Operator overloading in Java

Question

No, Java doesn't support user-defined operator overloading. The only aspect of Java which comes close to "custom" operator overloading is the handling of + for strings, which either results in compile-time concatenation of constants or execution-time concatenation using StringBuilder/StringBuffer. You can't define your own operators which act in the same way though.

For a Java-like (and JVM-based) language which does support operator overloading, you could look at Kotlin or Groovy. Alternatively, you might find luck with a Java compiler plugin solution.

Operator overloading is used in Java for the concatenation of the String type:

String concat = "one" + "two";

However, you cannot define your own operator overloads.

In addition to all the people pointing out that + is overloaded for Strings, - is also overloaded for both floating point and integer operations, as are * and /.

[edit] % is also overloaded for floating point, which can be a bit of a surprise for those with a C or C++ background.

Java does not allow operator overloading. The preferred approach is to define a method on your class to perform the action: a.add(b) instead of a + b. You can see a summary of the other bits Java left out from C like languages here: Features Removed from C and C++

As many others have answered: Java doesn't support user-defined operator overloading.

Maybe this is off-topic, but I want to comment on some things I read in some answers.

About readability.
Compare:

1. c = a + b
2. c = a.add(b)

Look again!
Which one is more readable?

A programming language that allows the creation of user-defined types, should allow them to act in the same way as the built-in types (or primitive types).

So Java breaks a fundamental principle of Generic Programming:
We should be able to interchange objects of built-in types with objects of user-defined types.
(You may be wondering: "Did he say 'objects of built-in'?". Yes, see here.)

About String concatenation:

Mathematicians use the symbol + for commutative operations on sets.
So we can be sure that a + b = b + a.
String concatenation (in most programming languages) doesn't respect this common mathematical notation.

a := "hello";
b := "world";
c := (a + b = b + a);

or in Java:

String a = "hello";
String b = "world";
boolean c = (a + b).equals(b + a);

Extra:
Notice how in Java equality and identity are confused. The == (equality) symbol means:
a. Equality for primitive types.
b. Identity-check for user-defined types, therefore, we are forced to use the function equals() for equality.
But... What has this to do with operator overloading?
If the language allows the operator overloading the user could give the proper meaning to the equality operator.