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The equals method
The equals method is defined in the Object class, and can be overridden in subclasses of Object . It is the responsibility of the author of the subclass to override the method so as to implement thatauthor's concept of "equal" insofar as objects of the class are concerned.
The overridden equals method
The reason that the equals method returned true in this case was that the author of the String class provided an overridden version of the equals method.
The default equals method
If the author of the class does not override the equals method, and the default version of the equals method inherited from Object is called on an object of the class, then according to Sun:
"for any reference values x and y, this method returns true if and only if x and y refer to the same object (x==y has the value true)"
In other words, the default version of the equals method inherited from the class Object provides the same behavior as the == operator when applied to object references.
C. Joe Joe false
The identity operator
This program illustrates the behavior of the == operator (sometimes referred to as the identity operator) when used to compare references to objects.
Two String objects with identical contents
As shown in the following fragment, this program instantiates two objects of the String class containing identical character strings.
class Worker{
void doIt(){char[] anArray = {'J','o','e'};String Str1 = new String(anArray);
String Str2 = new String(anArray); The fact that the two String objects contain identical character strings is confirmed by:
Compare object references using identity (==)
The references to the two String objects are compared using the == operator, and the result of that comparison is displayed. This comparison will produceeither true or false. The code to accomplish this comparison is shown in the following fragment.
System.out.println(
Str1 + " " + Str2 + " " +(Str1 == Str2)); The statement in the above fragment produces the following display:
Joe Joe false
How can this be false?
We know that the two objects are of the same type ( String ) and that they contain the same character strings. Why does the == operator return false?
Doesn't compare the objects
The answer lies in the fact that the above statement doesn't really compare the two objects at all. Rather, it compares the values stored in the referencevariables referring to the two objects. That is not the same as comparing the objects.
References are not equal
Even though the objects are of the same type and contain the same character string, they are two different objects, located in different parts of memory.Therefore, the contents of the two reference variables containing references to the two objects are not equal.
The correct answer is false
The == operator returns false as it should. The only way that the == operator could return true is if both reference variables refer to the same object, (which is not the case) .
The bottom line is ...
The == operator cannot be used to compare two objects for equality. However, it can be used to determine if two reference variables refer to the same object.
-end-
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