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javagenericsbinary-search

Do these two Java generic methods accept the same data types?

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!

Solution

  • 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.