Functional interfaces

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, ...

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