Java Reference
In-Depth Information
Methods that are not specified as
static
can access any of the variables in the class directly.
Recursive methods are methods that call themselves.
Access to members of a class is determined by the access attributes that are specified for each
of them. These can be
public
,
private
,
protected
, package
private
, or nothing at all.
Classes can be grouped into a package. If a class in a package is to be accessible from outside
the package the class must be declared using the keyword
public.
To designate that a class is a member of a package you use a
package
statement at the
beginning of the file containing the class definition.
To add classes from a package to a file you use an
import
statement immediately following
any package statement in the file.
A native method is a method implemented in a language other than Java. Java programs
containing native methods cannot be applets and are no longer portable.
A field does not get ploughed by turning it over in your mind.
Exercises
1.
Define a class for rectangle objects defined by two points, the top-left and bottom-right
corners of the rectangle. Include a constructor to copy a rectangle, a method to return a
rectangle object, that encloses the current object and the rectangle passed as an argument, and
a method to display the defining points of a rectangle. Test the class by creating four
rectangles, and combining these cumulatively, to end up with a rectangle enclosing them all.
Output the defining points of all the rectangles you create.
2.
Define a class,
mcmLength
, to represent a length measured in meters, centimeters, and
millimeters, each stored as integers. Include methods to add and subtract objects, to multiply
and divide an object by an integer value, to calculate an area resulting from the product of two
objects, and to compare objects. Include constructors that accept: three arguments - meters,
centimeters, and millimeters; one integer argument in millimeters; one
double
argument in
centimeters and no arguments, which creates an object with the length set to zero. Check the
class by creating some objects and testing the class operations.
3.
Define a class,
tkgWeight
, to represent a weight in tons, kilograms, and grams, and include a
similar range of methods and constructors as the previous example. Demonstrate this class by
creating and combining some class objects.
4.
Put both the previous classes in a package called
Measures
. Import this package into a program
that will calculate and display the total weight of the following: 200 carpets - size: 4 meters by 2
meters 9 centimeters, that weigh 1.25 kilograms per square meter; and 60 carpets - size: 3 meters
57 centimeters by 5 meters, that weigh 1.05 kilograms per square meter.
