No instance(s) of type variable(s) t exist so that void conforms to t

When you encounter the error message “no instance(s) of type variable(s) t exist so that void conforms to t,” it means that there is a type mismatch between a method that returns void and a generic type argument used when invoking that method. In simple terms, you are trying to use a type that does not match the expected return type of the method.

Let’s consider an example to understand this error better. Suppose we have a generic method called printValue that prints the value of a given generic variable. The method has the following signature:

      
         public <T> void printValue(T value) {
            System.out.println(value.toString());
         }
      
   

Now, let’s assume we have a class with a main method where we are trying to invoke the printValue method with an integer argument:

      
         public class Main {
            public static void main(String[] args) {
               Main main = new Main();
               main.printValue(10);
            }
         }
      
   

In this case, you will encounter the “no instance(s) of type variable(s) t exist so that void conforms to t” error. This is because the printValue method is expecting a generic type argument, but we have provided an integer argument which corresponds to a specific type (int) and not a generic type. Hence, the type mismatch occurs.

To resolve this error, you need to provide a generic type argument when invoking the printValue method. In this example, you can change the main method as follows:

      
         public static void main(String[] args) {
            Main main = new Main();
            main.<Integer>printValue(10);
         }
      
   

By specifying the generic type argument <Integer>, you are telling the compiler that the printValue method should expect an integer argument. This resolves the type mismatch error, and the code will compile and execute successfully.