Doubt in Sum Operator

**mnksingh94** · June 16th, 2014, 12:04 PM

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

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

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

Why??

**KevinWorkman** · June 16th, 2014, 12:25 PM

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);
 
	}
}

**Norm** · June 16th, 2014, 12:42 PM

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

**Cornix** · June 16th, 2014, 12:45 PM

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.

**KevinWorkman** · June 16th, 2014, 12:46 PM

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

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