Kernel Implementations I. 27 June 2013 OSU CSE 1

Transcription

1 Kernel Implementations I 27 June 2013 OSU CSE 1

2 So, What s Inside the Computer? Consider any popular video game, e.g., Nintendo Wii bowling Are there bowling balls and bowling pins inside the game console s computer? 27 June 2013 OSU CSE 2

3 So, What s Inside the Computer? Consider any popular video game, e.g., Nintendo Wii bowling Are there bowling balls and bowling pins inside the game console s computer? Of course not! What s really inside the computer, then, that makes bowling-like behavior? 27 June 2013 OSU CSE 3

4 So, What s Inside the Computer? Consider any popular What video dynamic game, behavior e.g., Nintendo Wii bowling Are there bowling balls and and could bowling see inside pins the inside the game console computer computer? at any level of Of course not! A thought experiment: would you see if you had a magical magnifying glass detail while it s running? What s really inside the computer, then, that makes bowling-like behavior? 27 June 2013 OSU CSE 4

5 A Useful Metaphor 27 June 2013 OSU CSE 5

6 A Tower of Abstractions Bowling pins? Vectors? Numbers? Bits? Voltages? Electrons???? 27 June 2013 OSU CSE 6

7 A Tower of Abstractions Bowling pins? Vectors? Numbers? Bits? Voltages? Electrons???? These are all just mathematical models, i.e., abstractions used to explain and predict behavior. 27 June 2013 OSU CSE 7

8 A Tower of Abstractions Bowling pins? Vectors? Numbers? Bits? Voltages? Electrons???? Domain: Physics These models are supposed to match physical reality, and are discarded if they do not; limited by the physical world. 27 June 2013 OSU CSE 8

9 A Tower of Abstractions Bowling pins? Vectors? Numbers? Bits? Voltages? Electrons???? Domain: Computing These models are entirely artificial (need not match physical reality); limited only by the creativity of the software engineer. 27 June 2013 OSU CSE 9

10 A Tower of Abstractions Bowling pins Vectors Numbers Bits Voltages Electrons??? 27 June 2013 OSU CSE 10

11 A Tower of Abstractions Bowling pins Vectors Numbers Bits Voltages Electrons??? Numbers may be built on top of bits 27 June 2013 OSU CSE 11

12 A Tower of Abstractions Bowling pins Vectors Numbers Bits Voltages Electrons??? Bits may be built on top of voltages 27 June 2013 OSU CSE 12

13 A Tower of Abstractions Bowling pins Vectors Numbers Bits Voltages Electrons??? Voltages may be built on top of (?) electrons 27 June 2013 OSU CSE 13

14 Interpretation of Representation Let s not take the tower-building metaphor too far! A better approach is to think about interpreting a lower-level configuration (a.k.a. a representation) to get a higherlevel value 27 June 2013 OSU CSE 14

15 A Tower of Abstractions Bowling pins Vectors Numbers Bits Voltages Electrons??? (Configurations of) bits may be interpreted as numbers June 2013 OSU CSE 15

16 A Tower of Abstractions Bowling pins Vectors Numbers Bits Voltages Electrons??? (Configurations of) voltages may be interpreted as bits 27 June 2013 OSU CSE 16

17 A Tower of Abstractions Bowling pins Vectors Numbers Bits Voltages Electrons??? (Configurations of) electrons may be interpreted as voltages 27 June 2013 OSU CSE 17

18 First Example: QueueKernel For QueueKernel, one idea is to represent a Queue variable s value by using a java.util.list variable By convention (of the OSU CSE components), a kernel class that directly represents the new type using a component from the Java libraries that is very similar, has a name ending in L In this case, it is called Queue1L 27 June 2013 OSU CSE 18

19 Detailed Example: Queue1L What existing components (including builtin types of Java, and the Java libraries) could you build it on top of? In other words, what could you use as a data representation that could be interpreted as a Queue value? 27 June 2013 OSU CSE 19

20 Context of Queue1L Standard Iterable Has bodies for the constructor, plus the 7 methods from Standard and QueueKernel. QueueKernel Queue Queue1L extends extends implements QueueSecondary extends extends extends Object 27 June 2013 OSU CSE 20

21 Context of Queue1L newinstance clear transferfrom constructor enqueue dequeue length iterator Standard extends QueueKernel extends Queue extends Iterable Object implements QueueSecondary extends Queue1L extends 27 June 2013 OSU CSE 21

22 Instance Variables Each separate Queue1L object has its own distinct java.util.list variable that represents its object value Note: In the code we will examine for Queue1L, there is a declaration of a private instance variable whose value is the java.util.list that represents one Queue1L object (namely, this) 27 June 2013 OSU CSE 22

23 Instance Variables The adjective instance means there is a distinct variable (with the same name) for each instance (i.e., each distinct object) of the class in which it is declared. Each separate Queue1L object has its own distinct java.util.list variable that represents its object value Note: In the code we will examine for Queue1L, there is a declaration of a private instance variable whose value is the java.util.list that represents one Queue1L object (namely, this) 27 June 2013 OSU CSE 23

24 Let s Look at Queue1L.java 27 June 2013 OSU CSE 24

25 Other Representations? Is there any other way to use a java.util.list to represent an object value of type Queue? 27 June 2013 OSU CSE 25

26 Other Representations? Is there any other way to use a java.util.list to represent an object value of type Queue? Yes! What if you simply thought of the front of the Queue as being at the right end of the java.util.list rather than the left? How would the code change with this reversed interpretation? 27 June 2013 OSU CSE 26

27 Resources OSU CSE Components API: Queue 27 June 2013 OSU CSE 27