Java 语法，用于在方法调用中显式指定泛型参数

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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. :-)

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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.

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最佳答案

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()