whats the difference between ".equals and =="

Question

i switched lecturers today and he stated using a weird code too me.

he says its better. when i asked why, he asnwered "because it is!"

so much for that.

so heres an example:

if (o1.equals(o2))
{
  System.out.println("Both integer objects are the same");
}

instead of what im used too:

if (o1 == o2)
{
  System.out.println("Both integer objects are the same");
}

whats the difference between the two. and why is his way better?

found this but i cant really make sense of that answer http://www.javabeat.net/qna/13-what-is-difference-between-equals-and-/

Answer 1

This has been asked many-a-time.

http://stackoverflow.com/questions/971954/difference-between-equals-and

Answer 2

In Java, == always just compares two references (for non-primitives, that is) - i.e. it tests whether the two operands refer to the same object.

However, the equals method can be overridden - so two distinct objects can still be equal.

For example:

String x = "hello";
String y = new String(new char[] { 'h', 'e', 'l', 'l', 'o' });

System.out.println(x == y); // false
System.out.println(x.equals(y)); // true

Answer 3

The == operator compares if the objects are the same instance. The equals() oerator compares the state of the objects (e.g. if all attributes are equal). You can even override the equals() method to define yourself when an object is equal to another.

Answer 4

If you and I each walk into the bank, each open a brand new account, and each deposit $100, then...

1. myAccount.equals(yourAccount) is true because they have the same value, but
2. myAccount == yourAccount is false because they are not the same account.

(Assuming appropriate definitions of the Account class, of course. ;-)