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Classes / Objects / Methods

Classes / Objects / Methods. Chapter 4. Object Oriented Programming. Divides a program into Modules/Classes Uses Classes and Objects to simulate real world environments Basic Programming Components Classes Objects Methods. Class. Specifies the definition of a particular kind of object

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Classes / Objects / Methods

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  1. Classes / Objects / Methods Chapter 4

  2. Object Oriented Programming • Divides a program into Modules/Classes • Uses Classes and Objects to simulate real world environments • Basic Programming Components • Classes • Objects • Methods

  3. Class • Specifies the definition of a particular kind of object • Frog • Snowman • Cell phone • Blueprint / design for how to create an object of that type • Class names begin with a Capital letter

  4. Class • Properties • Characteristics • Methods • Behaviors

  5. Objects • Specific Instances of a Class • Implementation of the Class Definition • Spot  one specific dog • Frosty  one specific snowman • All specific objects of the same class share the same definition • Same Properties – can be modified • Same Methods – can be modified • Object names begin with lowercase letter

  6. All Instances of Class Dog Have Properties Name Breed Weight Color Methods Walk Bark Jump Each Instance Has Properties Spot Mutt 10 pounds Black Methods Walk Bark Jump (can be modified to fit Spot’s requirements) Dog Object

  7. Methods • Sequence of Instructions • Tasks that can be performed • Some are predefined within the Class • Dog has a bark method • Others are Created or Modified • Methods organize the program • Divide the program into manageable pieces

  8. Parameters • Pieces of Information that need to be sent to the Method • Turn Toward (what) • Turn Toward Snowwoman

  9. Levels of Methods • Global Methods (World Level) • Methods that reference more than one object • Class Methods • Methods that define a behavior for one single object

  10. Create New Method • Snowpeople (problem 4-1) • flipsHat • Raises right arm • Grabs Hat • Tips toward snowwoman • Returns Hat to Head • World Method • Uses snowman and snowwomen • World • Method • Create New Method • Name  flipsHat

  11. Add Method Instructions

  12. Calling a Method • New Method must be “Called” • Program Instructions must indicate to Execute the new Method • In Alice • Drag Method into World.MyFirstMethod • In Other Languages • Call the Method using Method Name

  13. Parameters • Allows communication with Methods • Communicate Values (Numbers, Colors) • Communicate Object Names

  14. Create Method with Parameter • Create Method called “dance” • Object will jump up and down and spin around • Create Parameters • Parameter 1 • Which object to dance • Parameter 2 • How many times to Spin

  15. Creating Parameter • Which object to Dance • Name • Arbitrary • Placeholder – holds place of the actual object the will be used in the method • Type: • Number • Boolean (True/False) • Object • Other (Sound, Color, Etc.)

  16. Parameters show in Upper Left of Method Panel When Method is Called (Used) Object must be sent as an Argument to Method Parameter

  17. Use Parameter in Method

  18. Calling Method with Parameter • When using Method you must include Parameter • Use dance method after flipHat • Example 1: Requires an object to dance

  19. Multiple Parameters • Add Second Parameter – How many times to Spin • Name: numberToSpin • Type: Number • Use in the Turn Instruction

  20. Modify Method Call • Change 2nd Parameter • Pick any 2 different numbers

  21. Create Another Method • Create a Method for Snowman Blinking His Eyes • Is this a World / Global Method • Is this a Class Method • Why • How is it Created?

  22. Homework • Chapter 4, Section 1 (4-1) • #3 – Gallop and Jump • #4 – Helicopter Flight • Chapter 4, Section 2 (4-2) • #6 – Frog Escape • Bring electronic copy of homework to class • Bring printed copy of homework to submit

  23. Class Methods • Class Methods are methods that define a behavior for one single class object. • Select Horse Object • Methods • Create New Method • gallop

  24. Guidelines for Class Methods • Create lots of class methods as necessary • Do not call world-level methods from within a class-level method • Do not use instructions for other objects from within a class-level method • You can use parameters to send necessary information instead of referring to other specific objects from within the method.

  25. Inheritance • Creating a class on a previously defined class • Adding functionality to existing class by defining new methods or editing existing ones • Different members of design team can work on different methods for the class

  26. Creating a New Class in ALICE • Save object with new class methods as a New Class • Code Reuse • Galloping Horse • 2 Step Process • Rename existing object in Object Tree • Save As a New Class

  27. Rename Object • Select the Object in the Object Tree • Right-Click • Rename • Select a New Meaningful Name for Object • GallopingHorse

  28. Save As New Class • Select the Object in the Object Tree • Right-Click • Save Object • Navigate to folder where you want to save the object Other objects: Alice\Alice\Required\Gallery .a2c extension  Alice 2.0 class

  29. New Class • New Class (GallopingHorse) is now available in Object Gallery • All objects of GallopingHorse • all methods of horse • class-method gallop

  30. Homework • Exercise 4-3 • #10 • #11  use a say instruction not a sound file so all worlds don’t have to import sound file • Bring electronic copy of homework to class • Bring printed copy of homework to submit

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