Interfaces and Polymorphism - Java Concepts - page 595

by adding a number of String objects. (The String class implements
the Comparable interface.)

΢ Exercise P9.10. Modify the Coin class to have it implement the
Comparable interface.

΢΢΢ Exercise P9.11. The System.out.printf method has predefined
formats for printing integers, floating-point numbers, and other data
types. But it is also extensible. If you use the S format, you can print any
class that implements the Formattable interface. That interface has a
single method:

void formatTo(Formatter formatter, int
flags, int width, int precision)

In this exercise, you should make the BankAccount class implement
the Formattable interface. Ignore the flags and precision and simply
format the bank balance, using the given width. In order to achieve this
task, you need to get an Appendable reference like this:

Appendable a = formatter.out();

Appendable is another interface with a method

void append(CharSequence sequence)

CharSequence is yet another interface that is implemented by (among
others) the String class. Construct a string by first converting the bank
balance into a string and then padding it with spaces so that it has the
desired width. Pass that string to the append method.

433
434

΢΢΢ Exercise P9.12. Enhance the formatTo method of Exercise P9.11 by
taking into account the precision.

΢΢GExercise P9.13. Write a method randomShape that randomly
generates objects implementing the Shape interface: some mixture of
rectangles, ellipses, and lines, with random positions. Call it 10 times and
draw all of them.