I'm new to Java and I'm trying to learn about generics. I tried to implement a simple version of binarySearch()
method that is also found in the Collections
class. I looked up the method signature and it's something like this:
public static <T> int binarySearch(List<? extends Comparable<? super T>> list, T key) {
// definition
}
I was wondering if the method above still accepts the same data types if you were to change the method definition to this:
public static <T extends Comparable<? super T>> int binarySearch(List<T> list, T key) {
// definition
}
If not, what are the differences between the two? Thank you!
Consider these classes:
class A extends Comparable<A> { /* ... */ }
class B extends A { /* ... */ }
Now define a key and a list with these types:
A key = new B();
List<B> list = List.of(key);
You can invoke the first form with these arguments, but not the second.
For example:
static class NonComparable {
}
static class MyComparable implements Comparable<NonComparable> {
@Override
public int compareTo(NonComparable o) {
return 0; // irrelevant for the example
}
}
And then declare the parameters:
List<MyComparable> list = Arrays.asList(new MyComparable());
NonComparable nonComparable = new NonComparable();
binarySearch(list, nonComparable);
One of your method definitions allows an invocation, the other does not.
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