Initialize object variable error

you can alter the code as:

 public class TapeDeck 
        {
           // code
        }

       public class TapeDeckTestDrive
        {
            public static void main(String [] args)
            {
                TapeDeck t = new TapeDeck(); 
                t.canRecord = true;
                t.playTape();

                if(t.canRecord == true) 
                {
                    t.recordTape();
                }
            }
        }

Instantiate your TapeDeck object

class TapeDeckTestDrive
{
    public static void main(String [] args)
    {
        TapeDeck t = new TapeDeck(); 
    ...

You need to create instance of TapeDeck and assign it to t reference. You can create instance using new keyword like

TapeDeck t; 
t = new TapeDeck();

or in one line

TapeDeck t = new TapeDeck();

Otherwise t stays uninitialized and you can't call any method on uninitialized variable.

BTW if(t.canRecord == true) is considered as code smell since it can lead to problems like if(variable=true) where we assign true to variable (=true) instead of comparing (==true). To avoid such problems simply use

if(t.canRecord)

or if you feel like having == and true increases readability so you don't want to remove them use yoda-condition

if(true == t.canRecord)

You can initialize using new and the name of your class, in your case TapeDesck();.

TapeDeck t = new TapeDeck();

If you don't do that you won't be able to use any of the methods inside of your class TapeDesck().

If you have a constructor, then you can initialize it with it. For example, if you have this constructor (it's just an example, don't focus on the name of the variables):

class TapeDesck
{
   private int number;
   private String prove;

   public TapeDesck(int number, String prove)
   {
       this.number = number;
       this.prove = prove;
   }
}

You can initialize it like this:

TapeDeck t = new TapeDeck(1,"This is a prove"); 

I expect it will be helpful for you!

You just declared the variable on the 1st line in your main():

TapeDeck t;  // Variable just declared not initialized.  

Solution:

TapeDeck t = new TapeDeck();  // Initialize it to use members.  

You seem to be from C++ background. This kind of initialization of objects are allowed in C++ but not in Java. You strictly have to use the new keyword to initialize an object.