What is the difference between += and =+?

Question

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

Answer 1

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

Answer 2

=+ 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 3

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 4

+= 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 5

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 6

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.)