Re: Extracting data elements from a user-defined class stored in an ArrayList

Subject: Re: Extracting data elements from a user-defined class stored in an ArrayList

From: Joseph Broghamer <email@hidden>

Date: Fri, 9 Nov 2007 20:02:29 -0500

Delivered-to: email@hidden

Greg,

I copied your code to a new project in NetBeans and it worked fine.

You confirmed the correctness of my syntax to extract a data field from an element in the ArrayList:

System.out.println ( personArrayList.get(0).getFirstName() );

However, your code differs from mine in that I have a separate class with methods to load and print the ArrayList.

My project is made up of three classes:

            DataInputDem    (GUI display)
            Person   (defines data fields for a person and set and set methods)
     PersonQueries (manipulates the data for ArrayList and future MySQL)

Method insertNewPerson in class PersonQueries loads the ArrayList from the object newPerson:

public static int printArrayList (Person newPerson, ArrayList personArrayList)

Method printArrayList in class PersonQueries prints the ArrayList:

public static void printArrayList(ArrayList personArrayList)

The statement “System.out.println ( personArrayList.get(0).getFirstName() );”

works fine in the class DataInputDemo where the ArrayList is instantiated but not in the printArrayList method.

I don’t understand what is happing. It appears that the ArrayList is being loaded correctly from the newPerson object in method insertNewPerson and that the ArrayList is being passed correctly to the method printArrayList, but none of the methods are found.

Below is a copy of the error message I am getting:

Created dir: /Users/broghamerjt/MyJavaProjects/DataInputDemo/build/classes

Compiling 3 source files to /Users/broghamerjt/MyJavaProjects/DataInputDemo/build/classes

/Users/broghamerjt/MyJavaProjects/DataInputDemo/src/datainputdemo/PersonQueries.java:85: cannot find symbol

symbol : method getFirstName()

location: class java.lang.Object

+ personArrayList.get(0).getFirstName());

Note: /Users/broghamerjt/MyJavaProjects/DataInputDemo/src/datainputdemo/PersonQueries.java uses unchecked or unsafe operations.

Note: Recompile with -Xlint:unchecked for details.

1 error

BUILD FAILED (total time: 1 second)

Below is the source code for the PersonQueries class with error statement marked in read:

* PersonQueries.java

* Created on November 5, 2007, 11:29 PM

* This class accesses data structures

* to store records of type person

* in ArrayList

* and

* in MySQL Database (not yet implemented)

* Author: Joseph T. Broghamer

package datainputdemo;

import java.util.ArrayList;

import javax.swing.JFrame;

import javax.swing.JOptionPane;

public class PersonQueries

{

// No-arguments Constructor

public PersonQueries()

{

System.out.println ("From class constructor in PersonQueries");

} // end no-arguments constructor PersonQueries

public static int insertNewPerson(Person newPerson, ArrayList personArrayList)

{

int insertresult = 0; // used to determine if adding object (record) to ArrayList worked

// not currently implemented

System.out.println ("Printing out contents of parameter newPerson ");

System.out.println ("to ensure object data fields are correctly populated \n");

System.out.println (" " + newPerson.getFirstName());

System.out.println (" " + newPerson.getLastName());

System.out.println (" " + newPerson.getMiddleInitial());

System.out.println (" " + newPerson.getTelephoneNumber());

System.out.println (" " + newPerson.getApartmentSuite());

System.out.println (" " + newPerson.getCityName());

System.out.println (" " + newPerson.getStateName());

System.out.println (" " + newPerson.getzipCodeName());

System.out.println ();

System.out.println ("From method insertNewPerson, "

+ "adding newPerson to personArrayList \n");

personArrayList.add(newPerson);

System.out.println (" ArrayList index = " + personArrayList.indexOf(newPerson));

System.out.println ();

System.out.println (personArrayList.get(0));

System.out.println ();

// Print contents of ArrayList to scrollTextArea of GUI

// Not currently implemented

return insertresult;

} // end method insertNewPerson

public static void printArrayList(ArrayList personArrayList)

{

System.out.println (" From method printArraylist");

System.out.println ("Value for personArrayList.get(0) = " + personArrayList.get(0));

System.out.println ("From class DataInputDemo, personArrayList.get(0).getFirstName()) = "

+ personArrayList.get(0).getFirstName());

} // end method printArraylist

} // end class PersonQueries

On Nov 9, 2007, at 12:42 AM, Greg Guerin wrote:

Joseph Broghamer wrote:

Using the NetBeans debugger I was able to confirm that the data does exist
in ArrayList element zero (0). However, when I try to extract a data
element from the class with a the following statement:

System.out.println (personArrayList.get(0).getFirstName());

I get the 'cannot find symbol' error during compile.

Please copy and paste the exact error you you get into an email, and post
it to the list. There can be any number of different symbols that aren't
being found, and what isn't found tells a lot about what's wrong.
Paraphrasing errors is vague; accuracy matters.

The following isolated test-case works for me. If it doesn't compile or
run correctly for you, please copy and paste any errors you get into an
email, and post to the list.

If the following works, then I suggest making your own test-case from your
original code, perhaps by removing things until it works, then adding
things back until it breaks.

import java.util.*;

public class Lister
{
public static void main( String[] args )
{
   ArrayList <Person> personArrayList = new ArrayList<Person>();

   Person newPerson = new Person( "Arnold", "Rimmer" );

   personArrayList.add( newPerson );

   System.out.println( "Value for personArrayList.get(0) = " +
personArrayList.get(0) );
   System.out.println( personArrayList.get(0).getFirstName() );
}
}

class Person
{
private String first, last;

public Person( String first, String last )
{ this.first = first; this.last = last; }

public String getFirstName()
{ return first; }

public String getLastName()
{ return last; }

public String toString()
{ return "Hi, I'm " + getFirstName() + " " + getLastName(); }
}

-- GG

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References:
	>Re: Extracting data elements from a user-defined class stored in an ArrayList (From: Greg Guerin <email@hidden>)