New to Java

Hi Guys, Sorry to bother you all, but I am hoping for some assistance in fixing this code. The project is from my "Programming in Java" course, and its to work with "Try and Switch" statements. I believe there are errors in the logic that force NumberFormatExceptions (on purpose) but I am not sure. Also I cannot seem to get the cancel button to work correctly. Its already throwing a "null" value, as verified by System.out.print statements, but the Cancel button is throwing aNumberFormatException. I am so confused right now. Here is the code ...

import java.io.*;
import javax.swing.JOptionPane;

public class MyType
{//Class Open

	public static void main(String[] args)//throws IOException
	{//Main Open
	
		//Delcare variables
		String strChoice, strTryString, strTryInt, strTryDouble, strTryLong, strTryByte, strTryBoolean;
		int choice, tryInt;
		double tryDouble;
		
		long tryLong; //extra credit
		byte tryByte; //extra credit
		boolean tryBoolean; //extra credit
		
		boolean done = false;
								
		//loop while not done until user clicks the cancel button
		while(!done)
		{//While Open
		
			try //inside a try statement, enter code to display and input box with 3 choices
			{//Try Open
			
				strChoice =(JOptionPane.showInputDialog(null, "What is My Type?" + "\n\n1) String\n2) Integer\n3) Double\n4) Long\n5) Byte\n6) Boolean\n7) Quit the program\n\n"));
			
				choice = Integer.parseInt(strChoice);
				
				// Error Messages inform me of Strings not initialised 
				strChoice = null; 
				strTryInt = null; 
				strTryDouble = null;
				strTryLong = null;
				strTryByte = null;
				strTryBoolean = null;
								
				if (choice == 0) System.exit(0);
				
				System.out.println(strChoice);
				System.out.println(strTryDouble);
				System.out.println(strTryInt);
				System.out.println(strTryLong);
				System.out.println(strTryBoolean);
				
			switch(choice)
			{//Switch Open
				case 1://If Users enter a 1, display "correct" message 
					JOptionPane.showMessageDialog(null, "Very Nice! That is Correct, Because any input can be saved as a String!");
					break;
					
				case 2://If User enters a 2, parse the value into tryInt, Inform users they are correct
					tryInt = Integer.parseInt(strTryInt);
								System.out.println(choice);
								JOptionPane.showMessageDialog(null, "You are Correct!");
					break;
					
				case 3://If User enters a 3, parse value into tryDouble, Inform users they are correct
					
					tryDouble = Double.parseDouble(strTryDouble +.1);
								System.out.print(choice); 
								JOptionPane.showMessageDialog(null,  "That is Correct!");
					break;
				case 4://extra credit Long
					tryLong = Long.parseLong(strTryLong);
					JOptionPane.showMessageDialog(null, "That is Correct!");
					break;
				
				case 5: //extra credit Byte 
					tryByte = Byte.parseByte(strTryByte);
					JOptionPane.showMessageDialog(null, "That is Correct!");
					break;
					
				case 6: //extra credit Boolean 
					tryBoolean = Boolean.valueOf(strTryBoolean);
					JOptionPane.showMessageDialog(null, "That is Correct!");
					break;
					
				case 7://set done equal to true, code closing message
					done = true;
								JOptionPane.showMessageDialog(null, "Thanks for trying MyType");
					break;
									
				default: throw new NumberFormatException(); 
				
								
			}//Switch Close
				//if(strChoice == null) System.exit(0);
				
			}//Try Close
			
			catch(NumberFormatException e)
			
			{//Catch Open
				JOptionPane.showMessageDialog(null,"OOOPS! try again", "Not a String Error", JOptionPane.INFORMATION_MESSAGE);
				
			}//Catch Close
			
		}//While Close

		
		//
		
	}//Main Close
	
				
		
	
	
	
}//Class Close

Any assistance would be greatly appreciated.