What will be the output of the program?

class Q207 
{ 
    public static void main(String[] args) 
    {
        int i1 = 5; 
        int i2 = 6; 
        String s1 = '7'; 
        System.out.println(i1 + i2 + s1); /* Line 8 */
    } 
}

ANS:A - 18

This question is about the + (plus) operator and the overriden + (string cocatanation) operator. The rules that apply when you have a mixed expression of numbers and strings are: If either operand is a String, the + operator concatenates the operands. If both operands are numeric, the + operator adds the operands. The expression on line 6 above can be read as 'Add the values i1 and i2 together, then take the sum and convert it to a string and concatenate it with the String from the variable s1'. In code, the compiler probably interprets the expression on line 8 above as:

System.out.println( new StringBuffer() 
    .append(new Integer(i1 + i2).toString()) 
    .append(s1) 
    .toString() );