1 / 29

Objects, Classes, and Primitive Types in Java

Learn about objects, classes, and primitive types in Java programming, including syntax and semantics, state and behavior of objects, and the principles of code re-use and defining interfaces.

vneely
Download Presentation

Objects, Classes, and Primitive Types in Java

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. IAT 800 Lecture 5 Objects, Classes IAT 800

  2. Today • Primitive types • byte, short, int, long • Object-oriented programming • objects • classes • sets (mutators) and gets (accessors) • object methods IAT 800

  3. Primitive types • Primitive types are determined by machine architecture byte: 8bits reference: (JVM Dependent) short: 16bits int: 32bits long: 64bits float: 32bits double: 64bits IAT 800

  4. Reference • Like a remote control • a reference is a primitive thing that points at objects • the new keyword causes the reference to point at a new instance of the object IAT 800

  5. IAT 800

  6. Arrays • int[] nums = new int[7] ; IAT 800

  7. Array of objects • Dog[] pets = new Dog[7]; • It starts as an array of null references IAT 800

  8. Array of objects Dog[] pets = new Dog[7] ; pets[0] = new Dog(); pets[1] = new Dog(); IAT 800

  9. Objects IAT 800

  10. Real Objects • Real-world objects have • State • Behavior • Bicycle • State • selected gear, current pedal cadence, speed • Behavior • Change Gear, Set Cadence, Apply Brakes IAT 800

  11. Software Object • State int gear ; float speed ; float cadence ; • Behavior ChangeGears(int g); Brake( float level ); ChangeCadence( float c ); int GetGear(); float GetSpeed(); … IAT 800

  12. Java directly supports Objects • Java has direct syntactic and semantic support for Objects Syntax: class Bicycle { private int cadence = 0; private int speed = 0; private int gear = 1; void changeCadence(int newValue) { cadence = newValue; } void changeGear(int newValue) { gear = newValue; } } IAT 800

  13. Java directly supports Objects • Java has direct syntactic and semantic support for Objects Semantics: class Bicycle { private int cadence = 0; private int speed = 0; private int gear = 1; void changeCadence(int newValue) { cadence = newValue; } void changeGear(int newValue) { gear = newValue; } } Only these methods can read or write Bicycle private data IAT 800

  14. Java Semantic support • Programming usually takes place with objects: ClockClass clock = new ClockClass(); clock.setSecond( 12 ); clock.setMinute( 18 ); clock.setHour( 3 ); IAT 800

  15. Even Arrays are objects int[] bob = new int[10] ; bob[4] = 123 ; println( bob.size() ); Bicycle[] bikes = new Bicycle[10] ; bikes[0] = new Bicycle(); IAT 800

  16. Sets and Gets • what can you do with private data? • to set it: setVarName( varType newValue) • to get it: varType getVarName() • Why? IAT 800

  17. temperature object class temp { private float kelvin ; void setCelsius( float C ) { if( C < -273.15 ) return ; // perhaps an error message would be in order else kelvin = C + 273.15 ; } float getCelsius() { return( kelvin - 273.15 ); } void setKelvin( float k ) { if( k < 0 ) return ; else kelvin = k ; } } IAT 800

  18. temperature object • Controls access • Ensures correctness • can only run a setXYZ() to change temp • can only do getXYZ() to get the value in the desired scale • Who cares? IAT 800

  19. Who cares? • When you want to: • Solve the problem once and forget it • Reuse the solution elsewhere • Establish rules for use and change of data • The principle: • Information hiding • By interacting only with an object's methods, the details of its internal implementation remain hidden from the outside world. IAT 800

  20. Principle: Code re-use • If an object already exists, you can use that object in your program. • Specialists build, you use IAT 800

  21. Principle: Define the Interface • Define the interface: • The list of methods with Defined Operation • The interface is the thing that other people use • If you have the same interface with the same meaning • You can plug in a better implementation! IAT 800

  22. Define the Interface • If you have the same interface with the same meaning • You can plug in a better implementation! • You can plug in a More Interesting implementation! IAT 800

  23. Summary of principles • Hide unnecessary details • Clearly define the interface • Allow and support code re-use • Build on the work of others IAT 800

  24. How do we build on other work? • Divide and conquer • Cut the problem into smaller pieces • Solve those smaller problems • Aggregate the smaller solutions • Two approaches: • Top-down • Bottom-up IAT 800

  25. IAT 800

  26. Top Down • Take the big problem • Cut it into parts • Analyze each part • Design a top-level solution that presumes you have a solution to each part • then… • Cut each part into sub-parts IAT 800

  27. Bottom-up • Cut the problem into parts, then sub-parts, then sub-sub parts… • build a solution to each sub-sub-part • aggregate sub-sub solutions into a sub-solution IAT 800

  28. How do we build on other work? • Recognize the problem as another problem in disguise • It’s a sorting problem! • It’s a search problem! • It’s a translation problem! • It’s an optimization problem! IAT 800

  29. The challenge • Software design is typically done top-down • Software implementation is typically done bottom-up IAT 800

More Related