JAVA logical operations

Question

I really don't understand this kind of "operations" or what are they called :

System.out.println((1<2) ?5: (3<4)   +   "   ");

Is the same with this code ?

if(1<2)
   return 5;
else if (3<4)

But after ':' it says Dead code . Why is that ?

Dead Code informs you about code that can't ever be reached. This is the case since 1 will always be smaller than 2. Please read alvinalexander.com/java/edu/pj/pj010018 to learn more about the ternary operator (that is what this construct is called) — reto
– reto, Commented Feb 15, 2015 at 11:21
See stackoverflow.com/questions/9987213/return-value-syntax-in-java/… — Qantas 94 Heavy
– Qantas 94 Heavy, Commented Feb 15, 2015 at 11:29

Sergey Kalinichenko · Accepted Answer · 2015-02-15 11:25:25Z

2

Compiler evaluates constant expressions at compile time. Because of that, the expression 1<2 is fully equivalent to the expression true, making the initial part of your conditional expression look like this:

System.out.println((true) ? 5 : (3<4)   +   "   ");
//                 ^^^^^^^^^^   ^^^^^
//        Important code          |
//                                |
//        Useless code -----------+

The compiler does not stop at evaluating 1<2, it goes on to evaluating the rest of the expression, which produces 5.

answered Feb 15, 2015 at 11:25

Sergey Kalinichenko

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Comments

Jimmy · Accepted Answer · 2015-02-15 11:22:52Z

0

Your code is weird, I really do not understand what are you trying to achieve. I think it is wrong, it should be like this:

return 1 < 2 ? 5 : 3 < 4 ? 1 : 2;

You can rewrite it into if-else form:

if (1 < 2)
    return 5;
if (3 < 4)
    return 1;
return 2;

Since return causes the program to jump out of function, else is not needed in this particular example.

answered Feb 15, 2015 at 11:22

Jimmy

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