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copied!<p>Unfortunately I don't think this kind of "if Comparable do this else do that" logic is possible with the Java type system.</p> <p>You could split the Comparable and non-Comparable cases into separate classes and hide them behind an interface, something like this:</p> <pre><code>interface Interface<T> { public void processData(); } class MyClass<T> implements Interface<T> { private final Collection<? extends T> data; MyClass(Comparator<T> comparator, Collection<? extends T> data) { this.data = data; } public void processData() { // ... } } class MyCompClass<T extends Comparable<T>> implements Interface<T> { private final Collection<? extends T> data; MyCompClass(Collection<? extends T> data) { this.data = data; } public void processData() { // ... } } class Factory { static <T extends Comparable<T>> Interface<T> create(Collection<? extends T> data) { return new MyCompClass<T>(data); } static <T> Interface<T> create(Comparator<T> comparator, Collection<? extends T> data) { return new MyClass<T>(comparator, data); } } </code></pre> <p>But this might result in a lot of duplicated code. Another option is to leave MyClass requiring a Comparator in its constructor, and build that comparator in the factory:</p> <pre><code>class MyClass<T> { private final Collection<? extends T> data; MyClass(Comparator<T> comparator, Collection<? extends T> data) { this.data = data; } public void processData() { // ... } } class Factory { static <T extends Comparable<T>> MyClass<T> create(Collection<? extends T> data) { return new MyClass<T>(new Comparator<T>() { public int compare(T o1, T o2) { return o1.compareTo(o2); } }, data); } static <T> MyClass<T> create(Comparator<T> comparator, Collection<? extends T> data) { return new MyClass<T>(comparator, data); } } </code></pre>

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