The JavaTM Tutorial
Previous Page Lesson Contents Next Page Start of Tutorial > Start of Trail > Start of Lesson Search
Feedback Form

Trail: Learning the Java Language
Lesson: Interfaces and Packages

Using an Interface as a Type

When you define a new interface, you are defining a new reference data type. You can use interface names anywhere you can use any other data type name. Recall that the data type for the first argument to the watchStock method in the StockMonitor class is StockWatcher:
public class StockMonitor {
    public void watchStock(StockWatcher watcher,
                           String tickerSymbol, double delta) {
    ...
    }
}
Only an instance of a class that implements the interface can be assigned to a reference variable whose type is an interface name. So only instances of a class that implements the StockWatcher interface can register to be notified of stock value changes. StockWatcher objects are guaranteed to have a valueChanged method.

Previous Page Lesson Contents Next Page Start of Tutorial > Start of Trail > Start of Lesson Search
Feedback Form

Copyright 1995-2004 Sun Microsystems, Inc. All rights reserved.