Does calling clone on an array also clone its contents

Question

If I invoke clone   method on array of Objects of type A  how will it clone its elements  Will the copy be referencing to the same objects  Or will it call  element of type A  clone   for each of them

User · Answer

1D array of primitives does copy elements when it is cloned. This tempts us to clone 2D array(Array of Arrays).

Remember that 2D array clone doesn't work due to shallow copy implementation of clone().

public static void main(String[] args) {
    int row1[] = {0,1,2,3};
    int row2[] =  row1.clone();
    row2[0] = 10;
    System.out.println(row1[0] == row2[0]); // prints false

    int table1[][]={{0,1,2,3},{11,12,13,14}};
    int table2[][] = table1.clone();
    table2[0][0] = 100;
    System.out.println(table1[0][0] == table2[0][0]); //prints true
}

User · Answer

clone   creates a shallow copy  Which means the elements will not be cloned   What if they didn t implement Cloneable    You may want to use Arrays copyOf     for copying arrays instead of clone    though cloning is fine for arrays  unlike for anything else   If you want deep cloning  check this answer    A little example to illustrate the shallowness of clone   even if the elements are Cloneable   ArrayList   array   new ArrayList    new ArrayList    new ArrayList     ArrayList   clone   array clone    for  int i   0  i  lt  clone length  i           System out println System identityHashCode array i         System out println System identityHashCode clone i         System out println System identityHashCode array i  clone          System out println  -----        Prints   4384790   4384790 9634993   -----   1641745   1641745   11077203   -----

User · Answer

If I invoke clone   method on array of Objects of type A  how will it   clone its elements    The elements of the array will not be cloned      Will the copy be referencing to the same objects    Yes      Or will it call  element of type A  clone   for each of them    No  it will not call clone   on any of the elements

User · Answer

The clone is a shallow copy of the array   This test code prints     1  2     1  2   100  200     100  2    because the MutableInteger is shared in both arrays as objects 0  and objects2 0   but you can change the reference objects 1  independently from objects2 1    import java util Arrays                                                                                                                                    public class CloneTest                                                                                                                                        static class MutableInteger                                                                                                                                   int value                                                                                                                                                 MutableInteger int value                                                                                                                                      this value   value                                                                                                                                                                                                                                                                                               Override                                                                                                                                                 public String toString                                                                                                                                        return Integer toString value                                                                                                                                                                                                                                                                                                                                                                                                                                         public static void main String   args                                                                                                                         MutableInteger   objects   new MutableInteger                     new MutableInteger 1   new MutableInteger 2                                                             MutableInteger   objects2   objects clone                                                                                                                 System out println Arrays toString objects                                         Arrays toString objects2                                                                            objects 0  value   100                                                                                                                                    objects 1    new MutableInteger 200                                                                                                                       System out println Arrays toString objects                                         Arrays toString objects2

[java] Does calling clone() on an array also clone its contents?

Examples related to java

Examples related to clone