Difference between += and =+ in java?

Question

I'm curious about one little thing. code like this:

    String test = "test";
    char[] test2 = {'a', 'i'};
    int i=0;
    test += test2[i] + "";
    System.out.println(test);

Works as we suspect, the output is "testa", but what is happening when we change operand "+=" to "=+"? Now the output is "97" and it's ascii code for an a letter, it's simple, but what happened with the whole string test? Thanks from advice.

http://stackoverflow.com/questions/4221225/converting-chars-to-ints-in-java/4221265#4221265 — Scott, Mar 31 '14 at 21:33

score 11 · Accepted Answer · edited May 23 '17 at 10:31

11

The "=+" version:

test =+ test2[i] + "";

is parsed as

test = (+test2[i]) + "";

The unary plus converts the char ('a') to an integer (its ASCII code, 97), which is then converted to a string ("97") by the concatenation with an empty string. The end result is the string "97".

edited May 23 '17 at 10:31

Community

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answered Mar 31 '14 at 21:30

NPE

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Ahh I see now. Thank you very much ^-^ – mlethys Mar 31 '14 at 21:33

Martijn Courteaux · Answer 2 · 2014-03-31T21:36:01.360

10

... += A means increase by A.
... =+ A means assign to positive A.

If you didn't notice the difference: a =+ b can be rewritten as: a = +b. There is no =+ operator. Where, in this case: +'a' gets converted to an int, because of the + operator.

edited Mar 31 '14 at 21:36

answered Mar 31 '14 at 21:29

Martijn Courteaux

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Yes, it basically just the same as `= 0+A;` – Kevin Sheehan Mar 31 '14 at 21:30
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It should be added that the ASCII code for the character 'a' is 97, which explains the OP's output. – Matt Logan Mar 31 '14 at 21:33

score 0 · Answer 3 · answered Mar 31 '14 at 21:32

As demonstrated here: https://ideone.com/fCtLyB

int CONST = 75;
int method1 = 5;
int method2 = 5;
method1 += CONST; //Adds the value to method1 variable
method2 =+ CONST; //Sets method2 variable to CONST
System.out.println(method1 + ", " + method2 + ", " + CONST);

It's like doing a=-5 which is really a=0-5, except here it's a=+5 or a=0+5.

score 0 · Answer 4 · answered Mar 31 '14 at 21:32

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+= is a common operator, you know what it means. On the other hand, when you put =+ you do an assigment and converting right side to integer, sto you get integer (97).

answered Mar 31 '14 at 21:32

vanste25

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Difference between += and =+ in java?

4 Answers4