understanding the java string with add operator

Question

I am trying to understand how the compiler views the following print statements. It is simple yet a bit intriguing.

This prints the added value. Convincing enough.<

Answer 1

I guess the Java specification explains it best:

The + operator is syntactically left-associative, no matter whether it is determined by type analysis to represent string concatenation or numeric addition. In some cases care is required to get the desired result. For example, the expression:

a + b + c

is always regarded as meaning:

(a + b) + c

So, if a was a String, then it concatenates with b. The result would be of String type, hence it continues to concatenate with c.

Answer 2

I also found this interesting. I haven't worked too much in java recently but I found out a little bit of info that might be helpful through playing with it.

I think this has to do with automatic Type-casting that java does.

System.out.println("1"+2+3);

Prints 123 as you said. Since "1" is casted as string, Java assumes since the first one was a string, the ones following will be a string for concatenation unless otherwise noted

Although, this result does print 15 when you define the type

System.out.println("1" + (int)(2+3));

In that case, it can complete the operation before concatenating.

So I think java is assuming if the first one is a String, that the rest are going to be strings and to concatenate them.

EDIT: you can see some info about automatic type-conversion on oracle's website here

Answer 3

The + operator is overloaded in the compiler. If both operands are numeric, + is addition. If either or both operands are String, + is string concatenation. (If one operand is String and the other is numeric, the number is cast to a String). Finally, + binds left-to-right.

All this causes a compound formula a + b + c + ... to do addition left-to-right until it hits the first string operand, at which point it switches to string concatenation for the remainder of the formula. So...

"1" + 2 + 3 + 4 = 1234   /* cat cat cat */
1 + "2" + 3 + 4 = 1234   /* cat cat cat */
1 + 2 + "3" + 4 = 334    /* add cat cat */
1 + 2 + 3 + "4" = 64     /* add add cat */

Answer 4

Thats interesting part of string. When a String is added to any other data type, the resultant value is a String.The other variable is also converted to a String and then concatenated. However, when two integers are operated with a + sign, the + acts as an addition operator and not a concatenation operator. If the expression within the println() or print() method contains parentheses, then the value within the parentheses is evaluated first. Consider the following example:

    int a = 5;
    int b = 6;
    System.out.println(a + b); // Output will be: 11
    System.out.println("5" + "6"); // Output will be: 56
    System.out.println("" + a + b); // Output will be: 56
    System.out.println(5 + 6 + a + " " + b + a); // Output will be: 16 65
    System.out.println("Result: " + a + b); // Output will be: 56
    System.out.println("Result: " + (a + b)); // Output will be: 11

You can see the difference between last two sysout statements