In this case, String::toUpperCase is an instance method reference. The instance method reference refers to the toUpperCase() method that is called on instances of String.

In Java, we don’t need to write “THEN.” Instead, we use an open curly bracket to say that everything that follows is part of that “code block” and should run under the conditions we specify.

I’ve used assert to check the postcondition of x being sorted before sort() returns to its caller. The example in Listing 4 demonstrates an important characteristic of assertions, which is that ...