Because interfaces are static, public and don’t change, by definition any members you declare in them are static, public and final. Therefore you don’t need to qualify such members.

For example:

public interface A {
  String FOO = "foo";
}

is the same as:

public interface A {
  public final static String FOO = "foo";
}

You can read some more about this in the forum Interface member variable by default static?