Clone vs Copy constructor- which is recommended in java

Question

clone method vs copy constructor in java  which one is correct solution  where to use each case

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clone   was designed with several mistakes  see this question   so it s best to avoid it   From Effective Java 2nd Edition  Item 11  Override clone judiciously     Given all of the problems associated with Cloneable  it   s safe to say   that other interfaces should not extend it  and that classes   designed for inheritance  Item 17  should not implement it  Because of   its many shortcomings  some expert programmers simply choose never to   override the clone method and never to invoke it except  perhaps  to   copy arrays  If you design a class for inheritance  be aware that if   you choose not to provide a well-behaved protected clone method  it   will be impossible for subclasses to implement Cloneable    This book also describes the many advantages copy constructors have over Cloneable clone    They don t rely on a risk-prone extralinguistic object creation mechanism They don t demand unenforceable adherence to thinly documented conventions They don t conflict with the proper use of final fields They don t throw unnecessary checked exceptions They don t require casts    All standard collections have copy constructors  Use them   List lt Double gt  original      some list List lt Double gt  copy   new ArrayList lt Double gt  original

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Clone is broken  so dont use it      THE CLONE METHOD of the Object class   is a somewhat magical method that does   what no pure Java method could ever   do  It produces an identical copy of   its object  It has been present in the   primordial Object superclass since the   Beta-release days of the Java   compiler   and it  like all ancient   magic  requires the appropriate   incantation to prevent the spell from   unexpectedly backfiring   Prefer a method that copies the object  Foo copyFoo  Foo foo     Foo f   new Foo        for all properties in FOo   f set foo get       return f      Read more http   adtmag com articles 2000 01 18 effective-javaeffective-cloning aspx

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Keep in mind that the copy constructor limits the class type to that of the copy constructor  Consider the example      Need to clone person  which is type Person Person clone   new Person person     This doesn t work if person could be a subclass of Person  or if Person is an interface   This is the whole point of clone  is that it can can clone the proper type dynamically at runtime  assuming clone is properly implemented    Person clone    Person person clone      or  Person clone    Person SomeCloneUtil clone person      See Bozho s answer   Now person can be any type of Person assuming that clone is properly implemented

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Great sadness   neither Cloneable clone nor a constructor are great solutions   I DON T WANT TO KNOW THE IMPLEMENTING CLASS      e g  - I have a Map  which I want copied  using the same hidden MumbleMap implementation  I just want to make a copy  if doing so is supported   But  alas  Cloneable doesn t have the clone method on it  so there is nothing to which you can safely type-cast on which to invoke clone     Whatever the best  copy object  library out there is  Oracle should make it a standard component of the next Java release  unless it already is  hidden somewhere    Of course  if more of the library  e g  - Collections  were immutable  this  copy  task would just go away   But then we would start designing Java programs with things like  class invariants  rather than the verdammt  bean  pattern  make a broken object and mutate until good  enough

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Have in mind that clone   doesn t work out of the box  You will have to implement Cloneable and override the clone   method making in public   There are a few alternatives  which are preferable  since the clone   method has lots of design issues  as stated in other answers   and the copy-constructor would require manual work    BeanUtils cloneBean original  creates a shallow clone  like the one created by Object clone     this class is from commons-beanutils  SerializationUtils clone original  creates a deep clone   i e  the whole properties graph is cloned  not only the first level   from commons-lang   but all classes must implement Serializable Java Deep Cloning Library offers deep cloning without the need to implement Serializable

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See also  How to properly override clone method   Cloning is broken in Java  it s so hard to get it right  and even when it does it doesn t really offer much  so it s not really worth the hassle

[java] Clone() vs Copy constructor- which is recommended in java

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