I am attempting to create a unsigned integer class.
public class UnsignedInteger extends Number implements Comparable<UnsignedInteger>
{
...
}
Is there a way to implement operators such as; +, -, *, /, <<, >>, |, ^, >>>, <<
Java does not support Operator Overloading. The only option you have is define methods like add(), subtract(), multiply(), etc, and write the logic there, and invoke them for particular operation.
You can have a look at BigInteger class to get an idea of how you can define methods to support various operations. And if interested, you can even go through the source code, that you can find in the src folder of your jdk home directory.
There are already 5 answers saying that you cannot overload operators, but I want to point out that you can not use arithmetical operators on objects at all. They only work with primitive types (int, double, etc).
The only reason the following code compiles
Integer a = 1, b = 2;
Integer c = a + b;
is because the Java compiler compiles it as
Integer a = Integer.valueOf(1), b = Integer.valueOf(2);
Integer c = Integer.valueOf(a.intValue() + b.intValue());
If you want this to work for your UnsignedInteger, you have to extend the javac (it is possible, though).
No you cannot override operators in Java.
It's not possible to override operators in Java. What you can do is define methods to represent the operations, like BigDecimal or BigInteger in the standard library do.
There is a javac-plugin (an annotation processor like Lombok) called "Java-OO", which adds operator overloading to Java.
It allows you to add operator overloading to your own classes very easily. In addition to this, many of the built-in classes of the Java API also supports operator overloading when using this plugin.
(For example: Instead of list.get(6) or map.get("hello") you can do list[6] and map["hello"])
All you need to do is to include the .jar on the classpath when compiling with javac.
There are plugins for all major IDEs: Eclipse, Netbeans and IntelliJ IDEA.
No. Java does not support operator overloading.
Java doesnt support operator overloading, they consider it a bad practice, knowing that they overloaded + and += operators for the String class
Related
I'm new to Java and I couldn't find an answer to it anywhere because i don't even know how to search for it.
I want to define how 2 objects can be added together, so you get a new one like for example you can add String "a" and String "b" to get "ab".
I know this can be done in python by doing self.__add__(self, other).
How can you do this in Java?
The thing you are looking for is called operator overloading. It exists in some languages, however in Java it does not.
The best thing you can do is to define a method add() inside the class and then use it like this:
object1.add(object2);
I know it looks nicer with a + between them, but that would make compiling more complex.
With the exception of java.lang.String being treated as a special case1, Java does not allow you to define the behaviour of + for arbitrary types, or indeed any other operator, as you can in some languages such as C++ or Scala. In other words, Java does not support operator overloading.
Your best bet is to build functions like add &c. Appeal to precedent here: see how the Java guys have done it with BigInteger, for example. Sadly there is no way of defining the precedence of your functions, so you have to use very many parentheses to tell the compiler how you want an expression to be evaluated. It's for this reason that I don't use Java for any serious mathematical applications as the implementation of even a simple equation quickly becomes an unreadable mess2.
1 Which in some ways does more harm than good: e.g. consider 1 + 2 + "Hello" + 3 + 4. This compile time constant expression is a string type with the value 3Hello34.
2 Note that C++ was used to model the gravitational lensing effects of the wormhole in the movie "Interstellar". I challenge anyone to do that in a language that does not support operator overloading! See https://arxiv.org/pdf/1502.03808v1.pdf
Java does not allow you to override operators. String is a special case that does allow this functionality.
What you can do is add an add function like so:
public YourObject add(YourObject yourObject){
return new YourObject(this.propertyToAdd + yourObject.propertyToAdd);
}
Though we all know that Java doesn't support operator overloading, then why is the + operator an arithmetic operator as well as String concatenation operator.
Can anybody explain this?
Java doesn't allow custom operator overloading. Several operators, not just +, are overloaded by specification, and that's the way they stay.
The main issue with custom operator overloading is the opaqueness and unpredictability of their semantics, contributing to the probability of massive WTF moments while reading (and even writing) code.
When we use + with strings, compiler actually convert them to use StringBuilder.
For instance why can I write the line
Character[] c = Arrays.sort(list.toArray(new Character[list.size()]))
But in documentation when I read about method referencing, they tell me to use :: instead? Doesn't it do the same as the . operator?
I dont know if the above code compiles, as I'm typing this on my mobile. Consider it a loose example.
The double colon operator is a new operator provided in Java8. It is syntactic sugar that tells the compiler to generate a lambda based on context which will call the method. This makes some lambda expression things a bit easier. Prior to Java8 this operator doesn't exist, and no, its not the same as the dot(.) operator. For example:
Math.max(4, 6) // Calls Math.max with the arguments 4 and 6
Math::max // A reference to the max method in the java.lang.Math class
For a bit of extra reading (Although this stuff is all in Beta and has not been officially released) try http://docs.oracle.com/javase/tutorial/java/javaOO/methodreferences.html
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.
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:
c = a + b
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.
You can't do this yourself since Java doesn't permit operator overloading.
With one exception, however. + and += are overloaded for String objects.
One can try Java Operator Overloading. It has its own limitations, but it worth trying if you really want to use operator overloading.
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 !
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.
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.
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.
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:
c = a + b
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.
You can't do this yourself since Java doesn't permit operator overloading.
With one exception, however. + and += are overloaded for String objects.
One can try Java Operator Overloading. It has its own limitations, but it worth trying if you really want to use operator overloading.
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 !
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.
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.