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  1. JDK
  2. JDK-4103477

rfe: Need support for deep copying of Object

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    Details

    • Type: Enhancement
    • Status: Closed
    • Priority: P5
    • Resolution: Duplicate
    • Affects Version/s: 1.1.4, 1.1.5
    • Fix Version/s: None
    • Component/s: core-libs
    • Labels:
    • Subcomponent:
    • CPU:
      x86
    • OS:
      windows_nt

      Description



      Name: joT67522 Date: 01/12/98


      Given a generic container class whose contents
      are described in terms of Object:
      class GenericValue
      {
        Object value;
        ...
      }

      there is no way for this class to create a deep
      copy of an instance because Object.clone() cannot
      be invoked on value because of the protected
      attribute on clone(). Why isn't the CloneNotSupportedException sufficient protection
      and Object.clone public?


      This little program demonstrates the problem I am having:
      racs21:: tmp 46 > cat GenericArray.java

      class Int
      {
              int i;

              Int(int j)
              {
                      i = j;
              }
              int getIntValue()
              {
                      return i;
              }
              void setIntValue(int j)
              {
                      i = j;
              }
              public String toString()
              {
                      return "Int="+i;
              }
      }

      public class GenericArray
      {
              Object[] array;
              public GenericArray(int n)
              {
                      array = new Object[n];
              }
              public void insertElementAt(Object o, int n)
              {
                      if( n >= array.length )
                              throw new ArrayIndexOutOfBoundsException();
                      array[n] = o;
              }
              public Object elementAt(int n)
              {
                      if( n >= array.length )
                              throw new ArrayIndexOutOfBoundsException();
                      return array[n];
              }
              // Would like to make deep copy...?
              public GenericArray copy()
              {
                      GenericArray copy = new GenericArray(array.length);
                      for(int n = 0; n < array.length; n ++)
                              // copy.array[n] = array[n].clone(); this is not allowed
      but should be
                              copy.array[n] = array[n]; // Can only make a
      shallow copy
                      return copy;
              }


              public static void main(String[] args)
              {
                      Object[] numbers = {new Int(0), new Int(1), new Int(2), new
      Int(3)};
                      GenericArray array0 = new GenericArray(4);
                      for(int n = 0; n < numbers.length; n ++)
                              array0.insertElementAt(numbers[n], n);
                      // Should be able to make copy without affecting numbers[]
                      GenericArray array1 = array0.copy();
                      Int i = (Int) array1.elementAt(0);
                      i.setIntValue(10);
                      for(int n = 0; n < numbers.length; n ++)
                              System.out.println(n+", array1="+array1.elementAt(n)+",
      numbers="+numbers[n]);
              }
      }

      racs21:: tmp 47 > java GenericArray
      0, array1=Int=10, numbers=Int=10 // The i.setIntValue(10) changed numbers[0]
      1, array1=Int=1, numbers=Int=1
      2, array1=Int=2, numbers=Int=2
      3, array1=Int=3, numbers=Int=3
      racs21:: tmp 48 >


      Since I can't invoke clone() on a Object type, I cannot make an element
      by element deep copy of the Object[] array. I should be able to use
      the 'copy[n] = array[n].clone();' statement commented out above and
      allow a class to reject this by throwing a CloneNotSupportedException.
      Am I missing some obvious work around?


      (Review ID: 22777)
      ======================================================================

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              Assignee:
              jjb Josh Bloch
              Reporter:
              johsunw Joon Oh (Inactive)
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