After we’ve named our method, we use brackets in order to add any arguments. An argument is a variable that we wish to pass from one method to another. Variables are values represented by words.

In Java, we can implement the functional interface with a lambda expression and pass it to a method, then execute the function after an operation is finished. Here’s how that looks in code: ...

assert BooleanExpr : expr; Here, expr is any expression (including a method invocation) that can return a value—you cannot invoke a method with a void return type.

In the Method Handles API, introduced in Java 7, this role is fulfilled by the java.lang.invoke.MethodType class, which uses immutable instances to represent signatures.