Question

Write a program that reads a Java source file and produces an index of all identifiers in the file. For each identifier, print all lines in which it occurs. For simplicity, we will consider each string consisting only of letters, numbers, and underscores an identifer. Declare a Scanner in for reading from the source file and call in.useDelimiter("[^AZa-z0-9_]+"). Then each call to next returns an identifier.

Java. Explain logic used lease.

Answer 1

IdentifierIndex.java

/**
A class to read in a Java source file and
produce an index of all identifiers in the file.
*/

. . .

public class IdentifierIndex
{
. . .

/**
Reads all identifiers from the given file
@param filename the file name
*/
public void read(String filename) throws FileNotFoundException
{
. . .
}

/**
A set of all identifiers that occur in the file, in sorted order.
*/
public Set<String> getIdentifiers()
{
. . .
}

/**
Gets all line numbers on which the given identifier occurs.
@param identifier an identifier
@return all line numbers on which the identifier was found, in increasing
order; an empty set (not null) if the identifier was never found
*/
public Set<Integer> getLines(String identifier)
{
. . .
}
}

IndexDemo.java

import java.io.FileNotFoundException;
import java.util.Set;

/**
   A program to read in a Java source file and
   produce an index of all identifiers in the file.
*/
public class IndexDemo
{  
   public static void main(String[] args)
      throws FileNotFoundException
   {  
      IdentifierIndex index = new IdentifierIndex();
      index.read("IndexDemo.java"); // reads this file
      Set<String> idents = index.getIdentifiers();
      for (String ident : idents)
      {
         Set<Integer> lines = index.getLines(ident);
         System.out.println(ident + ": " + lines);
      }
   }
}

IndexTester.java

import java.io.FileNotFoundException;
import java.util.Iterator;
import java.util.Set;

public class IndexTester
{  
   public static void main(String[] args)
      throws FileNotFoundException
   {  
      IdentifierIndex index = new IdentifierIndex();
      index.read("IndexTester.java"); // reads this file
      Set<String> idents = index.getIdentifiers();
      String last = "";
      for (String s : idents) { last = s; }
      System.out.println(last); // The last identifier
      System.out.println("Expected: void");
      Set<Integer> lines = index.getLines("void");
      System.out.println(lines);
      System.out.println("Expected: [7, 16, 17]");
      System.out.println(index.getLines("f" + "oo"));
      System.out.println("Expected: []");
   }
}