Before JDK1.8 existing function interface
java.lang.Runnable
java.util.concurrent.Callable
java.security.PrivilegedAction
java.util.Comparator
java.io.FileFilter
java.nio.file.PathMatcher
java.lang.reflect.InvocationHandler
java.beans.PropertyChangeListener
java.awt.event.ActionListener
javax.swing.event.ChangeListener
JDK1.8 newly added function interface
# 这个包下面有好多函数式接口,就不一一列举了,感兴趣的可以去查查源码
java.util.function