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Object Oriented Program Terms

***** SWTJC STEM *****. An object is a fundamental entity in a Java program. OO ( O bject O riented) programming has been around since the 1960’s in one form or another. In 1980’s and 1990’s it’s popularity increased enormously with the introduction of C++ and then Java.

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Object Oriented Program Terms

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  1. ***** SWTJC STEM ***** • An object is a fundamental entity in a Java program. • OO (Object Oriented) programming has been around since the 1960’s in one form or another. • In 1980’s and 1990’s it’s popularity increased enormously with the introduction of C++ and then Java. • One reason for its popularity is that objects can represent real world entities like an employee in a company or a bank account. • You might be asked to write a procedure oriented program to balance a bank account. When finished, it would do just that the one task. • By creating the bank account as an object, you create a program that can capture many more aspects. In addition to balancing the account, you could also handle service charges or interest, post a check, etc. Object Oriented Program Terms Chapter 2-1 cg 17

  2. ***** SWTJC STEM ***** • The terms you need to know in OO programming include: • object • attribute • method • class • encapsulation • inheritance • polymorphism • We will study these terms in greater detail as the course progresses. For now, we will use very brief definitions. Object Oriented Program Terms Chapter 2-1 cg 17

  3. ***** SWTJC STEM ***** • object – The fundamental element in an OO program. • attribute – Object values that are stored internally. Attributes “remember” the states or properties of the object. • method – A group of programming statements, given a name, and executed when invoked. Methods define the behaviors of the object. • class – The model from which the object is created. The class defines the properties (states) and behaviors of the object. • encapsulation – A object protects and manages its own properties. Other objects cannot “reach in “ and change an objects properties. • inheritance – The definition of one class can be based on another class, creating a hierarchy of classes. • polymorphism - The ability of different objects to respond differently to the same message. Object Oriented Program Terms Chapter 2-1 cg 17

  4. ***** SWTJC STEM ***** Procedure Oriented Solution Cylinder Volume Calculate Volume of Cylinder V = PI * r2*h Radius r Cylinder Volume Height h Note that the solution does only one thing, calculate V. Chapter 2-1 cg 18

  5. ***** SWTJC STEM ***** Object Oriented Solution Cylinder Volume Cylinder Object Attributes r radius h height V volume ----------------------- Methods Set r, h Get r, h, V Messages to/from ObjectsetRadius(5) setHeight(10) getRadius( ) returns 5 getHeight( ) returns 10 getVolume( ) returns 785 Chapter 2-1 cg 18

  6. ***** SWTJC STEM ***** Messages to/from ObjectsetRadius(5) setHeight(10) getVolume( ) returns 785 emptyTank( ) getTotal( ) returns 0fillTank( ) getTotal( ) returns 785 emptyTank( ) add(100) getTotal( ) returns 100 add(50) getTotal( ) returns 150 remove(80) getTotal( ) return 70 Tank Object Object Oriented Solution Cylindrical Tank Simulation Attributes r radius h height V volume T total liquid ----------------------- Methods set r, h get r, h, V, T empty, fill add, remove Chapter 2-1 cg 18

  7. ***** SWTJC STEM ***** • The PO program does only thing, calculate volume. • The OO program does many things. • It would take several PO programs packaged together (to make them accessible) to accomplish the same thing. • Methods of an OO program are actually PO programs collected together and organized to make them readily accessible. • This fact is why we will study and use many of the principles of PO programming when developing OO programs. • Before proceeding, we need to talk about two more concepts: • Programsyntax and semantics • Programerrors In Summary Chapter 2-1 cg 18

  8. ***** SWTJC STEM ***** • Syntax refers to the rules for writing a program statement. • These rules must be followed in creating a program. • Example: “prntln” is bad syntax. Why? • “prntln” is missing the “i” and should be “println”! • Appendix L of the text defines the syntax rules of Java. • JBuilder will often help you find incorrect syntax before you execute the program. • The semantics of a program statement defines what will happen when the statement is executed. • Programming languages are generally unambiguous, which means there is one and only one interpretation of a statement. • The question is whether the interpretation is the one you wanted. If not, the program may do something you did not intend. Syntax and Semantics Chapter 2-1 cg 19

  9. ***** SWTJC STEM ***** • A computer program may have problems that prevent it from executing correctly. • These problems, or errors, take three forms: • syntax errors (compile-time) • Spelling “println” wrong is a syntax error. • JBuilder generally finds these. • semantic errors (run-time) • Dividing by zero happens at run time and is a semantic error. • Semantic errors usually cause a program to terminate abnormally. • logic errors • Program executes but produces incorrect results. • Programs must be tested thoroughly and “debugged” Computer Program Errors Chapter 2-1 cg 20

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