Lab 5 Random numbers!

Transcription

1 Lab 5 Random numbers! ADT:s as Programming Tools! D0010E! Lecture 13! Iterators! MasterMind Reminder: Groups must have their designs approved before any actual programming is allowed to start. Some review sessions will also be available on Tuesday, but opt for those on Monday of you can (gives you more time). Extra help with design and UML. Copies handed out now. Extra-extra help concerning lab 5 found! A precious napkin from a meeting in a restaurant somewhere close... ADT:s as programming tools An Abstract Data Type (ADT) gives an abstract view on a class of objects. States what objects are and do, not how this is achieved in code. Formulating parts of programs as ADT:s makes it easier to program since implementation details can be ignored until later. To finally get a working program, code must of course be supplied. 4

2 Design! Coding! When reading Riley In fact, if you read Part 3 in the course compendium carefully, programs (a class) are often presented in five (5) ways: Informal: An informal description of a kind of object and maybe even a picture. Design: An ADT specification. What is an object like this, what can it do, and what is true about it and its actions? Design: A UML-diagram. Show details and relationships with other ADT:s (their UML-diagrams). Coding: An implementation of the ADT as an abstract class or an interface. Idea: Keep the abstract view separated from the implementation view. Coding: A concrete implementation of a class that is faithful to the ADT. Pure working code! 5 Representation To implement an ADT involves choosing a representation. The representation is the concrete data that is used in the implementation to achieve what the ADT stands for. Major questions: What variables should be used? What should their types be? How should these variables be used? 6 Example: AlarmClock Fig. 1.3, 1.6, handout about AlarmClock. Note that AlarmClock makes use of TimeOfDay but is independant of its particular implementation. AlarmClock is a client of TimeOfDay. The programmer that implements AlarmClock also acts as a client. The programmer only needs the abstract view of TimeOfDay provided by the ADT and the UML diagram. Test-run! Handout AlarmClock 7 8

3 Iterators Riley 2.9, 4.4 An iterator is an object the provides the possibility to access ( visit ) all items of a container one at a time. A very common operation in computer programs. Iterator Design Pattern Fig 2.18 interface Iterator Note that the container class has a method that returns an iterator. Visits to items in a container are made via this iterator object, not the container itself. Since the iterator class is an inner class of the container class, it can access everything in the (outer) container class. Fig 2.18 Iterator Design Pattern! Fig 4.14 SimpleSequence UML import java.util.*; public abstract class SimpleSequenceADT { public SimpleSequenceADT (int m ) { public int size() { Object temp; int result = 0; Iterator it = iterator(); while ( it.hasnext() ) { temp = it.next(); result++; return result; public Object ith( int i ) { if (i < 1) { throw new NoSuchElementException(); Object result = null; Iterator it = iterator(); for (int j=i; j!=0; j--) { result = it.next(); return result; public abstract void concatitem( Object z ); public abstract Iterator iterator();

4 import java.util.*; public class SimpleSequenceArray extends SimpleSequenceADT { private int count; private Object[] seqitems; private class SimpleSequenceIterator implements Iterator { private int itemsprobed; public SimpleSequenceArray( int m ) { super(m); seqitems = new Object[m]; count = 0; public int size() { return count; public Object ith( int i) { return seqitems[i-1]; public void concatitem( Object z ) { if (count == seqitems.length) { throw new IllegalStateException(); else { seqitems[count] = z; count++; public SimpleSequenceIterator() { itemsprobed = 0; public Object next() { if (itemsprobed == count) { throw new NoSuchElementException(); else { itemsprobed++; return seqitems[itemsprobed-1]; public boolean hasnext() { return itemsprobed < count; public void remove() { throw new UnsupportedOperationException(); public Iterator iterator() { return new SimpleSequenceIterator(); The for-each loop MasterMind The elements in the array/collection can only be accessed, not changed. MasterMind is a board game for two players. A code breaker tries to guess a secret code while the codemaker gives cryptic feedback on the guesses. To program MasterMind one can proceed as in the handout.

5 Design discussion Identify classes, and relationships between them. What is the responsibility of each class? If you know this, it is relatively easy to modify the design. Random Examples of how randomness can be used in Java. Note: This is not true randomness but pseudo-randomness (very good but fake).