surprising double comparison

Question

I have messed with code execution result.

code:

System.out.println(0.2==0.1+0.1);
System.out.println(0.3==0.1+0.1+0.1);

output:

true
false

I know that 0.2 and 0.3 cannot transform to binary correct.

Why do I see different results?

UPDATE:

Can I predict result in similar issues without compiler?

Answer 1

PHP gave this:

<?php

printf("%0.20f\n", 0.1+0.1);
printf("%0.20f\n", 0.1+0.1+0.1);

?>
0.20000000000000001110
0.30000000000000004441

and

<?php
  echo 0.2==0.1+0.1?"true\n":"false\n";
  echo 0.3==0.1+0.1+0.1?"true\n":"false\n";
?>
true
false

The reaseon for the first to be "true":

<?php
   printf("%0.20f\n", 0.1+0.1);
   printf("%0.20f\n", 0.1+0.1+0.1);
   echo "\n";
   printf("%0.20f\n", 0.2);
   printf("%0.20f\n", 0.3);
?>

Output

0.20000000000000001110
0.30000000000000004441

0.20000000000000001110
0.29999999999999998890