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Python Plus Java in a
Three Course Sequence
David Ranum
Brad Miller
Luther College
We’d like them to look
like this
But many look more like
this
Want To Avoid This
Why do they end up
this way?
! Taxonomy of Problems in Teaching Java -- The Java Task Force
Difficulties Teaching Java in CS1 and How We Aim to Solve Them
! Taming the Tiger -- Teaching the next generation of Java
! The Dream of a Common Language: The search for Simplicity and Stability in
Computer Science
The original Pascal book by Wirth had 266 Pages, Dietel and Dietel has 1536
There are more public methods in the java and javax package heirarchies than
there are words in Wirth's book.
! Taming Java for the Classroom
! Java is the Canonical Lanuage for teaching introductory programming, but...
! Lots of Papers on help for teaching objects early
! BlueJ
! ObjectDraw
! Karel J Robot
! Java Task Force Libraries
Why do they end up
this way?
! Taxonomy of Problems in Teaching Java -- The Java Task Force
! Taming the Tiger -- Teaching the next generation of Java
! The Dream of a Common Language: The search for Simplicity and Stability in
Computer Science
The original Pascal book by Wirth had 266 Pages, Dietel and Dietel has 1536
There are more public methods in the java and javax package heirarchies than
there are words in Wirth's book.
! Taming Java for the Classroom
!Java is the Canonical Lanuage for teaching
introductory programming, but...
! Lots of Papers on help for teaching objects early
! BlueJ
! ObjectDraw
! Karel J Robot
! Java Task Force Libraries
Why do they end up
this way?
! Taxonomy of Problems in Teaching Java -- The Java Task Force
! Taming the Tiger -- Teaching the next generation of Java
! The Dream of a Common Language: The search for Simplicity and Stability in
Computer Science
The original Pascal book by Wirth had 266 Pages,
Dietel and Dietel has 1536
There are more public methods in the java and
javax package heirarchies than there are words in
Wirth's book.
! Taming Java for the Classroom
! Java is the Canonical Lanuage for teaching introductory programming, but...
! Lots of Papers on help for teaching objects early
! BlueJ
! ObjectDraw
! Karel J Robot
! Java Task Force Libraries
The Java Magic Spell?
Increasingly, people seem to misinterpret
complexity as sophistication, which is baffling the incomprehensible should cause suspicion
rather than admiration. (Niklaus Wirth)
What Can We Do?
Join the folks trying to fix Java or...
Use a Language that encourages students to
focus on problem solving and computer
science
As Moti-Ben Ari put it in SIGCSE 2005
Keynote: “Its OK to teach introductory
Physics students about levers and pulleys”
Its OK to start out on the Green Runs
Hello World
public class Hello {
public static void main(String[] args) {
System.out.println("Hello Java World");
}
}
Hello World
>>>print "Hello Python World"
Hello Python World
Hello World
>(print "Hello Scheme World")
“Hello Scheme World”
>
Our Courses and Goals
Our Students:
Very little programming experience
Bright
Enthusiastic
Our Courses and Goals
Learn Computer Science
Problem Solving
Patterns
Techniques
Algorithms
Data Structures
Prepare for Upper Level Courses
CS-1
Basic problem solving approaches.
Programming is presented as a notation
Want to encourage not frustrate
Practice Practice Practice
CS-2
Students are still beginners!
Classic Algorithms and Data Structures
Problem solving patterns
Analysis
CS-3
Software Design and Development
2 Parallel Tracks
Java
Exceptions
Interfaces
Inner Classes.
GUI and Event Driven Programming
Threading
Preparing Students for Upper Level CS
CS1
Case Studies
Accumulator
Iteration Over a
Collection of Objects
Nested Loops and
Functions
Conditionals
Classes
Python Data Model
Consistency!
1 + 2 == 3
A=1+2
(1).__add__(2) == 3
A
3
CS2
Case Studies
Insertion Sort
(Pseudocode)
Insertion-Sort(A)
for j  2 to length[A]
key  A[j]
i  j - 1
while i > 0 and A[i] > key
A[i+1]  A[i]
i  i - 1
A[i + 1]  key
Insertion Sort
(Python)
def insertionSort(A):
for j in range(1,len(A)):
key = A[j]
i = j
while i>0 and A[i-1]>key:
A[i]=A[i-1]
i = i-1
A[i]=key
Comparing Python to
Pseudocode
Insertion-Sort(A)
for j  2 to length[A]
key  A[j]
i  j - 1
while i > 0 and A[i] > key
A[i+1]  A[i]
i  i - 1
A[i + 1]  key
def insertionSort(A):
for j in range(1,len(A)):
key = A[j]
i = j
while i>0 and A[i-1]>key:
A[i]=A[i-1]
i = i-1
A[i]=key
Running and Testing
cray:MICS2005> python -i insertion.py
>>> A = [9, 4, 2, 10, 7, 22, 1]
>>> insertionSort(A)
>>> A
[1, 2, 4, 7, 9, 10, 22]
>>> B = ['dog', 'cat', 'ape', 'eel']
>>> insertionSort(B)
>>> B
['ape', 'cat', 'dog', 'eel']
>>> C = [3.14, 2.78, 9.80, 3.8]
>>> insertionSort(C)
>>> C
[2.78, 3.14, 3.8, 9.8]
>>>
Sorting Objects
class student:
def __init__(self,lname,fname,gpa):
self.fname = fname
self.lname = lname
self.gpa = gpa
def __cmp__(self,other):
if self.gpa < other.gpa:
return -1
elif self.gpa == other.gpa:
return 0
else:
return 1
Knights Tour
20
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15
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15
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12
10
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5
6
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13
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9
5
9
1
0
1
2
3
4
3
Graph
class Graph:
def __init__(self):
self.vertList = {}
self.numVertices = 0
def addVertex(self,key):
self.numVertices = self.numVertices + 1
newVertex = Vertex(key)
self.vertList[key] = newVertex
return newVertex
def addEdge(self,f,t,cost=0):
if not self.vertList.has_key(f):
nv = self.addVertex(f)
for node in graph:
if not self.vertList.has_key(t):
print node.color
nv = self.addVertex(t)
self.vertList[f].addNeighbor(self.vertList[t],cost)
def __iter__(self):
return self.vertList.itervalues()
Vertex
class Vertex:
def __init__(self,num):
self.id = num
self.adj = []
self.color = 'white'
self.dist = sys.maxint
self.pred = None
self.disc = 0
self.fin = 0
self.cost = {}
def addNeighbor(self,nbr,cost=0):
self.adj.append(nbr)
self.cost[nbr] = cost
Depth First Search
def knightTour(n,path,u,limit):
u.setColor('gray')
orderByAvail(u)
path.append(u)
if n < limit:
nbrList = u.getAdj()
i = 0
done = False
while i < len(nbrList) and not done:
if nbrList[i].getColor() == 'white':
done = knightTour(n+1,path,nbrList[i],limit)
i = i + 1
if not done: # prepare to backtrack
path.remove(u)
u.setColor('white')
else:
done = True
return done
Complete Tour
CS3
Case Studies
First Few Weeks
2 weeks Java Basics (Using Collections)
Command Line then IDE
Building Classes
Testing -- jUnit
Interfaces and Inheritance
River Crossings
Graph
class Graph:
def __init__(self):
self.vertList = {}
self.numVertices = 0
public class Graph implements Iterable<Vertex> {
public Graph() {
this.vertList = new HashMap<Integer,Vertex>();
this.numVertices = 0;
}
private HashMap<Integer,Vertex> vertList;
private int numVertices = 0;
addVertex
def addVertex(self,key):
self.numVertices = self.numVertices + 1
newVertex = Vertex(key)
self.vertList[key] = newVertex
return newVertex
public Vertex addVertex(int key) {
this.numVertices = this.numVertices + 1;
Vertex newVertex = new Vertex(key);
this.vertList.put(key,newVertex);
return newVertex;
}
Iteration
def __iter__(self):
return self.vertList.itervalues()
for (Vertex v : g) {
System.out.println(node.color);
}
public Iterator<Vertex> iterator() {
return vertList.values().iterator();
}
Event Driven
Programming
Java Swing
Java 2D Graphics Programming
Model View Controller Pattern
Listeners and Event Handling
Pong
What is left?
Swing components
Threading
Simple Network Programming
Source Control
Database Access (JDBC)
XML
Next Project jPhoto
Summary
Put the focus back on Computer Science and
Problem Solving
By Using Python early we can:
Solve interesting problems that motivate
Learn important problem solving patterns
By Moving to Java at the right time we can:
Prepare students for success
encourage good software development
habits
[In a programming language]
Simple things should be simple
and complex things should be
possible. (Alan Kay)