2-1 cm0551 week 3 the scanner class – file input a spelling checker time and space requirements...
TRANSCRIPT
2-1
CM0551 Week 3
• The scanner class – file input
• A Spelling Checker
• Time and space requirements for various dictionary structures
2-2
Scanner class
• A standard Java class
• Can be used for keyboard input
• Part of JDK 1.5
• import java.util.Scanner;
• A simple text scanner which parses primitive types and strings
• Uses a delimiter pattern of whitespace to identify tokens
2-3
Example Program 1
import java.util.Scanner;
public class Example1
{
public static void main (String [] args)
{
Scanner myScanner = new Scanner( System.in );
String aLine = myScanner.nextLine();
System.out.println( aLine);
}
}
keyboard
2-4
Example Program 1 cont’
import java.util.Scanner;
// Tells Java to look for the Scanner class
Scanner myScanner = new Scanner( System.in );
// Declares a Scanner object called myScanner
String aLine = myScanner.nextLine();
// nextLine() is a method of the Scanner class
// it reads a line of text from the keyboard.
2-5
Some Scanner Methods
To read this Use this
A number with no decimal point
nextInt();
A number with a decimal point nextDouble();
A word ending in a blank space next();
A line ( or what remains of the line)
nextLine();
A single character findInLine(“.”).charAT(0);
2-6
Example Program 2
import java.util.Scanner;
public class Example2
{
public static void main (String [] args)
{
Scanner myScanner = new Scanner( System.in );
int anInt = myScanner.nextInt();
System.out.println( anInt);
}
}
2-7
Example Program 3
import java.util.Scanner;
public class Example3
{
public static void main (String [] args)
{
Scanner myScanner = new Scanner( System.in );
int anInt = myScanner.nextInt();
double aDouble = myScanner.nextDouble();
System.out.println( “The int was “+anInt);
System.out.println( “The double was “+aDouble);
}
}
2-8
Scanner class and file input
import java.util.*;
import java.io.*;
public class ReadAccs
{
public static void main(String [] args)
{
TreeSet accs = new TreeSet();
2-9
Scanner class and file input (2)
try
{
readAccounts
("D:\\DSA&DP\\w3\\studentAccs.txt", accs);
}
catch(IOException ioe)
{
System.out.println("Cannot open file");
System.exit(1);
}
System.out.println(accs);
}
2-10
Scanner class and file input (3)
public static void readAccounts(String filename, TreeSet accs)
throws IOException
{
Scanner sc = new Scanner(new FileReader(filename));
String accName;
while (sc.hasNext())
{
accName = sc.next();
accs.add(accName);
}
}
}
2-11
Data and results
• File studentAccs contains
p01234
p01235
p01236
p01237
p01238
p01239
p01240
Program output[p01234,p01235,p01236,p01237,p01238,p01239,p01240]
2-12
A simple spell checker methodpublic static void spellChecker() {
TreeSet dictionary = new TreeSet();Scanner dictFile = null, docFile = null;String word;try{ dictFile = new Scanner(new FileReader
("D:\\DSA&DP\\w3\\dict.txt")); docFile = new Scanner(new FileReader
("D:\\DSA&DP\\w3\\doc.txt"));}
2-13
A simple spell checker method (2)catch(IOException ioe){
System.out.println("Cannot open a file");System.exit(1);
}
while (dictFile.hasNext()){
word = dictFile.next();dictionary.add(word);
}
2-14
A simple spell checker method (3)
System.out.println ("The following words are not in the dictionary!");
while (docFile.hasNext()){
word = docFile.next();if (!dictionary.contains(word)){
System.out.println(word);}
}}
2-15
Time and space requirements for various dictionary structures
time (sec) space
Array and sequential search 57 714K
Linked list and sequential search 57 1.3M
Array (sorted) and binary search .04 714K
Binary search tree .04 1M
Two level packed tree .08 360K
Good data structure design is important
2-16
For next week
Complete this weeks exercises.
Next week we cover algorithms, so read up about them.