What’s often confusing to Java beginners is that classes also have interfaces. As I explained in Java 101: Classes and objects in Java, the interface is the part of the class that is accessible ...

Java lets you declare interfaces inside of classes. Once declared, an interface is automatically a static member of the class. There is no need to declare the interface with the static keyword.

BooleanSupplier, LongSupplier, DoubleSupplier LongUnaryOperator, DoubleUnaryOperator, IntUnaryOperator As you can see, the various Java functional interfaces simply provide a somewhat different spin ...