Java Reference
In-Depth Information
constant havingthesame typeandvalue, thecompiler will reportanerrorwheniten-
counters
X
in
Collision
'ssecond
foo()
methodbecauseitdoesnotknowwhich
X
is being inherited.
Speakingof
foo()
,thecompilerreportsanerrorwhenitencounters
Collision
's
second
foo()
declarationbecause
foo()
hasalreadybeendeclared.Youcannotover-
load a method by changing only its return type.
Thecompilerwillprobablyreportadditionalerrors.Forexample,theJava7compiler
has this to say when told to compile
Listing 2-45
:
Collision.java:16: error: foo() is already defined in Col-
lision
public int foo() { return X; }
^
Collision.java:11: error: Collision is not abstract and
does not override abstract
method
foo() in B
class Collision implements A, B
^
Collision.java:14: error: foo() in Collision cannot imple-
ment foo() in B
public void foo();
^
return type void is not compatible with int
Collision.java:16: error: reference to X is ambiguous, both
variable X in A and
variable X
in B match
public int foo() { return X; }
^
4 errors
Extending Interfaces
Justasasubclasscanextendasuperclassviareservedword
extends
,youcanusethis
reservedwordtohavea
subinterface
extenda
superinterface
.This,too,isknownas
in-
terface inheritance
.
