Thread: Reading txt

Originally Posted by Norm

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:


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

Will try it out and try to understand it better. Thanks Norm.

Have tried to use an actionlistener all night.

Nothing is working for me... even with all the damn youtube videos around, my books or the examples.
:/ Feel really lost.

Okay, let's make this simple. Here is an interface.

interface EvenOdd {
boolean isEven(int v);
}

Create a small class that implements the interface and returns either true if the integer is even or false if it is odd. To test it, simply call the method with a number.

The only difference structure wise between this and the Comparable interface is that the Comparable interface is provided by the JDK API so all you have to do is implement it.

In this case, I created it so you need to copy the EvenOdd declaration to your source file.

Regards,
Jim

Originally Posted by jim829

Okay, let's make this simple. Here is an interface.

interface EvenOdd {
boolean isEven(int v);
}

Create a small class that implements the interface and returns either true if the integer is even or false if it is odd. To test it, simply call the method with a number.

The only difference structure wise between this and the Comparable interface is that the Comparable interface is provided by the JDK API so all you have to do is implement it.

In this case, I created it so you need to copy the EvenOdd declaration to your source file.

Regards,
Jim

Okay so i made one main class, interface and the class that does everything for me :

main:

public class tets {
 
	public static void main(String[] args) {
		EvenOdd c = new small();
		System.out.println(c.isEven(3));
	}
 
}

interface:

interface EvenOdd {
	boolean isEven(int v);
 
}

class:

public class small implements EvenOdd {
 
	public boolean isEven(int v) {
		if (v % 2 == 0) {
		return true;
		}
		return false;
	}
 
}

This kinda makes sense but my own code doesn't make sense haha.

And also, been looking at the comparable from java.
It has it's own method yet i don't know how to use it nor do i know
if i should call all my methods from "TheMainCity" --> "Interface" --> "CityImplementedWithComparable".

Here's another example:

import java.util.*;
 
public class InterfaceExample {
   // Define the interface with a method
   interface TalkToMe {
      public void speak();   
   }
 
   // Define some classes that implement the interface
   class Dog implements TalkToMe {
      public void speak() {
         System.out.println("bow wow");
      }
   }
   class Cat implements TalkToMe {
      public void speak() {
         System.out.println("Meow");
      }
   }
   class Bird implements TalkToMe {
      public void speak() {
         System.out.println("Tweet");
      }
   }
 
   //-------------------------------------------------------
   InterfaceExample() {
      // Define a list to hold objects that implement the TalkToMe interface
      List<TalkToMe> ttmList = new ArrayList<>();    
      Cat cat = new Cat();
      ttmList.add(cat);
      TalkToMe ttm = new Dog();
      ttmList.add(ttm);
      ttmList.add(new Bird());
 
      // iterate the list and call the interface's method
      for(TalkToMe x : ttmList) {
         callSpeak(x);
      }
   }
 
   //  Handle TalkToMe objects
   void callSpeak(TalkToMe ttm) {
      ttm.speak();
   }
 
   public static void main(String[] args) {
      new InterfaceExample();
   }
}

Think that i got this now:

Main:

import java.io.BufferedReader;
import java.io.FileReader;
import java.io.IOException;
import java.util.ArrayList;
import java.util.Comparator;
 
public class cityMain {
	private static BufferedReader r;
	public static ArrayList<City2> City = new ArrayList<City2>();
 
	public static void main(String[] args) {
		int Z = 0;
		String C = null;
		try {
			FileReader file = new FileReader("C:\\Users\\karwa\\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]);
				}
				City2 d = new City2(Z, C);
				City.add(d);
			}
 
			City.sort(Comparator.comparing(City2::getZipCode));
			for (int i = 0; i < cityMain.City.size(); i++) {
				System.out.println(cityMain.City.get(i).getZipCode() + " " + cityMain.City.get(i).getCityName());
			}
 
		} catch (IOException e) {
			System.out.println("Erorr : " + e);
		}
 
	}
 
}

City2:

public class City2 implements Comparable<City2> {
 
	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;
	}
 
	@Override
	public int compareTo(City2 city) {
		return this.getZipCode() - city.getZipCode();
	}
 
}

I get the correct answers back and using the "compareTo" method.

public static ArrayList<City2> City = new ArrayList<City2>();

Variable names should begin with a lowercase letter: city vs City
The name of a list should reflect what is in the list. cities would be a list of cities, city is singular and does not represent a list.

using the "compareTo" method.

Are you sure that method is ever used or called? Add a print statement to show that it is executed.

Originally Posted by Norm

public static ArrayList<City2> City = new ArrayList<City2>();

Variable names should begin with a lowercase letter: city vs City
The name of a list should reflect what is in the list. cities would be a list of cities, city is singular and does not represent a list.


Are you sure that method is ever used or called? Add a print statement to show that it is executed.

AH hell it is not being called! And nothing is coming out of it because it isnt getting called... Not sure of what to do now.
Tried with a print statement but all i get is five zeros on a line one after eachother.


Print looks like this:

0
0
0
0
0
0
0
23642 Höllviken
35243 Växjö
51000 Jönköping
72211 Västerås
75242 Uppsala
90325 Umeå
96133 Boden

Is doing something... it is doing "1-1"... basically.
But it has override too... i don't get it?!

all i get is five zeros

What print statement creates those zeros? Please post the code.

This is from the main :

	while ((currLine = r.readLine()) != null) {
				if (currLine.trim().length() > 0) {
					String[] split = currLine.split(";"); // We tell it where it should split.
					Z = (Integer.parseInt(split[0])); // We one value of the integers.
					C = (split[1]); // Same with the characters.
					City2 d = new City2(Z, C); // We put them in the other class.
					cities.add(d); // We also add them in the array list for "City2".
 
 
					System.out.println(d.compareTo(d)); //This part right here prints out Zeros.. But i cannot put anything else in the "d" spot of compareTo. 
 
 
 
				}
			}

  d.compareTo(d)

Look at what the compareTo method does. It subtracts two values and returns the results. Where do the two values come from?
They both come from the object referenced by d. A value minus itself will give 0


I was suggesting that the print statement be placed inside of the compareTo method to show if it was being called by the sort method.

Well it is not being called. Just checked with a print inside the method.

it is not being called.

Ok, why not? Where in you code is it supposed to be called?

Originally Posted by Norm

Ok, why not? Where in you code is it supposed to be called?

No idea tbh. I never thought about it and was caught up with just trying to get the right values out.
But now i want the compareTo to work. Just don't know of how to make that happen.

how to make that happen

Use a sort method that takes a list/collection of objects that implement the Comparable interface. Read the API doc for the different sort methods.

http://docs.oracle.com/javase/8/docs/api/index.html