I have a class like this:
private static class Num {
private int val;
public Num(int val) {
this.val = val;
}
}
Is it possible to add to objects of the class by using the "+"-operator?
Num a = new Num(18);
Num b = new Num(26);
Num c = a + b;
No, you can't. + is overloaded only for numbers, chars and String, and you are not allowed to define any additional overloadings.
There is one special case, when you can concatenate any objects' string representation - if there is a String object in the first two operands, toString() is called on all other objects.
Here's an illustration:
int i = 0;
String s = "s";
Object o = new Object();
Foo foo = new Foo();
int r = i + i; // allowed
char c = 'c' + 'c'; // allowed
String s2 = s + s; // allowed
Object o2 = o + o; // NOT allowed
Foo foo = foo + foo; // NOT allowed
String s3 = s + o; // allowed, invokes o.toString() and uses StringBuilder
String s4 = s + o + foo; // allowed
String s5 = o + foo; // NOT allowed - there's no string operand
String object somewhere - not somewhere. It must be one of the first two operands, since a+b+c parses as (a+b)+c and the plus works only if at least one of the two operands is declared as a String. That's why o+o+s doesn't compile while the other two permutations do.
No, because James Gosling said so:
I left out operator overloading as a fairly personal choice because I had seen too many people abuse it in C++.
Source: http://www.gotw.ca/publications/c_family_interview.htm
Reference: Why doesn't Java offer operator overloading?
No. Java does not support operator overloading (for user-defined classes).
There is no operators overloading in java. The only thing which is supported for objects, is string concatenations via "+". If you have a sequences of objects joined via "+" and at least one of them is a String, then the result will be inlined to String creation. Example:
Integer a = 5;
Object b = new Object();
String str = "Test" + a + b;
will be inlined to
String str = new StringBuilder("Test").append(a).append(b).toString();
+ is a special case for strings, just to make life easier. The compiler replaces string concats with string buildersNo, it is not possible, as Java doesn't support operator overloading.
