Name: dm26566 Date: 08/20/98


Arrays should provide their own implementations
for toString(), equals() and hashCode() instead
of the default implementations they inherit from
Object.

The toString() method should generate a comma
seperated list of the array elements enclosed in
square brackets. Primitive types should be converted
to strings using the appropriate conversion methods
and objects (including other arrays) should be
converted as if by String.valueOf(Object)

Examples:
[1, 2, 3] // array of ints
[a, b, c] // array of chars
[MyClass@ABCDEF, null, MyClass@123456] // array of MyClass objects
[] // empty array (zero length)
[[1, 2], [], [3], null] // array of arrays of ints

The equals() method should perform a value comparison
instead of a reference comparison. This will also
require that the hashCode() method be overridden
to return a value based on the array's contents.
I recommend using the formula given for
java.util.List.hashCode(). You'll have to modify
it to handle primitive types as well as object
references.
(Review ID: 37232)
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Name: jl125535 Date: 11/28/2001


java version "1.3.1"
Java(TM) 2 Runtime Environment, Standard Edition (build 1.3.1-b24)
Java HotSpot(TM) Client VM (build 1.3.1-b24, interpreted mode)

Another reason to support equals for array objects is to allow
java.util.Arrays.equals() to behave correctly when presented with arrays
of arrays.

According to the javadoc, java.util.Arrays.equals() is behaving properly.
In the code below, the unexpected behavior arises from the semantics
of the equals() method for objects that represent arrays.


Actual output:

Arrays.equals() = false
rows1.equals() = false


Expected output:

Arrays.equals() = true
rows1.equals() = true


Code:

import java.util.Arrays;

public class ArrayEqualityTest
{
    public static void main(String[] args)
    {
        String[][] rows1 = {
            new String[] { "4", "spank harder" },
            new String[] { "6", "douglas -- gangsta" },
            new String[] { "5", "momma''s revenge" }
        };

        String[][] rows2 = {
            new String[] { "4", "spank harder" },
            new String[] { "6", "douglas -- gangsta" },
            new String[] { "5", "momma''s revenge" }
        };

        System.out.println("Arrays.equals() = " + Arrays.equals(rows1, rows2));
        System.out.println("rows1.equals() = " + rows1.equals(rows2));
    }
}
(Review ID: 136372)
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