Thread: Reading txt

Comparable is not a class but an interface. That means you implement it for the City class to provide a way of comparing one City instance to another. When you implement an interface you need to provide the code for the method signatures specified in the interface declaration. Check out the Java tutorial in my signature on interfaces. Also check out the Java API for the comparable interface description.

Regards,
Jim

how to read from a file or put things from a file into an array.

Look at using the Scanner class's methods to read from the file.

A problem with using an array is that the array must be defined large enough to hold all the data that will be read.
An ArrayList would not have that problem.

Here's one approach.

1. Create a City class as described.
2. Then populate an instance via the constructor with a city and zipcode.
3. Override toString to print the city and zipcode or include a separate method do do that.

Once you have that working, focus on reading in the file and creating an instance for each city/zipcode combination.
Print them out to see if they work.

Then implement the required interface.

The point is break up the task into small pieces that you can complete, debug, and then forget about. It makes things much easier.

Regards,
Jim

Why are you using a TreeMap? That is not necessary to sort a list of items. The assignment says,

Notice: We expect you to use one of the predefined sorting algorithms in the Java class library when sorting the cities.

Did you check out Arrays.sort or Collections.sort?

Regards,
Jim

Are you saying you have two arrays? If so, why?

I think you missed the point of the assignment. My take was to create a City class and put the name and the zipcode as fields in that class. The class should implement the Comparable interface so you can then sort the class on the zipcode. You do not need two arrays to do that.

Note also that you can set the delimiter in the Scanner class and then use the appropriate Scanner methods to get the values so you don't have to split the line. But your way of doing that also works.

Regards,
Jim

You have way too much stuff in there and most of it unnecessary. Just create a City class with two fields, an int zipcode field and a String name field. You can assign these via a constructor. Also include a toString method to return a String to print as described in the assignment. This class should be less than 20 lines of code.

Regards,
Jim

Originally Posted by jim829

You have way too much stuff in there and most of it unnecessary. Just create a City class with two fields, an int zipcode field and a String name field. You can assign these via a constructor. Also include a toString method to return a String to print as described in the assignment. This class should be less than 20 lines of code.

Regards,
Jim

I see what you mean jim but why would i need a constructor? If i used a constructor then wouldn't i need to read the file from the main before even going into the city class?

The constructor is used to populate the class with certain values (also referred to as state). You read in the values of the file and while you do you create a City instance and place it in an a list.

Assume you are in your MainClass and you have another class defined called City.

while there is input from the scanner
     read zipcode
     read name
     City c = new City(name, zipcode)
     add c to list
end

Regards,
Jim

Okay so i think that i might be close now.

However i have gotten into a problem.
Cannot use constructors within the interface.
I have tested without the interface all together and it works fine.

Main :

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Collections;
 
public class cityMain {
 
	private static BufferedReader r;
 
	public static void main(String[] args) {
		int Z = 0;
		String C = null;
		try {
			ArrayList<City2> City = new ArrayList<City2>();
 
			FileReader file = new FileReader("C:\\Users\\me\\Desktop\\BB.dat");
			r = new BufferedReader(file);
			 String currLine;
			while ((currLine = r.readLine()) != null) {
 
				if (currLine.trim().length() > 0) {
					String[] split = currLine.split(";");
					Z = (Integer.parseInt(split[0]));
					C = (split[1]);
					City.add(new City2(Z, C));
				}
			}
			Collections.sort(City, (c1, c2) -> c1.getZipCode() - c2.getZipCode());
 
			for (int i = 0; i < City.size(); i++) {
				System.out.println(City.get(i).getZipCode() + " " + City.get(i).getCityName());
 
			}
 
		} catch (IOException e) {
			System.out.println("Erorr : " + e);
		}
 
	}
 
}

City :

public class City2 implements Comparable {
 
	private int zipCode;
	private String cityName;
 
	public City2(int zipCode, String cityName) {
		this.zipCode = zipCode;
		this.cityName = cityName;
	}
 
	public int getZipCode() {
		return zipCode;
	}
 
	public String getCityName() {
		return cityName;
	}
 
}

And Comparable :

public interface Comparable {
 
        City2(int zipCode, String cityName);    //<--- doesn't like this... 
 
 	public int getZipCode();
 
	public String getCityName();
 
}

Ideas?

You should not be defining the Comparable interface. That is already defined in the Java SE classes.
When a class implements an interface, it needs to define the methods of the interface.
Look at the API doc for Comparable to see what methods are required.
http://docs.oracle.com/javase/8/docs/api/index.html

Originally Posted by Norm

You should not be defining the Comparable interface. That is already defined in the Java SE classes.
When a class implements an interface, it needs to define the methods of the interface.
Look at the API doc for Comparable to see what methods are required.
http://docs.oracle.com/javase/8/docs/api/index.html

Well i thought that it was going so? "it need so define the methods of the interface" but its doing so?
I am so lost haha.

Take a look at the tutorial: https://docs.oracle.com/javase/tutor...interface.html

Your code should use the definition of Comparable provided in the java SE classes. You should not define the interface yourself.

Originally Posted by Norm

Take a look at the tutorial: https://docs.oracle.com/javase/tutor...interface.html

Your code should use the definition of Comparable provided in the java SE classes. You should not define the interface yourself.

Looking in the classes i found "Comparable<T>", so you're saying... that i should use that in my interface?

No. You do NOT define an interface. You are supposed to use the existing interface: Comparable.
The tutorial at the link I posted has an example of how to use an interface.

Originally Posted by Norm

No. You do NOT define an interface. You are supposed to use the existing interface: Comparable.
The tutorial at the link I posted has an example of how to use an interface.

Okay so... the interface is like the "laws" that other classes has to follow. And the mainClass is calling another class throughout the deals of the interface.

So from the mainClass it should look like this :

TheInterface SomeName = new TheClassThatShouldBbeyTheLawsOfOurInterface "Aka the class name" ();

And what i am doing is that i am calling the the class from the main directly... which i guess that i should not do.

So i should call another class from mainClass throughout the Interface to the class that i want the Interfaces rules to apply.
Hope i got that right...

The the example is just an interface with a class, and the class has all the methods that the interface told the class to have.

The Comparable interface defines a method that the sort method needs to be able to sort the collection of City objects. The sort method calls the interface's method to determine the ordering of two City objects.

Originally Posted by Norm

The Comparable interface defines a method that the sort method needs to be able to sort the collection of City objects. The sort method calls the interface's method to determine the ordering of two City objects.

Sorry but i am still lost... haha.

The tutorial shows an example. The Bicycle interface defines several methods. The ACMEBicycle class impletments that interface and provides definitions for the methods defined in the Bicycle interface. Now an instance of the ACMEBicycle class can be treated as a Bicycle allowing any other code to call any of the Bicycle interface's methods.

For your case, the City class must implement the Comparable interface and provide definitions for the method(s) in Comparable. Then the sort method which requires objects of type Comparable will call the methods to sort a collection of City objects.
Read the API doc for the Collections class's sort method. It says:

All elements in the list must implement the Comparable interface.

A commonly used interface is ActionListener. Have you used that? Look at the code for that.
Also see an example in the tutorial:
https://docs.oracle.com/javase/tutor...nlistener.html