Question

How do I create two or more classes that interact with each other?
For example, a method in the first class will be static, producing a Fibonacci number for instance, and another method in the second class will do something with the Fibonacci number which has been created by the method in first class, and how do I extend my classes?

Answer 1

Since it seems that you are beginning to code in java, I’d say that this oracle article about Modifiers are a good start to understand how a Class can interact with another.

So to answer your questions:

So how do i make 2 or more classes that interact with each other ?

There are several ways for one class to interact with another one. Please be aware that I’ve selected the ones I’ve found more useful for your particular example. The most common of them are

• Instance of Class Bar call a method from another instance of a Class Foo like the example below:

  Foo foo = new Foo()
  Bar bar = new Bar();
  
  bar.setSomeFieldValue(foo.getSomeOtherFieldValue());
  

• Class Foo extends Class Bar and call a construct defined on it’s super class: This tries to answer your question on: How you extend a Class

  Class Foo extends Bar
  {
      public Foo()
      {
          super(); //Calling the Bar Class construct
      }
  }
  

• Class Foo expect an instance of Class Bar as an argument of a method:

  import dir.barpackage.Bar;
  
  Class Foo
  {
      private int x;
  
      public Foo()
      {
          //Construct an Instance of the Foo object
      }
  
      public void doSomethingWithBar(Bar bar)
      {
          Foo.x = bar.getSomeBarPropertyValue();
      }
  }
  

Going further on your question:

For example, a method in the first class will be static, producing a Fibonacci number for instance, and another method in the second class will do something with the Fibonacci number which has been created by the method in first class

The following example is one way of doing this:

FirstClass.java

Class FirstClass
{
    private static int fibonnacciNumber; // This field is private to this class and thus can be only accessed by this class

    public static int getFibonnaciNumber() // A public method can be accessed any place other than your class
    {
        return FirstClass.fibonnacciNumber;
    }
}

SecondClass.java

Class SecondClass
{
    public void doSomethingWithFibonnacciNumber(int fibonnacciNumber)
    {
        //Will do something with your fibonnacci number;
    }
}

Example of usage

SecondClass second = new SecondClass();
second.doSomethingWithFibonnacciNumber(FirstClass.getFibonnacciNumber());

I hope it helped. Cheers.