Type conversion of int and string, java

Question

last exam we had the exercise to determine the output of the following code:

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

My answer was 5 >= 2 but now I realize that this is the wrong answer. It should be 5 >= 11 . But why?

Answer 1

Assuming that your syntax is :

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

expressions are evaluated from left to right, in this case 2 + 3 get summed to 5 and when "added" to a string result in "5 >=" , which when added to 1 gives "5 >= 1" , add another 1 and your result is: "5 >= 11"

Answer 2

Because "adding" a string to anything results in concatenation. Here is how it gets evaluated in the compilation phase:

((((2 + 3) + ">=") + 1) + 1)

The compiler will do constant folding, so the compiler can actually reduce the expression one piece at a time, and substitute in a constant expression. However, even if it did not do this, the runtime path would be effectively the same. So here you go:

((((2 + 3) + ">=") + 1) + 1) // original
(((5 + ">=") + 1) + 1)       // step 1: addition      (int + int)
(("5>=" + 1) + 1)            // step 2: concatenation (int + String)
("5>=1" + 1)                 // step 3: concatenation (String + int)
"5>=11"                      // step 4: concatenation (String + int)

You can force integer addition by sectioning off the second numeric addition expression with parentheses. For example:

System.out.println(2 + 3 + ">=" + 1 + 1);   // "5>=11"
System.out.println(2 + 3 + ">=" + (1 + 1)); // "5>=2"

Answer 3

Number+number=number
number+string=string
string+number=string
etc.

Answer 4

It is evaluated from left to right. You concatenate "1" to "5 >=" and finally "1" to "5 >= 1" .

Answer 5

Let's read it one token at a time from left to right:

The first literal encountered is an integer, 2 , then a + , then another integer, 3 . A + between two integers is addition, so they are added together to be 5 .

Now we have 5 , an integer, then a + , then a String ">=" . A + between an integer and a String is a concatenation operator. So the Strings are combined to form "5>=" .

Then we have "5>=" , a String, a + , and then an integer, 1 . This is String concatenation again. So the result is "5>=1" .

Finally we have "5>=1" , a String, a + , and the a 1 . his is String concatenation again. So the result is "5>=11" .