Working with Objects - Java 6 - page 72

A character can be used as an int because each character has a
corresponding numeric code that represents its position in the
character set. If the variable i has the value 65 , the cast (char)i
produces the character value A . The numeric code associated with
a capital A is 65, according to the ASCII character set, and Java
adopted this as part of its character support.

NOTE

You must use an explicit cast to convert a value in a large type to a smaller type, or else
converting that value might result in a loss of precision. Explicit casts take the following
form:

( typename ) value

In the preceding example, typename is the name of the data type to which you're con-
verting, such as short , int , or float . value is an expression that results in the value of
the source type. For example, in the following statement, the value of x is divided by the
value of y , and the result is cast into an int in the following expression:

int result = (int)(x / y);

Note that because the precedence of casting is higher than that of arithmetic, you have to
use parentheses here; otherwise, the value of x would be cast into an int first and then
divided by y , which could easily produce a different result.

Casting Objects
Instances of classes also can be cast into instances of other classes, with one restriction:
The source and destination classes must be related by inheritance; one class must be a
subclass of the other.

Some objects might not need to be cast explicitly. In particular, because a subclass con-
tains all the same information as its superclass, you can use an instance of a subclass
anywhere a superclass is expected.

For example, consider a method that takes two arguments, one of type Object and
another of type Component . You can pass an instance of any class for the Object argu-
ment because all Java classes are subclasses of Object . For the Component argument, you
can pass in its subclasses, such as Button , Container , and Label .

This is true anywhere in a program, not just inside method calls. If you had a variable
defined as class Component , you could assign objects of that class or any of its subclasses
to that variable without casting.