The argument to the method should be java.util.function.Consumer. This is an interface that requires the accept() method to be defined, and this method is void. The lambda expression or a class that implements this interface will consume the argument of the accept() method and does not produce anything.
There are several other interfaces defined in that package, each serving as a functional interface used to describe some method arguments that can be given as lambda expressions in the actual parameters.
For example, the opposite of Consumer is Supplier. This interface has a method named get() that does not need any argument, but that gives some Object as a return value.
If there is an argument and also a returned value, ...
