Java 9 private interface methods

In Java SE 9 interfaces can have private and private static methods.

It was planned to have them yet in Java 8 SE, but was postponed due to other high priority features.
What’s the purpose of having private methods in interface? As we know in Java 8 interfaces can have default methods, so if between default methods needs to be shared code, private method can be used. Let’s see an example:

 

public interface Foo {

  default int max(List input) {
    List sorted = sort(input);
    return sorted.get(sorted.size() - 1);
  }

  default int min(List input) {
    List sorted = sort(input);
    return sorted.get(0);
  }

  private List sort(List input) {
    Collections.sort(input);
    return input;
  }
}
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