Creating Windows - Beginning Java 2 SDK - page 655

You can also test and compare Rectangle objects in various ways with the following methods:

Method Description

boolean isEmpty() Returns true if the width and height members of the

current Rectangle object are zero, and false otherwise.

boolean equals(
Object rect)

Returns true if the Rectangle object passed as an argument
is equal to the current Rectangle object, and returns false
otherwise.

The two rectangles will be equal if they are at the same
position and have the same width and height. If the argument
is not a Rectangle object, false is returned.

boolean intersects(
Rectangle rect)

Returns true if the current Rectangle object intersects the
Rectangle object passed as an argument, and false
otherwise.

boolean contains(
Point p)

Returns true if the current Rectangle object encloses the
Point argument p , and false otherwise.

boolean contains(
int x, int y)

Returns true if the current Rectangle object encloses the
point ( x , y ), and false otherwise.

All of these will be useful when dealing with the contents of a Java window. You will then be dealing
with points and rectangles describing the contents drawn in the window. For example, you might want
to enable the user of your program to select some geometric shape from among those displayed on the
screen, in order to work with it. You could use the contains() method to check whether the point
corresponding to the current cursor position is within any of the Rectangle objects that enclose each
of the circles, lines, or whatever is displayed in the window. Then you can decide which of the objects
displayed on the screen the user wants to choose.

There are other classes defining rectangles that we shall meet when we start drawing in a window.

Visual Characteristics of a Component

Two things determine the visual appearance of a component: the representation of the component
created by the Java code in the component class that is executed when the component is displayed, and
whatever you draw on the component. You can draw on a Component object by implementing its
paint() method. We used this method in Chapter 1 to output the text for our applet. The paint()
method is called automatically when the component needs to be drawn.

The need to draw a component can arise quite often for a variety of reasons - for example, your
program may request that the area that the component occupies should be redrawn, or the user may
resize the window containing the component. Your implementation of this method must include code to
generate whatever you want drawn within the Component object. Note that the component itself - the
JButton or JFrame or whatever, will be drawn for you. You only need to override the paint()
method for anything additional that you want to draw on it. We will be overriding the paint()
method in Chapter 17 to draw in a window, so we will leave further discussion of it until then.