What is the difference between += and =+?

Question

What is the difference between += and =+? Specifically, in java, but in general also.

Answer 1

i += 4;

means

i = i + 4;  // increase i by 4.

While

i =+ 4;

is equivalent to

i = +4;   // assign 4 to i. the unary plus is effectively no-op.

(See http://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html#jls-15.15.3 for what a unary + does.)

Answer 2

+= is an operator that increments the left-hand side of the assignment by the value of the right-hand side and assigns it back to the variable on the left-hand side. =+ is not an operator but, in fact, two operators: the assignment operator = and the unary plus + (positive) operator which denotes the value on the right-hand side is positive. It's actually redundant because values are positive unless they are negated with unary minus. You should avoid the =+ construct as it's more likely to cause confusion than do any actual good.

Answer 3

+= is get and increment:

a += 5; // adds 5 to the value of a

=+ isn't really a valid identifier on its own, but might show up when you're using the unary + operator:

a =+ 5; // assigns positive five to a

Answer 4

=+ is not an operator. The + is part of the number following the assignment operator.

int a = 4; int b = 4;

a += 1; b =+1;

System.out.println("a=" + a + ", b=" + b);

This shows how important it is to properly format your code to show intent.

Answer 5

+= is a way to increment numbers or String in java. E.g.

int i = 17;
i += 10;  // i becomes 27 now.

There is no =+ operator. But if you do i =+ 10; it means i is equal to +10 which is equal to just 10.

Answer 6

Specifically, in java, but in general also.

In Java x += <expr>; is equivalent to x = x + ( <expr> ); where the + operator may be the arithmetical add operator or the string concatenation operator, depending on the type of x. On the other hand, x =+ <expr>; is really an ugly way of writing x = + <expr>; where the + is unary plus operator ... i.e. a no-op for numeric types and a compilation error otherwise.

The question is not answerable in the general case. Some languages support a "+=" operator, and others don't. Similarly, some languages might support a "=+" operator and others won't. And some languages may allow an application to "overload" one or other of the operators. It simply makes no sense to ask what an operator means "in general".

Answer 7

I don't know what you mean by "in general", but in the early versions of C language (which is where most of Java syntax came from, through C++), =+ was the original syntax for what later became +=, i.e. i =+ 4 was equivalent to i = i + 4.

CRM (C Reference Manual) is the document the describes C language with =+, =-, =>> and so on.

Answer 8

When you have a+=b, that means you're adding b to whatever's already in a. If you're doing a=+b, however, you're assigning +b to a.

int a=2;
int b=5;
a+=b;
System.out.println(a); //Prints 7

a=2;
b=5;
a=+b;
System.out.println(a); //Prints 5