Operator overloading in Java

Question

Please can you tell me if it is possible to overload operators in Java? If it is used anywhere in Java could you please tell me about it.

Answer 1

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.

Answer 2

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.

Answer 3

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.

Answer 4

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++

Answer 5

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.

Answer 6

You can't do this yourself since Java doesn't permit operator overloading.

With one exception, however. + and += are overloaded for String objects.

Answer 7

One can try Java Operator Overloading. It has its own limitations, but it worth trying if you really want to use operator overloading.

Answer 8

Just use Xtend along with your Java code. It supports Operator Overloading:

    package com.example;

@SuppressWarnings("all")
public class Test {
  protected int wrapped;

  public Test(final int value) {
    this.wrapped = value;
  }

  public int operator_plus(final Test e2) {
    return (this.wrapped + e2.wrapped);
  }
}

package com.example

class Test2 {

    new() {
        val t1 = new Test(3)
        val t2 = new Test(5)
        val t3 = t1 + t2
    }

}

On the official website, there is a list of the methods to implement for each operator !

Answer 9

Or, you can make Java Groovy and just overload these functions to achieve what you want

//plus() => for the + operator
//multiply() => for the * operator
//leftShift() = for the << operator
// ... and so on ...

class Fish {
    def leftShift(Fish fish) {
        print "You just << (left shifted) some fish "
    }
}


def fish = new Fish()
def fish2 = new Fish()

fish << fish2

Who doesnt want to be/use groovy? :D

No you cannot use the compiled groovy JARs in Java the same way. It still is a compiler error for Java.

Answer 10

Unlike C++, Java does not support user defined operator overloading. The overloading is done internally in java.

We can take +(plus) for example:

int a = 2 + 4;
string = "hello" + "world";

Here, plus adds two integer numbers and concatenates two strings. So we can say that Java supports internal operator overloading but not user defined.