Let's say I have the following two class/interface definitions:
public abstract class FooClass {
public abstract void doFoo();
}
and
public interface BarInterface {
public void doBar();
}
If I want to make an anonymous inner class that extends/implements both, do I need to do this:
public abstract class BothClass extends FooClass implements BarInterface {}
...
new BothClass() {
public void doFoo() {
System.out.println("Fooooooooo!!!!");
}
public void doBar() {
System.out.println("Baaaaaaaar!!!!");
}
}.doBar();
Or is there a short-cut that allows me to not define BothClass? Something like this, maybe:
new (FooClass implements BarInterface)() {
public void doFoo() {
System.out.println("Fooooooooo!!!!");
}
public void doBar() {
System.out.println("Baaaaaaaar!!!!");
}
}.doBar();
(This idea gives me several errors, none of which are helpful here)
解决方案
An anonymous class declaration is automatically derived from a class
instance creation expression by the Java compiler.
where a class instance creation expression is
ClassInstanceCreationExpression:
new TypeArgumentsopt TypeDeclSpecifier TypeArgumentsOrDiamondopt
( ArgumentListopt ) ClassBodyopt
Primary . new TypeArgumentsopt Identifier TypeArgumentsOrDiamondopt
( ArgumentListopt ) ClassBodyopt
TypeArgumentsOrDiamond:
TypeArguments
<>
ArgumentList:
Expression
ArgumentList , Expression
So, no, the Java language specification does not allow any shortcuts for making your anonymous class implement more interfaces than the type you're sub-typing.
If the class instance creation expression ends in a class body, then
the class being instantiated is an anonymous class. Then:
If T denotes an interface, then an anonymous direct subclass of Object
that implements the interface named by T is declared.
[...]
Let T be the type named by the Identifier and any type arguments. An
anonymous direct subclass of the class named by T is declared. The
body of the subclass is the ClassBody given in the class instance
creation expression.
Your alternative is the way to do it.
You can also use local classes.