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public final class MutableClass implements Cloneable {
  private Date date;
	
  public MutableClass(Date d) {
    this.date = new Date(d.getTime());  //copy-in 
  }
	
  public Date getDate() {
    return (Date)date.clone(); //copy and return
  }

  public Object clone() throws CloneNotSupportedException {
    final MutableClass cloned = (MutableClass)super.clone();
    cloned.date = (Date)date.clone();  //copy mutable Date object manually
    return cloned;
  }
}

Note that the clone() method must manually clone the Date object. This step is unnecessary for primitive fields and fields which refer to immutable objects.

A mutable class that defines a clone() method must be declared final. This ensures that untrusted code cannot subclass and override the clone() method to supply a spurious instance. The clone() method should copy all internal mutable state as necessary. In this compliant solution, the Date object is copied.

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