can't call method in java

Question

I have a very stupid problem that's giving me a major headache.

I defined a method which searches an ArrayList to find a zipcode:

    public ZipCode findZip (int zip) {
       ZipCode aZip = new ZipCode(0);
       for(int i = 0; i < zips.size(); i++) {
          if(zips.get(i).getZipCode() == zip)
             aZip = zips.get(i);
          else
             aZip = null; }
       return aZip; }

...But, I cannot call it for the life of me. It gives me the "cannot find symbol" error every time I call it, no matter what object I use or parameter I input.

The entire program so far (it can't be finished until I figure this out):

import java.util.*;
import java.io.*;
import java.lang.Math;
public class ZipCodeDatabase {
    //Field
    private ArrayList<ZipCode> zips;

   //Constructor
   public ZipCodeDatabase () {
      zips = new ArrayList<ZipCode> (); 
   }

   //Mutator Method
   public void readZipCodeData(String filename) {
      Scanner inFS = null; 
      FileInputStream fileByteStream = null;
      try{
        // open the File and set delimiters
         fileByteStream = new FileInputStream("zipcodes.txt");
         inFS = new Scanner(fileByteStream);
         inFS.useDelimiter("[,\r\n]+");
       // continue while there is more data to read
         while(inFS.hasNext()) {
           //read in all input
            int aZip = inFS.nextInt();
            String aCity = inFS.next();
            String aState = inFS.next();
            double aLat = inFS.nextDouble();
            double aLon = inFS.nextDouble();
           //Create and add new zipcode
            ZipCode newZip = new ZipCode(aZip, aCity, aState, aLat, aLon);
            zips.add(newZip);
         }
         fileByteStream.close();
         // Could not find file
         }catch(FileNotFoundException error1) {
            System.out.println("Failed to read the data file: " + filename);
          // error while reading the file                      
         }catch(IOException error2) {
             System.out.println("Oops! Error related to: " + filename);
      }        
   }

   //Accessor Methods
   public ZipCode findZip (int zip) {
      ZipCode aZip = new ZipCode(0);
      for(int i = 0; i < zips.size(); i++) {
         if(zips.get(i).getZipCode() == zip)
            aZip = zips.get(i);
         else
            aZip = null;
      }
      return aZip;
   }
   public int distance(int zip1, int zip2) {
      int dist = 0;
      double p1 = 0.0;
      double p2 = 0.0;
      double p3 = 0.0;
      if(zips.findZip(zip1) == null || zips.findZip(zip2) == null)
         dist = -1;
...

The error itself is:

cannot find symbol - Method findZip(int)

You are using a symbol here which has not been declared in any visible scope.

Using ZipCodeDatabase.findZip(int); gives the following compiler error:

non-static method findZip(int) cannot be referenced from a static context

You are trying to reference an instance field or instance method from a static method.

I'm currently working through this, get back with more updates if needed. Thank you for all given help.

---

ZipCode itself isn't really in play for this issue, its just a bunch of set and get methods for the zips.

Answer 1

The problem comes from this line:

if(zips.findZip(zip1) == null || zips.findZip(zip2) == null)

Going up to the top of your class, we find the declaration of zips, which is

private ArrayList<ZipCode> zips;

This is a problem, because your findZip method is on the ZipCodeDatabase class, not on ArrayList. Since that call is happening from inside of a non-static method of ZipCodeDatabase, you can simply remove the object you're calling it on.

if(findZip(zip1) == null || findZip(zip2) == null)

This is equivalent to using

if(this.findZip(zip1) == null || this.findZip(zip2) == null)

which calls the method on the current instance of the ZipCodeDatabase class.