Operators and Assignments - Ternary Operator

Syntax

    operand1 ? operand2 : operand3

• also referred to as the conditional operator
• if operand1 is true, operand2 is returned, else operand3 is returned

       true ? op2 : op3             // op2 returned
      false ? op2 : op3             // op3 returned

• operand1 must be a boolean type
• operand1 can be an expression that evaluates to a boolean type

       (5 == 5) ? "yes" : "no"     // output: yes

• operand1 and operand2 must be promotable numeric types or castable object references, or null
• if one of operand2 or operand3 is a byte and the other a short, the type of the returned value will be a short

      byte = true ? byte : short  // found short, required byte

• if one of operand2 or operand3 is a byte, short or char and the other is a constant int value which will fit within the other operands range, the type of the returned value will be the type of the other operand

      short =  true ? short : 1000 // compiles and runs ok
      short = false ? short : 1000 // compiles and runs ok

• otherwise, normal binary numeric promotion applies
• if one of operand2 or operand3 is a null, the type of the return will be the type of the other operand
• if both operand2 and operand3 are different types, one of them must be compatible (castable) to the other type

Class_A a = new Class_A();
Class_B b = new Class_B();  // subclass of Class_A
Class_C c = new Class_C();
Class_A a1 = b;
Class_C c1;

c1 = false ? a : c;         // compile-error: incompatible types
a1 =  true ? b : a;         // returns class type of Class_B

Example Code

• TestTernary.java

Traps

• a non-boolean value or expression used for operand1