The Java Tutorials have been written for JDK 8. Examples and practices described in this page don't take advantage of improvements introduced in later releases and might use technology no longer available.
See Dev.java for updated tutorials taking advantage of the latest releases.
See Java Language Changes for a summary of updated language features in Java SE 9 and subsequent releases.
See JDK Release Notes for information about new features, enhancements, and removed or deprecated options for all JDK releases.
An interface declaration can contain method signatures, default methods, static methods and constant definitions. The only methods that have implementations are default and static methods.
A class that implements an interface must implement all the methods declared in the interface.
An interface name can be used anywhere a type can be used.