SE450: Clone: clone() [6/32]

The intent is that

x.clone() != x

x.clone().getClass() == x.getClass()

x.clone().equals(x)

The last intent is not a requirement, but is generally true.

By convention, you obtain the returned object by calling super.clone(). If all superclasses do this, then x.clone().getClass() == x.getClass() will be true.

Object doesn't implement Cloneable itself. (Object.clone is protected.)

The Cloneable interface is meant to be a mixin interface, however it doesn't do a very good job of this.

Parts of Java that support cloning:

• the empty Cloneable interface (note the misspelling)
• The Object.clone method (or your superclass's clone method)
• CloneNotSupportedException, to signal the clone method shouldn't have been called.

You can:

• Support clone (implement Cloneable and declare clone() to throw no exceptions).
• Conditionally support clone (implement Clonable, but may throw CloneNotSupportedException). This is the case for a container class whose contents may or may not be clonable.
• Allow subclasses to support clone (do not implement Clonable; do nothing, or override clone to do the right thing for your class)
• Forbid clone (do not implement Clonable; override clone to always throw CloneNotSupportedException)