Testing for object equality by comparing the toString() representations of objects

Question

Following on from this question - how do you explain to someone that this is just crazy!:

boolean someMethod(Map<String, Object> context) {
    Object object = context.get("someProperty") 
    Object another = context.get("anotherProperty") 

    return object.toString().equals(another.toString());
}

Apparently the reason for why Object.equals(...) is not used is that "what's contained in the Map is not concretely known, but is definitely known to be one of the primitive wrappers i.e. String, Double, Boolean, etc... and that Boolean.TRUE is required to be equal(...) to the String "TRUE"".

Answer 1

It's wrong because there is no contract (not even an informal expectation!) for toString() that guarantees that any subclass of Object will define it in a way compatible with an equivalence relationship (read the javadoc for Object.equals() to see what I mean).

It may work for a class where you know that toString() is compatible with equals, but this is not the case for the values in Map<String, Object>!

For an obvious example where almost certainly the method doesn't do what you would expect, imagine a subclass of Object that does not override toString(). In that case, the String representation of your instance is a function of the class name and the object's hashCode. Almost certainly not what you want to use to test for equality.

Answer 2

It's just crazy, because it can go wrong, because string representations are not canonical:

Double zeroDouble = new Double(0);
Integer zeroInteger = new Integer(0);
zeroDouble.doubleValue() == zeroInteger.doubleValue(); // true
zeroDouble.toString().equals(zeroInteger.toString());  // false ("0.0" vs "0")

File file1 = new File("file.txt");
File file2 = new File("FILE.TXT");
file1.equals(file2);            // true in windows, false in unix
file1.toString().equals(file2); // false ("file.txt" vs. "FILE.TXT")

Answer 3

If you are keenly interested to know about Object Equality then use can use the method of class Object.

int hashCode() gives the integer value called hashCode which pertain to an object.

definitely the hashcode differs object to object.
     it's a easiest way to identify object equality.