Trying to write a circle program

I've been trying to teach myself some Java language as part of a computer literacy regimen, and for the life of me I cannot get this circle identifier program debugged or working. The goal is that the user inputs what type of data they have about a circle, and working out the area from that.

Code:

`import java.util.Scanner;`

public class IdentifyCircle

{

public static void main(String[] args)

{

final double pi = 3.14159;

double areafromradius = pi * radiusdata * radiusdata;

double areafromdiameter = pi * diameterdata;

double areafromcircumference = circumferencedata / pi * 2;

Scanner in = new Scanner(System.in);

System.out.println("Radius, diameter, or circumference?");

String type = in.nextLine();

if (type == "Radius");

{

System.out.println("What is your radius?");

double radiusdata = in.nextLine();

System.out.println("The area of a circle with radius " + radiusdata + " is " + areafromradius);

}

if (type == "Diameter");

{

System.out.println("What is your diameter?");

double diameterdata = in.nextLine();

System.out.println("The area of a circle with diameter " + diameterdata + " is " + areafromdiameter);

}

if (type == "Circumference");

{

System.out.println("What is your circumference?");

double circumferencedata = in.nextLine();

System.out.println("The area of a circle with circumference " + circumferencedata + " is " + areafromcircumference);

}

}

}

I also cannot work out a formula to find area from circumference, and thus am just using a dummy working one until I can. There is some conflict between using the "double" for my data and "String" for my type... I cannot get my head around it. Furthermore, should I temporarily and superficially resolve these, the whole program runs irrespective of what the user inputs... This code project has proven the most difficult, although it is my most ambitious to date. I know, right, this is... complicated stuff... But regardless, one need start somewhere. Any suggestions, adjustments, or corrections would be much appreciated!