Binding generic parameter to more than 1 type
suggest changeGeneric parameters can also be bound to more than one type using the T extends Type1 & Type2 & ...
syntax.
Let’s say you want to create a class whose Generic type should implement both Flushable
and Closeable
, you can write
class ExampleClass<T extends Flushable & Closeable> {
}
Now, the ExampleClass
only accepts as generic parameters, types which implement both Flushable
and Closeable
.
ExampleClass<BufferedWriter> arg1; // Works because BufferedWriter implements both Flushable and Closeable
ExampleClass<Console> arg4; // Does NOT work because Console only implements Flushable
ExampleClass<ZipFile> arg5; // Does NOT work because ZipFile only implements Closeable
ExampleClass<Flushable> arg2; // Does NOT work because Closeable bound is not satisfied.
ExampleClass<Closeable> arg3; // Does NOT work because Flushable bound is not satisfied.
The class methods can choose to infer generic type arguments as either Closeable
or Flushable
.
class ExampleClass<T extends Flushable & Closeable> {
/* Assign it to a valid type as you want. */
public void test (T param) {
Flushable arg1 = param; // Works
Closeable arg2 = param; // Works too.
}
/* You can even invoke the methods of any valid type directly. */
public void test2 (T param) {
param.flush(); // Method of Flushable called on T and works fine.
param.close(); // Method of Closeable called on T and works fine too.
}
}
Note:
You cannot bind the generic parameter to either of the type using OR (|
) clause. Only the AND (&
) clause is supported. Generic type can extends only one class and many interfaces. Class must be placed at the beginning of the list.
Found a mistake? Have a question or improvement idea?
Let me know.
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