（浮点值+整数值+长值）如何产生意外结果？

Question

import java.util.*;
import java.lang.*;

class Main
{
    public static void main (String[] args) throws java.lang.Exception
    {
        Float f=new Float(3.1);
                Integer i=new Integer(1);
                long l=2;
                System.out.println("Result is "+l+f+i);
    }
}

Output : Result is 23.11

I saw the above code somewhere. I tried to find the reason behind such an unexpected output but no success. Please give some links or reference or explanation.

Additional Information: System.out.println(l+f+i+" is Result"); gives 6.1 is Result . That means order of string and numbers has effect on output.

Answer 1

This is String concatenation,

System.out.println("Result is "+l+f+i);

Gives

System.out.println("Result is "+"2"+"3.1"+"1");

Better group your arithmetic computation :

System.out.println("Result is "+(l+f+i));

You may find more details here : String Concatenation Operator +

Answer 2

You're not adding the number, you're printing them, because the default operation when placing an object in a System.out.println is to call his toString() method. So you're printing l.toString() + f.toString() + i.toString() .

if you want to display the sum, you have to use:

Float f=new Float(3.1);
Integer i=new Integer(1);
long l=2;
System.out.println("Result is "+ (l+f+i));

Answer 3

Concatenating a String with any number primitives or objects convert them to String with their toString() method :

System.out.println("Result is "+l+f+i); 

To perform the computation before the string concatenation, you should put the computation expression between parenthesis :

 System.out.println("Result is " + (l+f+i)); 

Answer 4

Adding an important point to the other answers here:

Whenever you do String concatenation, the toString() method is called for each elements in the concatenation. So, your elements to be concatenated are,

"Result is ", l, f, and i

For, primitives, Autoboxing would first convert them to Wrapper classes and toString() method of each would be called and that's what happened.