Conditional Ternary Operations

Question

First off, I came across this question recently and haven't being able to find a good explanation for it:

int x = (30 > 15)?(14 > 4) ? 1 : 0 : 2; 

I have used ternary expression before so I am familiar with them, to be honest I don't even know what to call this expression... I think that it breaks down like this

if (con1) or (con2) return 1         // if one is correct     
if (!con1) and (!con2) return 0      // if none are correct     
if (con1) not (con2) return 2        // if one but not the other

Like I said I don't really know so I could be a million miles away.

Answer 1

Because of operator precedence in Java, this code:

int x = (30 > 15)?(14 > 4) ? 1 : 0 : 2;

will be parsed as if it were parenthesized as follows:

int x = (30 > 15) ? ((14 > 4) ? 1 : 0) : 2;

(The only operators with lower precedence than ternary ?: are the various assignment operators: =, +=, etc.) Your code can be expressed verbally as:

• if (con1) and (con2) assign 1 to x
• if (con1) and (not con2) assign 0 to x
• otherwise assign 2 to x

EDIT: Nested ternary operators are often formatted in a special way to make the whole thing easier to read, particularly when they are more than two deep:

int x = condition_1 ? value_1     :
        condition_2 ? value_2     :
          .
          .
          .
        condition_n ? value_n     :
                      defaultValue; // for when all conditions are false

This doesn't work quite as cleanly if you want to use a ternary expression for one of the '?' parts. It's common to reverse the sense of a condition to keep the nesting in the ':' parts, but sometimes you need nesting in both branches. Thus, your example declaration could be rewritten as:

int x = (30 <= 15) ? 2 :
        (14 > 4)   ? 1 :
                     0 ;

Answer 2

It's int x = (30 > 15)?((14 > 4) ? 1 : 0): 2; :

if (30 > 15) {
    if (14 > 4) 
        x = 1;
    else 
        x = 0;
} else {
    x = 2;
}