How to call a method from another class?

[jboy]

Hi,

I just need to know what options I have to call a method from another class? because my program consists of multiple classes and the only way that I think of calling a method is to create an instance of a class and then call the class method using the instance.mehod. Are there any other ways that I can call methods from a different class?

Thank you.

[mtyoung]

if the method is static, you can call method by Class.method() like Integer.toString(123)

[jboy]

Oh, really. Thanks heaps for pointing this out for me, I always thought there must be a way we could call a method from other classes and now I have a better control over using the methods from other classes because I don't need to create an object of a class anymore. But what is the purpose of static method? Is there any risks involved? Also, is there any other way that I am unaware for calling methods?

Thanks again,

[r035198x]

You should be reading Sun's tutorial for those things.
Generally you should be avoiding static methods in OOP.

[jboy]

I have a small problem with my following code where I am trying to access the static method in the root class. I don't know how to relate date.add(..) in the addDate method in my other class to the root class.

This is my root class:

import java.text.*;
import java.util.*;

public class Car
{  private static GregorianCalendar date = new GregorianCalendar();
    public static void main(String[] args)
   { new Car();
      date.setLenient(false);}		

      public static void setStart()
      {	date.set(GregorianCalendar.YEAR, 2008);
    	date.set(GregorianCalendar.MONTH, 1);
    	date.set(GregorianCalendar.DATE, 1);   	}

}

This is a piece of my other class:

	private String getDate()
	{   System.out.print("\t\t\tDay: ");
	    day = In.nextInt();
	    System.out.print("\t\t\tMonth: ");
	    month = In.nextInt();
	    System.out.print("\t\t\tYear: ");
	    year = In.nextInt();
	    return addDate(day, month, year);	}

	private String addDate(int day, int month, int year)
	{	date.add(date.get(5), day);
		date.add(date.get(2)+1, month);
		date.add(date.get(1), year);
		return sdf.format(date);	}

[mtyoung]

how do setStart related to addDate?

[jboy]

That is what I need to do that is to relate addDate to setStart. The program reads the integar numbers entered by the user and add them to the setStart date.

[mtyoung]

add input parameters to setStart method, pass year, month and day inputs

[quad64bit]

also, if all your methods are private, you cannot call them from another class if that class is in a separate file. I suggest you don't use static at this point until you are more comfortable with the language.

Why not use a driver style structure? Class Driver contains an instance of class A and Class B, and you can give a reference of A to B or vice versa, or not at all. For example:

public class Driver {
    public static void main(String[] args) {
        new Driver();
    }

    public Driver(){
        B b = new B();
        A a = new A(b);
        System.out.println(a.getGreeting());
        System.out.println(b.getName());
    }
}

public class A{
    private B b;
    
    public A(B b){
        this.b = b;
    }

    public String getGreeting(){
        return "Hello " + b.getName();
    }
}

public class B{
    public String getName(){
        return "Ralph";
    }
}

In this example, the driver is the main portion of the program. It controls everything. I created an instance of class B and then an instance of class A. Class A takes a reference to class B in it's constructor. In A, you can see that it calls a method that belongs to B. You can also see that I call a method in B directly from the Driver. You can rearrange this setup any way you please.

When I code, I tend to have many independent objects (separate class files) that are all linked together with a Driver of sorts. If two different classes need to talk to eachother, they can either do it through the Driver with accessor methods, or directly by storing a reference to each other. Here is another example using accessor methods in the Driver:

public class Driver {
    public static void main(String[] args) {
        new Driver();
    }
    
    private B b;
    private A a;
    
    public Driver(){
        b = new B();
        a = new A(this);
    }
    
    public void tellBToPrint(){
        b.printSauce();
    }
}

public class A{
    public A(Driver driver){
        printTaco();
        driver.tellBToPrint();
    }
    
    public void printTaco(){
        System.out.println("Crunch taco");
    }
}

public class B{
    public void printSauce(){
        System.out.println("Spicy");
    }
}