Question

The class Object defines an equal() method to compare objects.

Specify the advantages and disadvantages of using this method

and suggest an alternative for equality.

Illustrate with code examples.

(Please elaborate on the advantages and disadvantages; also please include your sources and references) Thanks a lot!

Answer 1

Consider this code:

String x = "Hello World";
String y = "Hello " + "World";
if (x == y)
System.out.println("The strings are ==");
if (x.equals(y))
System.out.println("The strings are equal");

The first will not print, but the second one will. This is because the two Strings are not the same object, even though they contain the same content.

The .equals() method, on the other hand, is smart enough to check the contents. It sees that both contain "Hello World" so it returns true.

If you did this:

String x = "Hello World";
String y = x;
if (x == y)
System.out.println("The strings are ==");

then it would print, because x and y would actually be the same object.

Here's the details as to why this is.

Deep down, if you have a primitive variable (like int), the value is stored in the variable. If you have int j = 8; then 8 is stored in the j variable. And if you then have int k = 8; then k will also have 8 stored in it. So if you use == on them, they will show as equal.

But if you have an object (like a String) then what is actually stored in the variable is a memory location which contains the rest of the object. So if you have String x = "Hello World"; then x does not *really* contain "Hello World" - it contains something like 0x13F70000, which is a memory location which then contains "Hello World". Then if you have String y = "Hello " + "World"; it's going to create a new memory location and also put "Hello World" in it. But now y is maybe 0x13F70040. It contains a different value than the x variable, so == will see them as not equal.

(And if you're wondering "well, why doesn't Java just share that memory location so both variables can use it" - sometimes it does, for Strings. That's known as string interning. So if you have String x = "Hello World"; and String y = "Hello World"; then the compiler might recognize that they are the same and cause them to use the same memory location, and == might return true.)

Alternative:

Using compare() method

In Java for locale specific comparison, one should use Collator class which is in java.text package. The one most important feature of Collator class is the ability to define our own custom comparison rules.

References- https://www.geeksforgeeks.org/java-equals-compareto-equalsignorecase-and-compare/