第5章继承、接口与泛型资料.ppt

* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * class TalkingClock { public TalkingClock(int interval, boolean beep) { this.interval = interval; this.beep = beep; } public void start() { ActionListener listener = new TimePrinter(); Timer t = new Timer(interval, listener); t.start(); } private int interval; private boolean beep; private class TimePrinter implements ActionListener { public void actionPerformed(ActionEvent event) { Date now = new Date(); System.out.println(At the tone, the time is + now); if (beep) Toolkit.getDefaultToolkit().beep(); } } } * 5.15 内部类inner class The TimePrinter class has no instance field or variable named beep. Instead, beep refers to the field of the TalkingClock object that created this TimePrinter. This is quite innovative. Use of an Inner Class to Access Object State * 5.15 内部类inner class Traditionally, a method could refer to the data fields of the object invoking the method. An inner class method gets to access both its own data fields and those of the outer object creating it. How to do this? Use of an Inner Class to Access Object State * 5.15 内部类inner class an object of an inner class always gets an implicit reference to the object that created it. Use of an Inner Class to Access Object State * 5.15 内部类inner class This reference is invisible in the definition of the inner class. However, to illuminate the concept, let us call the reference to the outer object outer. Then, the actionPerformed method is equivalent to the following: public void actionPerformed(ActionEvent event) { Date now = new Date(); System.out.println(At the tone, the time is + now); if (outer.beep) Toolkit.getDefaultToolkit().beep(); } Use of an Inner Class to Access Object State * 5.15 内部