(ternary operator)三元运算符.

ternary operator:

　　advantage:

　　　　make a terse simple conditional assignment statement of if-then-else.

　　disadvantage:

　　　　if must contains return type,for instance,the code below compiles error.

 int a = 2 > 1 ? Print.println("2 > 1") : 1;
 //compile error.