and
generates required object code.
Compiled code usually executes faster than an
interpreted version and can be moved to other
computers.

6. IDE
Integrated Development Environment
Integrates editor (to create the code) +
debugger (allows programmer to
remove bugs from source code)

7. Compiler

8. Interpreter

9. Translation Process
(Summary)
Converts source code into object code
that can be executed
Compiled code:
completely separate prg
Can stand alone
Does not need the compiler to run
Code run via an interpreter can be
usually viewed.

10. Compiler
Creates a completely
new prg to be executed.
Does not stop at the
first error and continues
reporting syntax errors
found.
No need to load into
memory to execute a
compiled prg
The object code cannot
be modified
Analyses and executes
each line of source code
in succession
Does not look first to the
entire prg
Runs slower than
compiled prg
Line being interpreted is
executed straight away
(good for large prg)
Need to be loaded each
time  memory usage
Interpreter

11. Compiling & Running Java
Compiles to an intermediate stage: Java
bytecode
Java bytecode:
 Stage found in in a java .class file produced by running
the javac program on a Java source code file.
 compressed version then passed to an interpreter
(JavaVirtual Machine)
JVM actually produces the machine code from the
bytecode file and pre-compiled library units
needed by the Op System.

12. Java Source file
.java extension
javac compiler
Java library files
(.class files) for
local platform
Java bytecode file
with .class
extension
Java interpreter (Java
Virtual Machine)
Java machine code