Accessing methods in another non-static class

Question

0.00/5 (No votes)

See more:

I have 3 classes handling data members:
Save
Memory
Number

each with a Ctor, setters, getters, and various other things they require.
And data members.

I have a class:
Calculator

which has to operate on the variables stored in the aforementioned classes.

I don't want to create objects from those classes in Calculator, since I already created such objects from main()!!!!

So how can I access them?

I tried changing the functions to static,
for instance:

Java

public static double Add() {
return Number.getNumber() + Save.getSave();
}

(in Calculator, which is an abstract class...)

That would be how I'd access static methods in abstract classes, but but it wouldn't let me, since they handle data members - I couldn't even change the methods to static without getting an error...

If I were to create a new object from, say, class Number, it would have its own data members, whereas I want to access the data members in the object created by main()!!!

Can I retrieve a reference and use it somehow, or something like that?

Thanks for helping.

Posted 28-Dec-12 3:05am

teledoar

Updated 28-Dec-12 3:28am

v4

Add a Solution

Comments

TorstenH. 30-Dec-12 2:58am

You really need to read about OOP and the usage of variables.
This looks really odd, that's not the way to use any programming language.

PLease follow the link I posted about the abstract classes,there is a complete Java Tutorial behind it, really well written.

Also, please get a decent JAVA book that you can place beside your keyboard to have a look at topics while coding. Books are still a perfect source for learning.

EDIT: I have added another solution, please check it out. it explains the basic rules of abstraction

3 solutions

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

TorstenH. · Answer 1 · 2012-12-28T04:20:00

Solution 1

Please do not use static. You should create instances or use the given instances in Calculator by using setters there:

Java

public class MyCalculator extends Calculator{ // extending the abstract class

  public MyCalculator(){
    this.ignition();
  }

  private void ignition(){
    // this is where the fun starts

    setIntegerValue(2); // example for an inherited setter from Calculator
  }



  public static void main(String[] args]{
    MyCalculator oCalc = new MyCalculator(); // break out of static context
  }
}

Posted 28-Dec-12 4:20am

TorstenH.

Comments

teledoar 28-Dec-12 11:32am

Err... calculator doesn't have any data members, so it doesn't have a setter.
I'm trying to use the getter function from classes Save and Number in class Calculator.

TorstenH. 28-Dec-12 14:01pm

whatever. it's an example.
I do not have your classes and therefor do not know what's inside.

You can see in that example how to extend a given abstract class and how to use it's methods in a non-static way.
Please try to develop from that scratch your own code.

teledoar 28-Dec-12 15:53pm

Point is, my classes don't inherit from Calculator, they are entirely unrelated to it or each other, they are there simply to hold data and code, but they need to use variables and functions from one another. That is the problem, I already know how to inherit things.

By now, I solved it already by making everything - variables included - static. Now I can access them all from everywhere;

I'd still like to know how to access methods (and/or) variables in unrelated classes that are not abstract/static. (public ones, naturally). 'Cause so far I've been stymied whenever I tried.

TorstenH. 29-Dec-12 5:13am

Your design is leaking just a little bit (like e.g. a waterfall).

You should read about the concept of abstract classes ( Abstract classes @ the Java Tutorial ).
You need to extend the abstract classes - you can also do so beside of your existing code and then use the extending classes (YES, by variable and instance, cause that's how programming works!)

Using static just to be able to access variables is bad, really bad.

teledoar 2-Jan-13 13:47pm

I asked my teacher and he explained to me what you've meant by "leaking". Anyway, he says what I did in the first place ought to have worked, and didn't know why I got red all over it without me showing it to him.

Unfortunately, I already turned it all to static, and change the reference to all of it all over my classes to a static way, so now I have to change it all back before I can try and see why it didn't work.

If only I had the time... <sigh>

Thanks, anyway.

teledoar 2-Jan-13 13:50pm

I think I should have written:
public static double Add() {
return Calculator.Number.getNumber() + Calculator.Save.getSave();
}

TorstenH. 2-Jan-13 15:44pm

check out Solution 3, that is what you need.

Yes, it might have worked and if you have a chance to change access to the methods in the abstract class to static, you can also do that too.
Normally you can not alter a method of a abstract class in an extension to be static - that is not allowed.
Often one has to deal with libraries, where a class is given and needs to be extended. One can not change the given classes / objects, but has to cover own functionality.

As an example: I do so often with GUI components. I add some functionally to them by extending them.
Like highlighting when mandatory fields that are empty or validation routines on text fields that the user enters e.g. telephone number or zip code.
Also are tables always custom - one just uses a base class / an interface that get's extended / filled to what is needed.

Please count it as a lesson learned and remember next time.

John d. Bartels · Answer 2 · 2012-12-29T13:09:00

C#

public class ExampleClass
{
    public string ECName { get; set; }
    public int ECIndex { get; set; }
    public string ECDescription { get; set; }

    public bool checkOtherClassValue(OtherExampleClass oecTemp)
    {
        if (oecTemp.someValue == &quot;someValue&quot;)
        {
            return true;
        }
        else
        {
            return false;
        }
    }
}

public class OtherExampleClass
{
    public string someValue { get; set; }
    public int oecIndex { get; set; }
}

Then, in main, create both of your objects:

C#

//Create an object of one class
OtherExampleClass oecTemp = new OtherExampleClass();
//set some values...
oecTemp.someValue = "someValue";

//create an object of another class
ExampleClass ec = new ExampleClass();
//pass the first object as a param for the method in the second class

bool result = ec.checkOtherClassValue(oecTemp);

You could also create a getter method in main that returns the object based upon a requested index or name etc.

TorstenH. · Answer 3 · 2012-12-29T21:22:00

OK, let's try again.

I created a class Application.
This is my application - surprising, I know.
Please also regard the break out of the static context.

There is an abstract class MyAbstractClass that has some method.
And there is a class MyClass that extends MyAbstractClass.

There is also a function parseIntFromString(int), that is part of the abstract class. I'm changing it in MyClass, so it returns the result I want (That works as long as a function is not set "final").

With the help of this extension MyClass I can access all the functions of the abstract class MyAbstractClass, as you can see in the function ignition()

Java

package com.cp;

public class Application {
	
	public Application(){
		this.ignition();
	}

	private void ignition() {
		MyClass oMyClass = new MyClass();
		
		// using method from MyClass
		System.out.println("The result is " + oMyClass.tellIfPositive(3) );
		
		// using method from abstract class via MyClass
		System.out.println("The result is " + oMyClass.tellIfTrue(0));
		
		// using altered method - abstract would return 0
		System.out.println("The result is " + oMyClass.parseIntFromString("2"));
	}

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		new Application(); // break out of static context
	}
	
//	#############################################################
//	Extending the abstract class
//	it inherits the functions of the abstract class and can have additional functions.
	public class MyClass extends MyAbstractClass{
		
		public MyClass(){ /* doAny(); */}
		
		public boolean tellIfPositive(int iValue){
			if(0 <= iValue){ return true; }
			return false;
		}
		
		// function is altered to return result we need
		@Override
		public int parseIntFromString(String strValue){
			return Integer.parseInt(strValue);
		}
	}
	
//	##############################################################	
	// abstract class with a method we want to use.
	public abstract class MyAbstractClass {

		// just a simple function, nothing serious
		public boolean tellIfTrue(int iValue){
			if(1 == iValue){ return true; }
			return false;
		}
		
		// function that is going to be altered in MyClass
		public int parseIntFromString(String strValue){
			return 0;
		}
	}
	
//	################################################################

}

Accessing methods in another non-static class

3 solutions

Solution 1

Solution 2

Solution 3

Add your solution here

Preview 0

Existing Members

...or Join us