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Lecture on object oriented programming.ppt
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- 2. Java! Java isa language characterized by buzzwords – buzzword: A trendy word or phrase that is used more to impress than explain From Sun Microsystems, the developers of Java: What do all of those terms mean? “Java is a simple, object-oriented, distributed, interpreted, robust, secure, architecture-neutral, portable, high performance, multi-threaded, and dynamic language.”
- 3. A programminglanguage – a vocabulary and set of syntactical (grammatical) rules for instructing a computer to perform specific tasks – you can do most anything in any programming language – a particular language encourages one to do things in a certain way Question: Is this a fair characterization? “Java is a simple, object-oriented, distributed, interpreted, robust, secure, architecture-neutral, portable, high performance, multi-threaded, and dynamic language.”
- 4. Based onpopular languages called C and C++ C: old, pretty bare bones language C++: newer, more complicated language Start from C and add some of C++’s more useful features “Java omits many rarely used, poorly understood, confusing features of C++ that in our experience bring more grief than benefits” (Gosling) Question: Is Java really all that simple? “Java is a simple, object-oriented, distributed, interpreted, robust, secure, architecture-neutral, portable, high performance, multi-threaded, and dynamic language.”
- 5. The object-orientedparadigm – problems and their solutions are packaged in terms of classes – the information in a class is the data – the functionality in a class is the method – a class provides the framework for building objects Object-oriented programming (OOP) allows pieces of programs to be used in other contexts more easily “Java is a simple, object-oriented, distributed, interpreted, robust, secure, architecture-neutral, portable, high performance, multi-threaded, and dynamic language.”
- 6. A distributedsystem is one where multiple separate computer systems are involved – the Internet is a very large distributed system • interconnected collection of computer networks • heterogeneous components • large number of services: WWW, file services, audio/video channels Java was designed for the web “Java is a simple, object-oriented, distributed, interpreted, robust, secure, architecture-neutral, portable, high performance, multi-threaded, and dynamic language.”
- 7. Java ahigh-level language High-level languages must be translated to a computer’s native tongue, machine language Interpreted high-level languages are translated to an intermediate form and then converted to machine language and run – Java bytecodes – bytecode (class) file is executed by a Java bytecode interpreter “Java is a simple, object-oriented, distributed, interpreted, robust, secure, architecture-neutral, portable, high performance, multi-threaded, and dynamic language.”
- 8. Programs willhave errors, but a good program degrades reasonably A robust program may not do exactly what it is supposed to do, but it should not bring down other unrelated programs down with it Reliability – early (compile time) checking – dynamic (runtime) checking – eliminating situations that are error prone. “Java is a simple, object-oriented, distributed, interpreted, robust, secure, architecture-neutral, portable, high performance, multi-threaded, and dynamic language.”
- 9. Security – techniquesthat ensure that data stored on a computer cannot be read or compromised Java is intended for use in networked/distributed environments – a program is running on your computer … what is to stop it from erasing all of your data, accidentally or otherwise? Java enables the construction of virus-free, tamper-free systems – authentication based on public-key encryption “Java is a simple, object-oriented, distributed, interpreted, robust, secure, architecture-neutral, portable, high performance, multi-threaded, and dynamic language.”
- 10. A languageis architecture-neutral if it does not prefer a particular type of computer architectures Example: – not too hard to construct a program that will run faster on a Macintosh than on a PC, and vice-versa – each have their own respective strengths and weaknesses A particular program is never entirely architecture neutral though Question: When is being architecturally neutral a bad thing? “Java is a simple, object-oriented, distributed, interpreted, robust, secure, architecture-neutral, portable, high performance, multi-threaded, and dynamic language.”
- 11. Program once,run anywhere A program is portable if it will work the same (more or less) on many different computer systems – platform-independent Much effort is currently spent porting non-portable code Java has no "implementation dependent" aspects HTML is also portable or platform-independent “Java is a simple, object-oriented, distributed, interpreted, robust, secure, architecture-neutral, portable, high performance, multi-threaded, and dynamic language.”
- 12. Performance: speedin completing some task – performance is everything to most computer and software manufacturers! Think about this … – if the transportation industry kept up with the computer industry, one would be able to now buy a Rolls Royce that could drive across country in 5 minutes for $35 However … – it would crash once a week, killing everyone on board “Java is a simple, object-oriented, distributed, interpreted, robust, secure, architecture-neutral, portable, high performance, multi-threaded, and dynamic language.”
- 13. A threadis a part of the program that can operate independently of its other parts Multi-threaded programs can do multiple things at once – example: • download a file from the web while still looking at other web pages Question: What is the problem with multiple agents working at the same time? – synchronization “Java is a simple, object-oriented, distributed, interpreted, robust, secure, architecture-neutral, portable, high performance, multi-threaded, and dynamic language.”
- 14. Dynamic: actionsthat take place at the moment they are needed rather than in advance – antonym: static A dynamic program can – ask for more or less resources as it runs – use the most recent version of some code that is available Question: Why is being dynamic a good thing? – upgrades “Java is a simple, object-oriented, distributed, interpreted, robust, secure, architecture-neutral, portable, high performance, multi-threaded, and dynamic language.”
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- 16. Trees Hierarchical datastructure Set of elements or nodes – one node as root – every other node has a single predecessor (parent) and zero or more successors (children) – nodes without successors are called leaf nodes Nodes are connected by edges The level or depth of a node is the number of edges on the path to the root The depth of the tree is the number of edges on the longest path from root to any leaf A complete tree has all leaves at same level, all other nodes have the same number of children
- 17. Example tree structure leaf leaf leaf leaf leaf root leaf depth of tree = 3 edge
- 18. Decision trees Adecision tree begins with a decision you need to make – start with an initial decision node – ask a question Structure for investigating options and the possible outcomes of choosing those options – result of a decision can be another decision – outcome is a terminal node Tree should have unique paths from the decision node to each of the terminal nodes. – help you to choose between several courses of action
- 19. Examples Real lifedecision trees – which route to take to class? – which {cell phone, computer, camera} is best for me? – what to wear? – where to go on vacation?
- 20. He received the PhysicsPrize in 1921. Try the Medicine Prize in 1962. Would you prefer a humanitarian? Would you like to read about a scientist? Would you like to read about Einstein? Try A. Solzhenitsyn, Literature 1970. Look up the Peace Prize in 1991. A Decision Tree yes yes yes no no no
- 21. A decision treefor sorting yes a b? b c? a c? no yes no a b c a c? a c b c a b yes no yes no b a c b c? b c a c b a yes no
- 22. Binary trees Nodeshave at most two children In a complete binary tree of depth 3, – how many nodes are in the tree? – how many leaves are in the tree? In a complete binary tree of depth 4, – how many nodes are in the tree? – how many leaves are in the tree? How many nodes in a depth d tree? How many leaves in a depth d tree?