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Operator overloading in Java
(10 answers)
How does the String class override the + operator?
(7 answers)
Closed 6 years ago.
Everywhere on the internet i found that java doesn't support Operator overloading but i am confused somehow.Because if that is so then how is the "+" operator able to add both constants and strings?
Any explanation would be appreciated
A language is said to support operator overloading when you can overload operators, i.e. make them do something that is not built into the language. Not when the langauge uses the same operator for two different things.
You can use these operators because it was implemented in the language how they behave. But there is no support for operator overloading in java.
You can create methods such as add(Object o) which is basically the same as what operators do except that it doesn't look as good.
Some languages, such as C#, allow you to overload the operators. In other words, you can define what is meant by == or ++, etc. This can be very useful in scenarios where you wish to use == to test for equality of objects instead of using a .equals() method, for instance.
Here's a tutorial for C#, which shows you how to do it with a + operator:
http://www.tutorialspoint.com/csharp/csharp_operator_overloading.htm
Or this:
https://msdn.microsoft.com/en-us/library/aa288467(v=vs.71).aspx
And you can't do this in Java at present.
Related
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Multiple lambda method references
(3 answers)
Closed 5 years ago.
list.stream().forEach(e -> method(e)) can be converted to list.stream().forEach(this::method)
Similarly can we convert list.stream().forEach(e -> { method1(e); method2(e);}); using method references expressions. Big apologies if you don't understand question. I am using mobile app first time.
No you cannot.
The point of Method references in Java is to abstract (syntaxically) a lambda expression. Since forEach consumes a function that takes 1 element of type specified by the parent stream, there is no syntax sugar for double application using method references.
Even I'm not sure that this answer is wanted by you,
How about changing the method to static one in that class?
This question already has answers here:
"+" operator for Java-classes
(5 answers)
Closed 5 years ago.
I'm trying to make a java library with a bunch of extra classes, and I was adding one for Imaginary numbers. Is there any way in java to make a custom class that is affected by mathematics operations
for example
Imaginary(10) * Imaginary(50) = "500i"
No, it is not possible to define custom arithmetic operators that overload default operators, but you can create methods like Imaginary.mutiply(Imaginary i).
You cannot overload operators in Java. See this previous answer to a similar question: https://stackoverflow.com/a/5883909/1701316
Your class will need to implement its operations as methods. If you'd like, since any character is allowed in a method name, you can name them with the typical operators, but they'll still need to be called with dot-notation: Imaginary(10).*(Imaginary(50))
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.
Java is a Strong Static Casting so does that mean there is no use for "==="
I have looked at tons of documentation and have not seen Identical Comparison Operator.
=== is useful in weak typed languages, such as Javascript, because it verifies that the objects being compared are of the same type and avoids implicit conversions.
=== has absolutely no use in a strongly typed language such as Java because you can't compare variables of different types without writing a specific method for doing this.
For example, if you want to compare an int to a String in Java, you will have to write some special method as such:
boolean compareIntString(int i, String s) {
return (i == parseInt(s));
}
But this is pretty much overkill. (And as you'll notice, as written, this method only accepts an int and a String. It doesn't accept just any two variables. You know before you call it that the datatypes are different.)
The main point is, that while you can do i == s in Javascript, you can't do i == s in Java, so you don't need ===.
I guess, the short answer is that Java's == is Javascript's ===. If you want to emulate Javascript's == and compare two items, ignoring data type, you'll have to write a custom method which accepts generic data types as arguments... and figure out the logic on comparing, at a minimum, all the possible combinations of Java's primitive data types...
No java does not have === operator. Reason is pretty well explained by nhgrif. Here is the list of operators in java and their precedence:
Source: http://docs.oracle.com/javase/tutorial/java/nutsandbolts/operators.html
I program in Java and have been trying to understand exactly what operator overloading is. I'm still a bit puzzled.
An operator can take on different meanings depending on which class uses it? I've read that it is "Name Polymorphism".
Java apparently does not support it and there seems to be a lot of controversy around this. Should I worry about this?
As a last question, in an assignment the teacher has stated that the assignment uses operator overloading, he is a C++ programmer mainly but we are allowed to write the assignment in Java. since Java does not support overloading, is there something I should be wary of?
Operator overloading basically means to use the same operator for different data types. And get different but similar behaviour because of this.
Java indeed doesn't support this but any situation where something like this could be useful, you can easily work around it in Java.
The only overloaded operator in Java is the arithmetic + operator. When used with numbers (int, long, double etc.), it adds them, just as you would expect. When used with String objects, it concatenates them. For example:
String a = "This is ";
String b = " a String";
String c = a + b;
System.out.print (c);
This would print the following on the screen: This is a String.
This is the only situation in Java in which you can talk about operator overloading.
Regarding your assignment: if the requirement is to do something that involves operator overloading, you can't do this in Java. Ask your teacher exactly what language you are allowed to use for this particular assignment. You will most likely need to do it in C++.
PS: In case of Integer, Long, Double etc. objects, it would also work because of unboxing.
Java doesn't allow overloading operators. It uses a very limited kind of operator overloading though, since + does addition or concatenation depending on the context.
If your assignment asks you to implement something by overloading operators, you won't be able to do it in Java. Maybe you should ask the teacher why he allows Java for such an assignment.
If your assignment only asks you to use an overloaded operator, then having your program use + for concatenation and addition would fit the bill. But I would ask the teacher, because I doubt that it's what he expects.
Java apparently does not support it and there seems to be a lot of
controversy around this.
There is no controversy about this. Some people might disagree with the decision, but James Gosling and others decided from day one to leave operator overloading by class developers out of the language. It's not likely to change.
As pointed out by others here, they reserved the right for the JVM to overload operators on a limited basis. The point is that you can't do it when you're developing your own classes.
They did it because there were examples of C++ developers abusing the capability (e.g. overloading the dot operator.)
Should I worry about this?
No. Java won't explode. You just won't be able to do it for your classes. If you feel like you need to, you'll just have to write C++ or some other language.
As to your query about the difference between operator overloading and polymorphism. Polymorphism is a standard OOP concept where an instance of a class may exhibit different characteristics depending on the underlying type. For example in C++:
class Shape {
...
virtual void draw()=0;
}
class Circle :public Shape {
virtual void draw() {...draw a circle...}
}
class Square:public Shape {
virtual void draw() {...draw a square...}
}
..
Shape *s = new Circle();
s->draw(); // calls Circle::draw();
s=new Square(); // calls Square::draw();
Hence s is exhibiting polymorphism.
This is different from operator overloading but you already have been explained what that is in the other answers.
Can either use natural a != b (a is not equal to b) or a.Equals(b)
b.set(1, 0);
a = b;
b.set(2, 0);
assert( !a.Equals(b) );
But java has a limited set of operator overloading than other languages http://en.wikipedia.org/wiki/Operator_overloading