You have seen abstractions in many places, lets consider them from the ground up.

Transcription

1 CS1706 Intro to Object Oriented Dev II - Fall 04 Announcements Week 10 Project 2 due 11/01 Material Interfaces Anonymous classes

2 Lets see abstractions... You have seen abstractions in many places, lets consider them from the ground up. Expressions Functions (with no arguments) Functions with arguments Functions in a separate class Functions in an interface Each has different forms of reuse compilation, invocation, execution, programs, etc.

3 Different levels System.out.println(3 + 4); function void doadd() { System.out.println(3 + 4); function int doadd() { return 3 + 4; System.out.println(doAdd()); function int doadd(int a, int b) { return a + b; class Add { function int doadd(int a, int b) { return a + b; Add a = new Add(); System.out.println(a.doAdd()); Expressions Functions (with no arguments) Functions with arguments Functions with arguments Functions in a separate class

4 Interfaces one more level Famous saying in CS Anything can be done with one more level of indirection If someone didn't understand their code and its likely uses well enough to write brief useful comments, why should I imagine that they understood it well enough to write code that works? -- Richard A. O'Keefe When I am working on a problem, I never think about beauty. I think only of how to solve the problem. But when I have finished, if the solution is not beautiful, I know it is wrong. -- R Buckminster Fuller As soon as we started programming, we found out to our surprise that it wasn't as easy to get programs right as we had thought. Debugging had to be discovered. I can remember the exact instant when I realized that a large part of my life from then on was going to be spent in finding mistakes in my own programs. -- Maurice Wilkes

5 LinearSearch Revisited 068: static boolean linearsearch(object[] data, 069: Object target) { 070: 071: assert(data!= null); 072: assert(target!= null); 073: int index = 0; 074: boolean found = false; 075: 076: while (!found && index < data.length) { 077: if (data[index].equals(target)) 078: found = true; 079: index++; 080: 081: 082: return found; 083: Abstract out a comparison between data[index] and target. Need True if they are same, False otherwise

6 Abstraction Comparator interface in Java interface Comparator { int compare(object o1, Object o2); We had to abstract out if (data[index].equals(target)) Then it becomes comp.compare(data[index++], target) == 0 Where comp is of type Comparator and somehow must be provided

7 Linear w/comparator 094: static boolean linearsearch( 095: Object[] data, Function Object 096: Object target, 097: Comparator comp) { 098: 099: assert(data!= null); 100: assert(target!= null); 101: assert(comp!= null); 102: int index = 0; 103: boolean found = false; 104: 105: while (!found && index < data.length) { 106: if (comp.compare(data[index++], target) == 0) 107: found = true; 108: index++; 109: 110: 111: return found; 112:

8 Clients of linear search Before the change... if (Search.linearSearch(array, target)) found it Now... if (Search.linearSearch(array, target, comp)) found it Where comp.compare() must do this (data[index].equals(target)) So what we have is: class mycompare implements Comparator { int compare(object o1, Object o2) { return (o1.compareto(o2));

9 Result 01: class mycompare implements Comparator { 02: int compare(object o1, Object o2) { 03: return o1.compareto(o2); 04: 05: 06: 07: public class Main { 08: public static void main(string[] args) { 09: Comparator comp = new mycompare(); 10: // code omitted here 11: if (Search.linearSearch(array, target, comp)) 12: System.out.println("Found it"); 13: else 14: System.out.println("No found"); 15: 16:

10 Better (anonymous obj) 01: class mycompare implements Comparator { 02: int compare(object o1, Object o2) { 03: return o1.compareto(o2); 04: 05: 06: Anonymous Object 07: public class Main { 08: public static void main(string[] args) { 09: // code omitted here 10: if (Search.linearSearch(array, target, 11: new mycompare())) 12: System.out.println("Found it"); 13: else 14: System.out.println("No found"); 15: 16:

11 What? 01: public class Main { 02: public static void main(string[] args) { 03: // code omitted here 04: if (Search.linearSearch(array, target, 05: new Comparator() { 06: int compare(object o1, Object o2) { 07: return o1.compareto(o2); 08: 09: )) 10: System.out.println("Found it"); 11: else 12: System.out.println("No found"); 13: 14: Anonymous Class ( inner class )