Complete Program

After playing with the test program a while to check that things work you can write the complete program:

import java.util.* ;
import java.io.*;

class Entry
{
  String name;
  String number;

  // constructor
  Entry( String n, String num )
  {
    name = n; number = num;
  }

  // methods
  public boolean equals( Object other )
  {
    return name.equals( ((Entry)other).name );
  }

  public String toString()
  {
    return "Name: " + name + " Number: " + number;
  }
 
}

class PhoneBookAp
{
  public static void main ( String[] args) throws IOException
  {
    Vector phone = new Vector( 10 );

    phone.addElement( new Entry( "Amy", "123-4567") );
    phone.addElement( new Entry( "Bob", "123-6780") );
    phone.addElement( new Entry( "Hal", "789-1234") );
    phone.addElement( new Entry( "Deb", "789-4457") );
    phone.addElement( new Entry( "Zoe", "446-0210") );

    String name;
    BufferedReader stdin = new BufferedReader(
      new InputStreamReader( System.in ) );

    System.out.print("Enter name -->");
    name = stdin.readLine().trim();

    while( !name.equals("quit" ) )
    {
      int spot = phone.indexOf( new Entry( name, "") ) ;

      if ( spot >= 0 )
        System.out.println( phone.elementAt( spot ) ) ;
      else
        System.out.println( name + " not found" ) ;

      System.out.print("Enter name -->") ;
      name = stdin.readLine().trim() ;
    }
 
  }
}

Of course, this is a small example and not a practical program. But the techniques it uses are used in many industrial-strength programs. Carefully examine:

1. How a Vector of user-defined objects is used.
2. How the equals() method is written.
   • It needs to override the inherited method for the indexOf() method to work.
   • Type casting must be used inside the method.
3. Use of the indexOf() method to search the vector.
   • A "target" object is constructed for use with the indexOf() method.

You may regard all this as more bother than it is worth, since the previous "phone book" example worked fine using a plain array. But in large programs a linear arrangement of data is so common, and the operations on it are so frequent, that the Vector class is a worthwhile time saver.