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Thread: Doubt in Sum Operator

  1. #1
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    Lightbulb Doubt in Sum Operator

    ----------------------------------------------------IN JAVA---------------------------------------------------------------

    System.out.println('1'+"2"+2); System.out.println('1'+2+"2");

    The Output is:- The Output is:-
    122 512

    Why??


  2. #2
    Crazy Cat Lady KevinWorkman's Avatar
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    Default Re: Doubt in Sum Operator

    Because you're adding Strings, not numbers. Try running this test program to see it broken down into smaller steps:

    public class Test {
    	public static void main(String args[]){
     
    		char a = '1';
    		String b = "2";
    		int c = 3;
     
    		String x = a + b;
    		System.out.println(x);
    		x = x + c;
    		System.out.println(x);
     
    	}
    }
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  3. #3
    Super Moderator Norm's Avatar
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    Default Re: Doubt in Sum Operator

    There is an ambiguity with the usage of the + operator.
    For numeric operands, it adds their values: 3 + 4 => 7
    For Strings, it concatenates the Strings: "a" + "b" => "ab"

    The compiler treats char as numeric values:
    System.out.println((int)'1'); // 49
    so '1' + 2 => 51
    If you don't understand my answer, don't ignore it, ask a question.

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    Default Re: Doubt in Sum Operator

    Because of some hideous black compiler magic running in the background.
    You write:
    System.out.println('1'+2+"2");
    but what the compiler does with it is something like this:
    char a = '1';
    int b = 2;
    String c = "2";
    int d = ((int) a) + b;
    StringBuilder sb = new StringBuilder();
    sb.append(d):
    sb.append(c):
    String e = sb.toString();
    System.out.println(e);

    This happens for convenience, so that debugging is simpler and not as verbose, but it can be very confusing for beginners.
    I would personally really appreciate if the default compiler settings would not allow this, but I dont think anybody cares about my opinion on this.

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    Default Re: Doubt in Sum Operator

    Nice catch Norm. Looks like I missed half the point of the question. Doh!
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