Java-syntax for explicitly specifying generic arguments in method calls
What is the syntax for explicitly giving the type paramet开发者_开发问答ers for a generic Java method?
The following is not the syntax
<ArgType>genericMethod()
It seems the type arguments must come after a dot as in
SomeClass.<ArgType>genericMethod()
this.<ArgType>genericMethod()
p.<ArgType>genericMethod()
super.<ArgType>genericMethod()
SomeClass.super.<ArgType>genericMethod()
SomeClass.this.<ArgType>genericMethod()
According to the Java specification that would be for example:
Collections.<String>unmodifiableSet()
(Sorry for asking and answering my own question - I was just looking this up for the third time. :-)
A good example from java.util.Collection
of specifying a generic method which defines its own generic type is Collection.toArray
where the method signature looks like:
<T> T[] toArray(T[] a);
This declares a generic type T, which is defined on method call by the parameter T[] a
and returns an array of T's. So the same instance could call the toArray method in a generic fashion:
Collection<Integer> collection = new ArrayList<Integer>();
collection.add(1);
collection.add(2);
// Call generic method returning Integer[]
Integer[] ints = collection.toArray(new Integer[]{});
// Call generic method again, this time returning an Number[] (Integer extends Number)
Number[] nums = collection.toArray(new Number[]{});
Also, see the java tutorial on generic type parameters.
精彩评论