Java Reference
In-Depth Information
12
.
An action listener must have a method called
actionPerformed
.
13
.
A
class
is a collection of data members and methods associated with those
data members.
14
.
OOD starts with a problem statement and tries to identify the classes
required by identifying the nouns appearing in the problem statement.
15
.
Methods of a class are identified with the help of verbs appearing in the
problem statement.
16
.
To wrap values of primitive data types into objects corresponding to each
primitive type, Java provides a
class
, called a wrapper class. For example,
to wrap an
int
value into an object, the corresponding wrapper
class
is
Integer
. Similarly, to wrap a
double
value into an object, the corre-
sponding wrapper
class
is
Double
.
17
.
Java 5.0 simplifies the wrapping and unwrapping of primitive type values,
called the autoboxing and auto-unboxing of primitive data types.
18
.
Integer
objects are immutable. (In fact, wrapper classes' objects are
immutable.)
19
.
To compare the values of two
Integer
objects, you can use the method
compareTo
. If you want to compare the values of two
Integer
objects
only for equality, then you can use the method
equals
.
EXERCISES
1.
Mark the following statements as true or false.
a.
Every window has a width and height.
b.
In Java,
JFrame
is a class.
c.
To display the window, you need not invoke a method such as
setVisible
.
d.
In Java, the reserved word
extends
allows you to create a new class
from an existing one.
e.
The window you see displayed on your screen is a class.
f.
Labels are used to display the output of a program.
g.
Every GUI component you need has to be created and added to a
container.
h.
In Java,
implements
is a keyword.
i.
Clicking a button is an example of an action event.
j.
In a problem statement, every verb is a possible class.
k.
In a problem statement, every noun is a possible method.
l.
To use an object, you must know how it is implemented.
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