Comparing java Strings with == [duplicate]

Question

Possible Duplicate:
Java String.equals versus ==

Is it possible to compare Java Strings using == operator?

Why do I often see, that equals() method is used instead?

Is it because when comparing with literal Strings (like "Hello") using == doesn't imply calling equals()?

Answer 1

== operator checks the bit pattern of objects rather than the contents of those objects, but equals function compare the contents of objects.

String str1=new String("abc");
String str2=new String("abc");

System.out.println(str1==str2); will return false because str1 and str2 are different object created with "new" . System.out.println(str1.equals(str2)) will return true because equals() checks for contents of object.

Answer 2

In Java, you cannot overload operators. The == operator does identity equality. The equals(...) method, on the other hand can be be overridden to do type-specific comparisons.

Here's a code snippet to demonstrate:

String a = "abcdef";
String b = a;
String c = new String(a);

println(a == b); // true
println(a.equals(b)); // true

println(a == c); // false
println(a.equals(c)); // true

The one complication is with equals(...) you need to care about null, too. So the correct null-safe idiom is:

(a == null ? b == null : a.equals(b))

This is a loop you don't have to jump through in say C#

Answer 3

To expand on @amit's answer, the == operator should only be used on value types (int, double, etc.) A String is a reference type and should therefore be compared with the .equals() method. Using the == operator on a reference type checks for reference equality in java (meaning both object references are pointing to the same memory location.)

Answer 4

No, it's not possible, because with == you compare object references and not the content of the string (for which you need to use equals).

Answer 5

Operator == compares for string object references ,whereas String.equals method checks for both object references + object values . Moreover , String.equals method inturn uses == operator inside its implementation.

Answer 6

== checks if the two objects refer to the same instance of an object, whereas equals() checks whether the two objects are actually equivalent even if they're not the same instance.