Sahami
CS Mehran 106A
Handout #30A
November 2, 2011
Solution to Section #5
Portions of this handout by Eric Roberts
1. Word count
/*
* File: WordCount.java
* -------------------* Counts the characters, words, and lines in a file.
*/
import acm.program.*;
import java.io.*;
public class WordCount extends ConsoleProgram {
public void run() {
int lines = 0;
int words = 0;
int chars = 0;
BufferedReader rd = openFileReader("File: ");
try {
while (true) {
String line = rd.readLine();
if (line == null) break;
lines++;
words += countWords(line);
chars += line.length();
}
rd.close();
} catch (IOException ex) {
println("An I/O exception has occurred");
}
println("Lines = " + lines);
println("Words = " + words);
println("Chars = " + chars);
}
/**
* Asks the user for the name of an input file and returns a
* BufferedReader attached to its contents. If the file does
* not exist, the user is given another chance to try.
*/
private BufferedReader openFileReader(String prompt) {
BufferedReader rd = null;
while (rd == null) {
String name = readLine(prompt);
try {
rd = new BufferedReader(new FileReader(name));
} catch (IOException ex) {
println("Can't open that file.");
}
}
return rd;
}
2
/**
* Counts the words (consecutive strings of letters and/or digits)
* in the input line.
*/
private int countWords(String line) {
boolean inWord = false;
int words = 0;
for (int i = 0; i < line.length(); i++) {
char ch = line.charAt(i);
if (Character.isLetterOrDigit(ch)) {
inWord = true;
} else {
if (inWord) words++;
inWord = false;
}
}
if (inWord) words++;
return words;
}
}
2. How Unique!
/*
* File: UniqueNames.java
* ---------------------* This program asks the user for a list of names (one per line)
* until the user enters a blank line. Then the program prints
* out the list of names entered, where each name is listed only
* once (i.e., uniquely)
*/
public class UniqueNames extends ConsoleProgram {
public void run() {
ArrayList<String> list = new ArrayList<String>();
while (true) {
String name = readLine("Enter name: ");
if (name.equals("")) break;
if (!list.contains(name)) {
list.add(name);
}
}
println("Unique name list contains:");
printList(list);
}
/* Prints out contents of ArrayList, one element per line */
private void printList(ArrayList list) {
for(int i = 0; i < list.size(); i++) {
println(list.get(i));
}
}
}
3
3. A Christmas Carol
/**
* File: Employee.java
* ---------------------* Class which describes the Employee variable type.
*/
public class Employee {
public Employee(String newName, int newId) {
name = newName;
taxId = newId;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public boolean isActive() {
return active;
}
public void setActive(boolean active) {
this.active = active;
}
public int getSalary() {
return salary;
}
public void setSalary(int salary) {
this.salary = salary;
}
public String getName() {
return name;
}
public int getTaxId() {
return taxId;
}
/* Employee instance variables */
String name;
int taxId;
String title;
boolean active;
int salary;
}
4
/**
* File ChristmasCarol.java
* -----------------------* Counts the words (consecutive strings of letters and/or digits)
* in the input line.
*/
public class ChristmasCarol ConsoleProgram{
public extends void run() {
Employee ceo = new Employee(Ebenezer Scrooge, 161803399);
Employee partner = new Employee(Jacob Marley, 271828182);
Employee clerk = new Employee(Bob Cratchit, 314159265);
ceo.setTitle(Ceo);
partner.setTitle(Former Partner);
clerk.setTitle(Clerk);
ceo.setActive(true);
partner.setActive(false);
clerk.setActive(true);
ceo.setSalary(1000);
partner.setSalary(0);
clerk.setSalary(25);
}
}
}
4. Histogram
/*
* File: Histogram.java
* -------------------* This program reads a list of exam scores, with one score per line.
* It then displays a histogram of those scores, divided into the
* ranges 09, 1019, 2029, and so forth, up to the range containing
* only the value 100.
*/
import acm.program.*;
import acm.util.*;
import java.io.*;
public class Histogram extends ConsoleProgram {
public void run() {
initHistogram();
readScoresIntoHistogram();
printHistogram();
}
/* Initializes the histogram array */
private void initHistogram() {
histogramArray = new int[11];
for (int i = 0; i <= 10; i++) {
histogramArray[i] = 0;
}
}
5
/* Reads the exam scores, updating the histogram */
private void readScoresIntoHistogram() {
try {
BufferedReader rd
= new BufferedReader(new FileReader(DATA_FILE));
while (true) {
String line = rd.readLine();
if (line == null) break;
int score = Integer.parseInt(line);
if (score < 0 || score > 100) {
throw new ErrorException("That score is out of range");
} else {
int range = score / 10;
histogramArray[range]++;
}
}
} catch (IOException ex) {
throw new ErrorException(ex);
}
}
/* Displays the histogram */
private void printHistogram() {
for (int range = 0; range <= 10; range++) {
String label;
switch (range) {
case 0: label = "00-09"; break;
case 10: label = " 100"; break;
default:
label = (10 * range) + "-" + (10 * range + 9);
break;
}
String stars = createStars(histogramArray[range]);
println(label + ": " + stars);
}
}
/* Creates a string consisting of n stars */
private String createStars(int n) {
String stars = "";
for (int i = 0; i < n; i++) {
stars += "*";
}
return stars;
}
/* Private instance variables */
private int[] histogramArray;
/* Name of the data file */
private static final String DATA_FILE = "MidtermScores.txt";
}
6
5. Tracing method execution
The output of Halloween.java is:
skellington 10
Syle Focus for Section 5: Writing our Own Classes
In this section we wrote our own Employee class. In our class we wrote several getter
and setter methods. A getter method is one where we can access the value of a private
data member, and a setter method is where we provide access for the client to set the
value. We use getters and setters instead of making our instance variables public because
we do not want to give other classes direct access, or we may not want them changing
every variable. This is a common pattern in object-oriented programming.
You should also not the naming conventions we use suchg as getName(). This is a
standard way to name a getter method, where we write get and then the name of our
variable.
Another important part of the class is choosing the instance variables. What are the things
that define an Employee? Each one has its own name, salary, etc. These are usually the
instance variables.