Java ternary operator (?:) doesn't work; second or third operand return boolean

Question

Can someone tell me why this use of the ternary operator is incorrect? Operands 2 and 3 return a boolean.

public class Something {
...
private static final d         


        

Answer 1

From JLS - Conditional Operator:

In fact, by the grammar of expression statements (§14.8), it is not permitted for a conditional expression to appear in any context where an invocation of a void method could appear.

Grammar of expression statements from JLS - 14.8:

Certain kinds of expressions may be used as statements by following them with semicolons:

ExpressionStatement:
      StatementExpression ;

StatementExpression:
       Assignment
       PreIncrementExpression
       PreDecrementExpression
       PostIncrementExpression
       PostDecrementExpression
       MethodInvocation
       ClassInstanceCreationExpression

An expression statement is executed by evaluating the expression; if the expression has a value, the value is discarded. Execution of the expression statement completes normally if and only if evaluation of the expression completes normally.

Unlike C and C++, the Java programming language allows only certain forms of expressions to be used as expression statements.

Now the way you are using the conditional operator is not a valid expression statement, as inferred from it's grammar. And hence you get the compiler error. You have to use it in any of the above mentioned context.

Answer 2

Usage of Java ternary operation condition should looks like

result = testCondition ? value1 : value2

it's java-language specification.

Equality, Relational, and Conditional Operators

In the following example, this operator should be read as: "If someCondition is true, assign the value of value1 to result. Otherwise, assign the value of value2 to result