For example, a Java program obtains file I/O (input/output) services by creating objects from various file-related classes in Java’s class library and calling their methods.

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.

Java Supplier interface tutorial. As you can see, the code for the class that implements Java’s Supplier interface is fairly simple. The only requirements are the class declaration and the ...