Annotation Type AutoClone
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@Documented @Retention(RUNTIME) @Target(TYPE) public @interface AutoCloneClass annotation used to assist in the creation ofCloneableclasses. The@AutoCloneannotation instructs the compiler to execute an AST transformation which adds a publicclone()method and addsCloneableto the list of interfaces which the class implements.Because the JVM doesn't have a one-size fits all cloning strategy, several customizations exist for the cloning implementation. By default, the
clone()method will callsuper.clone()before callingclone()on eachCloneableproperty of the class.Example usage:
import groovy.transform.AutoClone
Which will create a class equivalent to the following:@AutoCloneclass Person { String first, last List favItems Date since }class Person implements Cloneable { ... public Person clone() throws CloneNotSupportedException { Person result = (Person) super.clone() result.favItems = favItems instanceof Cloneable ? (List) favItems.clone() : favItems result.since = (Date) since.clone() return result } ... }Which can be used as follows:def p = new Person(first:'John', last:'Smith', favItems:['ipod', 'shiraz'], since:new Date()) def p2 = p.clone() assert p instanceof Cloneable assert p.favItems instanceof Cloneable assert p.since instanceof Cloneable assert !(p.first instanceof Cloneable) assert !p.is(p2) assert !p.favItems.is(p2.favItems) assert !p.since.is(p2.since) assert p.first.is(p2.first)
In the above example,super.clone()is called which in this case callsclone()fromjava.lang.Object. This does a bit-wise copy of all the properties (references and primitive values). Properties likefirsthas typeStringwhich is notCloneableso it is left as the bit-wise copy. BothDateandArrayListareCloneableso theclone()method on each of those properties will be called. For the list, a shallow copy is made during itsclone()method.If your classes require deep cloning, it is up to you to provide the appropriate deep cloning logic in the respective
clone()method for your class.If one of your properties contains an object that doesn't support cloning or attempts deep copying of a data structure containing an object that doesn't support cloning, then a
CloneNotSupportedExceptionmay occur at runtime.Another popular cloning strategy is known as the copy constructor pattern. If any of your fields are
finalandCloneableyou should setstyle=COPY_CONSTRUCTORwhich will then use the copy constructor pattern. Here is an example making use of the copy constructor pattern:import groovy.transform.AutoClone import static groovy.transform.AutoCloneStyle.*
Which will create classes equivalent to the following:@AutoClone(style=COPY_CONSTRUCTOR)class Person { final String first, last final Date birthday }@AutoClone(style=COPY_CONSTRUCTOR)class Customer extends Person { final int numPurchases final List favItems }class Person implements Cloneable { ... protected Person(Person other) throws CloneNotSupportedException { first = other.first last = other.last birthday = (Date) other.birthday.clone() } public Person clone() throws CloneNotSupportedException { return new Person(this) } ... } class Customer extends Person { ... protected Customer(Customer other) throws CloneNotSupportedException { super(other) numPurchases = other.numPurchases favItems = other.favItems instanceof Cloneable ? (List) other.favItems.clone() : other.favItems } public Customer clone() throws CloneNotSupportedException { return new Customer(this) } ... }If you use this style on a child class, the parent class must also have a copy constructor (created using this annotation or by hand). This approach can be slightly slower than the traditional cloning approach but theCloneablefields of your class can be final. When using the copy constructor style, you can provide your own custom constructor by hand if you wish. If you do so, it is up to you to correctly copy, clone or deep clone the properties of your class.As a variation of the last two styles, if you set
style=SIMPLEthen the no-arg constructor will be called followed by setting the individual properties (and/or fields) callingclone()if the property/field implementsCloneable. Here is an example:import groovy.transform.AutoClone import static groovy.transform.AutoCloneStyle.*
Which will create classes equivalent to the following:@AutoClone(style=SIMPLE)class Person { final String first, last final Date birthday }@AutoClone(style=SIMPLE)class Customer { final List favItems }class Person implements Cloneable { ... public Person clone() throws CloneNotSupportedException { def result = new Person() copyOrCloneMembers(result) return result } protected void copyOrCloneMembers(Person other) { other.first = first other.last = last other.birthday = (Date) birthday.clone() } ... } class Customer extends Person { ... public Customer clone() throws CloneNotSupportedException { def result = new Customer() copyOrCloneMembers(result) return result } protected void copyOrCloneMembers(Customer other) { super.copyOrCloneMembers(other) other.favItems = favItems instanceof Cloneable ? (List) favItems.clone() : favItems } ... }You would typically use this style only for base classes where you didn't want the normalObjectclone()method to be called and you would typically need to use theSIMPLEstyle for any child classes.As a final example, if your class already implements the
SerializableorExternalizableinterface, you can choose the following cloning style:
which outputs a class with the following form:@AutoClone(style=SERIALIZATION)class Person implements Serializable { String first, last Date birthday }class Person implements Cloneable, Serializable { ... Person clone() throws CloneNotSupportedException { def baos = new ByteArrayOutputStream() baos.withObjectOutputStream{ it.writeObject(this) } def bais = new ByteArrayInputStream(baos.toByteArray()) bais.withObjectInputStream(getClass().classLoader){ (Person) it.readObject() } } ... }This will output an error if your class doesn't implement one ofSerializableorExternalizable, will typically be significantly slower than the other approaches, also doesn't allow fields to be final, will take up more memory as even immutable classes like String will be cloned but does have the advantage that it performs deep cloning automatically.Further references on cloning:
- Since:
- 1.8.0
- See Also:
AutoCloneStyle,ExternalizeMethods
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Optional Element Summary
Optional Elements Modifier and Type Optional Element Description java.lang.String[]excludesComma separated list of property (and/or field) names to exclude from cloning.booleanincludeFieldsInclude fields as well as properties when cloning.AutoCloneStylestyleStyle to use when cloning.
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Element Detail
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excludes
java.lang.String[] excludes
Comma separated list of property (and/or field) names to exclude from cloning. For convenience, a String with comma separated names can be used in addition to an array (using Groovy's literal list notation) of String values.NOTE: When using the
CLONEstyle, property (and/or field) copying might occur as part of callingsuper.clone()which will ignore this list. You can then use this list to streamline the providedclone()implementation by selecting which Cloneable properties (and/or fields) will have a subsequent call to theirclone()method. If you have immutable properties (and/or fields) this can be useful as the extraclone()will not be necessary and cloning will be more efficient.NOTE: This doesn't affect property (and/or field) copying that might occur as part of serialization when using the
SERIALIZATIONstyle, i.e. this flag is ignored; instead adjust your serialization code to include or exclude the desired properties (and/or fields) which should carry over during cloning.- Default:
- {}
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includeFields
boolean includeFields
Include fields as well as properties when cloning.NOTE: When using the
CLONEstyle, field copying might occur as part of callingsuper.clone()and might be all you require; if you turn on this flag, the providedclone()implementation will also subsequently callclone()for eachCloneablefield which can be useful if you have mutable fields.NOTE: This doesn't affect field copying that might occur as part of serialization when using the
SERIALIZATIONstyle, i.e. this flag is ignored; instead adjust your serialization code to include or exclude your fields.- Default:
- false
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style
AutoCloneStyle style
Style to use when cloning.- Default:
- groovy.transform.AutoCloneStyle.CLONE
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