Programming Languages 2 Programming Languages

Previously What is a computer? Components Encoding Fast processor of data (input) to produce a result (output) Components Hardware Software BIOS, OS, Programs Encoding Units of storage Bit, Byte, KB, MB, GB and TB Representations Decimal, binary and hexadecimal CPU Power and data cables Speaker Ventilation Memory Hard drive RAM Power supply Motherboard Speed in a computer is normally measured by the clock speed of the CPU, units Hertz (Hz, cycles per second). In computers today in the order of 2GHz. Hardware

Overview What is a programming language? Languages by implementation Language by paradigm Simple initial design

What is a programming language? Set of grammatical rules for instructing a computer to perform specific tasks Languages based on their hierarchy; on how close they are to what the computer understands Machine Language Assembly Language High Level Languages C Pascal Fortran C++ C# Java LOWER HIGHER

Languages by implementation Machine language The lowest-level programming language Collection of binary digits (bits) that the computer reads and execute Machine language is the only language a computer is capable of understanding Assembly language symbolic representation of the binary machine codes and other constants needed to program a particular CPU architecture

Languages by implementation Compiled languages Languages that require a compiler program to turn programming source code into an executable machine-language binary program Stages Write source code Compile the written code by executing the compiler Output is the executable file (application); machine code Execute application Examples: Fortran, Pascal, C and C++

Languages by implementation Interpreted languages Interpreted program is converted to binary at runtime, by an interpreter program Java is an interpreted language The interpreter program is the Java Virtual Machine (JVM) Source Code Storage CPU/Memory Interpreter Machine Code Program Executed

Languages by implementation Interpreted languages (cont.) Interpreted languages tend to be slower than compiled ones Do not require compilers Usually easier to program than compiled languages Run in different machine without need to re-compile (just if machine has installed the interpreter) Specifically in Java there are mostly a free Java Library for everything

Language by paradigm Procedural Concurrent Object Oriented Derived from structured programming Series of computational steps to be carried out Concurrent Use element of concurrency Elements: threads, distributed computing, shared resources, message passing Object Oriented Uses objects; data structures consisting of data fields (information) and methods (functionality)

Simple initial design Create sequence of instructions to make two cups of tea Fill Kettle Boil Kettle Make tea - Get kettle - Go to tap - Put kettle under tap - Open tap - Wait until kettle full - Close tap - Place kettle on hob - Switch kettle on - Wait until boiling - Switch kettle off Get two cups Get two spoons - Get two tea bags Get sugar Put tea bags in cups Fill cups Serve cups, spoons & sugar The idea is that design starts by understanding the problem, followed by expressing what it is required in a simple way. Pseudocode helps to achieve it. “Pseudocode is a compact and informal high-level description of a computer programming algorithm that uses the structural conventions of a programming language, but is intended for human reading rather than machine reading” Wikipedia online. Different levels of Pseudocode depending of how close is to normal language or to programming language.

Simple initial design Different diagrams to represent what it is required Flow Chart Unified Modelling Language (UML) Includes a set of graphic notation techniques to create visual models of software Behaviour diagrams Used extensively to describe the functionality of software systems Activity diagram: describes the business and operational step-by-step workflows of components in a system. UML state machine diagram: describes the states and state transitions of the system. Use case diagram: describes the functionality provided by a system in terms of actors, their goals represented as use cases, and any dependencies among those use cases.

Simple initial design Make two cups of tea Fill Kettle - Get kettle Go to tap Fill Kettle Put kettle under tap - Get kettle - Go to tap - Put kettle under tap - Open tap - Wait until kettle full - Close tap Open tap Wait no Full? yes Close tap

Simple initial design Fill Kettle ... Boil Kettle Place kettle on hob Boil Kettle Switch kettle on - Place kettle on hob - Switch kettle on - Wait until boiling - Switch kettle off Wait no Boiling? yes Switch kettle off

Serve cups, spoons & sugar Simple initial design Fill Kettle Get two cups ... Get two spoons Boil Kettle ... Make tea Get two tea bags Get two cups Get two spoons - Get two tea bags Get sugar Put tea bags in cups Fill cups Serve cups, spoons & sugar Get sugar Put tea bags in cups Fill cups Serve cups, spoons & sugar

Serve cups, spoons & sugar Simple initial design Make two cups of tea Make tea Fill Kettle Boil Kettle Get two cups Get kettle Place kettle on hob Get two spoons Go to tap Switch kettle on Get two tea bags Put kettle under tap Wait Get sugar Open tap no Boiling? Put tea bags in cups Wait yes no Switch kettle off Full? Fill cups yes Close tap Serve cups, spoons & sugar

Simple initial design Divide project into smaller and simpler subprojects Use pseudocode to represent the project May help to understand the problem Simplify the coding Simpler to understand, more event for no programmers Flow chart may help to show the project to others Always document what you design and code Other graphical approaches exist to help in the design stage. We’ll see more about coding using Javadoc.