Transcript Lec04-8 - UMass CS !EdLab

CS 121 – Intro to Programming:Java - Lecture 8
Announcements
Current Owl assignment is due Wednesday. Next Owl
assignment - arrays I - will be up by tomorrow morning
Programming assignment 5 is up, due next week. Hand in
protocol will be announced on-line tomorrow afternoon.
Late rules in effect - late programs are reduced in value by
half.
Preregistration coming - what should you take?
Get going on program five!
Here’s one thing you can do…the bouncing ball example..
Form your groups..
Email me your ideas, etc..
We’ve seen Java at two levels:
• the statement level - mechanisms for getting specific,
often low-level jobs, done, e.g. assignment stmts,
println, etc.
• the (class and) object level - mechanisms for
modeling things (objects) according to an” Objects”
(repositories of state) served by methods (machinery
for realizing behaviors) scheme
Now we’re back to a new and very important idea in
statement-level thinking: arrays.
Basically, arrays give us a new way to think about
variables.
Think about: students in a class; seats on an airplane, rooms in a motel,
positions in the deli line at a super-market.
In all cases:
• Many variables required for representation
• There’s an indexing scheme for locating / identifying the
variables in question
Student 7
Seat 23B
Room 201
Deli-line position 77
• some indexing schemes are more natural than others
• some are two-dimensional
public class ArrayTest1{
public static void main(String[] args)
{ int[] firstArray = new int[10];
for(int j = 0; j < 10; j++)
firstArray[j] = j*j;
System.out.println("here they come");
for(int j = 0; j < 10; j++)
System.out.println(firstArray[j]);
}
}
public class BasicArray {
final static int LIMIT = 15;
final static int MULTIPLE = 10;
public static void main (String[] args) {
int[] list = new int[LIMIT];
for (int index = 0; index < LIMIT; index++)
list[index] = index * MULTIPLE;
list[5] = 999; // change one array value
for (int index = 0; index < LIMIT; index++)
System.out.print (list[index] + " ");
}
}
public class Test{
// all characters have a position in Unicode
// Ascii comes first : 0 - 127
// when an integer op is applied to a character, it
// is automatically converted into an integer
public static void main(String[] args){
int i,j;
i = (int) 'a'; j = (int) 'A';
System.out.println(i + " " + j);
System.out.println('a' - 'A');
System.out.println('e' - 'a');
}
}
´œ ----jGRASP exec: java Test
œœßœ97 65
œœßœ32
œœßœ4
public class LetterCount{
//----------------------------------------------------------------// Reads a sentence from the user and counts the number of
// uppercase and lowercase letters contained in it.
//----------------------------------------------------------------public static void main (String[] args) {
ConsoleWindow c = new ConsoleWindow(50,40, "my window");
final int NUMCHARS = 26;
int[] upper = new int[NUMCHARS];
int[] lower = new int[NUMCHARS];
char current; // the current character being processed
int other = 0; // counter for non-alphabetics
c.out.println ("Enter a sentence:");
String line = c.input.readLine(); // reads line
c.out.println("line length " + line.length());
// Count the number of each letter occurence
for (int ch = 0; ch < line.length(); ch++)
{
current = line.charAt(ch);
if (current >= 'A' && current <= 'Z')
upper[current-'A']++;
else
if (current >= 'a' && current <= 'z')
lower[current-'a']++;
else
other++;
}
// Print the results
c.out.println ();
for (int letter=0; letter < upper.length; letter++)
{
c.out.print ( (char) (letter + 'A') );
c.out.print (": " + upper[letter]);
c.out.print ("\t\t" + (char) (letter + 'a') );
c.out.println (": " + lower[letter]);
}
c.out.println ();
c.out.println ("Non-alphabetic characters: " + other);
}
}
We’re going to write an application that rolls a
pair of dice 10000 times and reports the results
profile of the rolls (e.g. how many 2,3, etc came
up.
public class DiceTester{
public static void main(String[] args){
Dice d = new Dice();
d.multiToss(10000);
d.showScoreboard();
}
}
import java.util.Random;
public class Dice{
Random r;
int[] scoreboard = new int[13];
public Dice(){
r = new Random();
initializeScoreboard();
}
public void initializeScoreboard(){
for(int j = 0; j < 13; j++) scoreboard[j] = 0;}
public int tossDie(){
return (1+r.nextInt(6));
}
public int throwDice(){
return(tossDie() + tossDie());
}
public void multiToss(int tossCount){
int score;
for (int j = 0; j < tossCount; j++){
score = throwDice();
scoreboard[score]++;
}
}
public void showScoreboard(){
for(int j = 2; j < 13; j++)
System.out.println("toss of " + j + " " + scoreboard[j]);
}
Results:
œœœ
œœ´œ ----jGRASP exec: java DiceTester
œœßœtoss of 2
303
œœßœtoss of 3
543
œœßœtoss of 4
807
œœßœtoss of 5
1123
œœßœtoss of 6
1432
œœßœtoss of 7
1630
œœßœtoss of 8
1389
œœßœtoss of 9
1129
œœßœtoss of 10 808
œœßœtoss of 11 557
œœßœtoss of 12 279
œœßœ
œœ©œ ----jGRASP
import element.*;
public class PolyTester{
public static void main(String[] args){
ConsoleWindow c = new ConsoleWindow();
DrawingWindow d = new DrawingWindow(500,200);
Pt[] poly = new Pt[5];
int x, y;
c.out.println("enter 5 pts - 10 ints - separated by CRs");
for(int j = 0; j < 5; j++) {
x = c.input.readInt();
y = c. input.readInt();
poly[j] = new Pt(x,y); }
for(int j = 1; j < 5; j++) {
L = new Line(poly[j-1], poly[j]);
L.drawOn(d); }
L = new Line(poly[4],poly[0]); // final connector
L.drawOn(d);
}