The Java API is full of terrific interface definitions. One commonly used interface is java.lang.Runnable, which can be implemented to create a thread. To write an interface, you can look at the many good examples in the Java API. When writing your own, you just use the keyword interface instead of class , and then don't include the method implementations . Like this: public interface MyInterface { public void someMethod(long someParam); } As you can see, you just use the interface keyword in place of class . And then you substitute a semi- colon for the curly braces holding the method implementation. That's all you have to do in a nutshell . In the following sections, we'll see the many twisting, cavernous corridors that lurk beneath the deceptively simple interface. After you have an interface, you implement it. That means you declare a class that implements the interface, and then write the implementation for each method in the interface. And the method signatures must match exactly. Like this: public MyClass implements MyInterface { //since I said "implements MyInterface", //I must include this method, or //this class won't compile public void someMethod(long someParam) { //this is my implementation. } } You can add methods and other stuff to your implementing class if you want to. |