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This approach is useful when the instance fields are declared final. Callers request a copy by invoking the copy constructor with an existing MutableClass instance as its argument.

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This approach is useful when the instance fields are declared final.

Compliant Solution (clone())

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When a mutable class's instance fields are declared final and lack accessible copy methods, provide a clone() method, as shown in this compliant solution:

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Mutable classes that define a clone() method must be declared final.

Compliant Solution (Unmodifiable Date Wrapper)

If cloning or copying a mutable object is infeasible or expensive, one alternative is to create an unmodifiable immutable view class. This class overrides mutable methods to throw an exception, protecting the mutable class.

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Bibliography

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