You can use Wildcards in Generics to achieve the same. Your method signature would look like this:
public static void append(List<? extends Comparable> list)
Or even better and exactly the same meaning as your C# code:
public static <T> void append(List<? extends Comparable<T>> list, T value)
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…