ArrayList question (Java)

ksgill · 10-13-2003, 06:53 PM

I am trying to write a code where values are read via commandline arguments and stored as strings in an ArrayList (with no duplicates).

Code:

public static void main(String argv[]) throws IOException {
    BufferedReader br = new BufferedReader(
               new InputStreamReader(System.in));
    String courseName;
    ArrayList names= new ArrayList();
    String s= br.readLine();
    while( s != null) {
      StringTokenizer st= new StringTokenizer(s);

      while (st.hasMoreElements()) {
          courseName= st.nextToken();
          A3 a= new A3(courseName, numPrereq);
          if (!names.contains(a)) names.add(a);
          else continue;
      }
        s= br.readLine();
      }

But, the output I get contains duplicates...can someone point to me what I am doing wrong?

nephilim · 10-14-2003, 03:05 AM

I tried your sample code adding a simple String to the ArrayList (because I don't know what object A3 does), and it works... No duplicates are added to the ArrayList.

Is it possible that the A3 object makes them different?

ksgill · 10-14-2003, 09:38 AM

here is the complete code:

Code:

 
public static void main(String argv[]) throws IOException {
    BufferedReader br = new BufferedReader(
               new InputStreamReader(System.in));
    String courseName;
    ArrayList names= new ArrayList();
    String s= br.readLine();
    while( s != null) {
      StringTokenizer st= new StringTokenizer(s);

      while (st.hasMoreElements()) {
          courseName= st.nextToken();
          A3 a= new A3(courseName);
          if (!names.contains(a)) names.add(a);
          else continue;
      }
        s= br.readLine();
      }
                                                                                
   for (int num= 0; num< names.size(); num++) {
   System.out.println(names.get(num));
  }
 }
}

Testdata:
CS1101 CS1100
Ma1010 Ma1000
CS2132 CS1100
CS3132 CS2132
CS3132 CS2140

here is the output that I get:
CS1101:
CS1100:
Ma1010:
Ma1000:
CS2132:
CS1100:
CS3132:
CS2132:
CS3132:
CS2140:

ksgill · 10-14-2003, 09:39 AM

this is the code for main class:

Code:

import java.util.*;
import java.io.*;
public class A3 {
  String course;  //name of the course
                                                                                
  public A3(String s) { // class constructor
  course= s;
  }
  public String toString() {  // println method
        return course+ ": "  ;
 }

Sorry I made a mistake in copy pasting in my earlier post

glj · 10-14-2003, 10:03 AM

I'm not eintrely sure if this is true but maybe because you've created instances of A3 even though they may have the same attributes, they are seen as different because they are two different and distinct instances.
Maybe you should test for equality before creating an instance of A3 i.e. check if courseName exists in names, and then decide on whether or not to create a new A3.

Does that make sense? :S

glj

ksgill · 10-14-2003, 02:00 PM

yea..i think it makes sense glj. I will give it a try