Java Reference
In-Depth Information
if (anObject instanceof BankAccount)
{
BankAccount anAccount = (BankAccount) anObject;
. . .
}
The instanceof operator tests whether an object belongs to a particular type.
S YNTAX 10.4 The instanceof Operator
object instanceof TypeName
Example:
if (anObject instanceof BankAccount)
{
BankAccount anAccount = (BankAccount) anObject;
. . .
}
Purpose:
To return true if the object is an instance of TypeName (or one of its subtypes),
and false otherwise
S ELF C HECK
10. Why did the second parameter of the transfer method have to be of
type BankAccount and not, for example, SavingsAccount ?
11. Why can't we change the second parameter of the transfer method to
the type Object ?
454
455
10.6 Polymorphism
In Java, the type of a variable does not completely determine the type of the object to
which it refers. For example, a variable of type BankAccount can hold a reference
to an actual BankAccount object or a subclass object such as SavingsAccount .
You already encountered this phenomenon in Chapter 9 with variables whose type
was an interface. A variable whose type is Measurable holds a reference to an
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