java.lang.ref: A collection of reference-related language classes, such as SoftReference and ReferenceQueue, organized in the ref sub-subpackage of the java package’s lang subpackage ...

The Java Function interface is quite simple. It takes a single Java object as an argument, and returns a single Java object when the method concludes. Any method you can conjure up takes an object and ...

See the Java 101 Java interfaces tutorial for a more in-depth introduction to using interfaces in your Java programs, including where and where not to use default, static, and private methods.