为什么不能在简短的IF语句中进行条件赋值？

Question

I'm trying to update softcount for my Blackjack game to account for Aces being played (value 11 or 1). When using the short-form IF statement, why is the first line of code incorrect, but the second line is okay to use? Is this type of if statement limited?

(counter > 1) ? (softcount+=1) : (softcount+=value); // bad


softcount += (counter > 1) ? 1 : value; // good

Answer 1

The ternary has to be seen as a way to evaluate something and not as a way to apply a processing.
So it expects some expressions after ? but you wrote statements : softcount+=1 and (softcount+=value) in the first code.
In the second code, it is ok because you specified two expressions : 1 and value .

Besides do you really find this code a short hand ?

(counter > 1) ? (softcount+=1) : (softcount+=value); // bad

You repeat the increment part.

What you want in your case is just :

if (counter > 1) { softcount+=1;} else {softcount+=value;)

Answer 2

It is simply how the language is defined.

Only certain expressions - statement expressions - can be made into a statement by adding ; . (Statement expression + ; is an expression statement ).

From JLS Sec 14.8 :

ExpressionStatement:
  StatementExpression ;

StatementExpression:
  Assignment 
  PreIncrementExpression 
  PreDecrementExpression 
  PostIncrementExpression 
  PostDecrementExpression 
  MethodInvocation 
  ClassInstanceCreationExpression

Conditional expressions are not statement expressions.

Answer 3

It is called ternary operator, it is used when you simply want to return a value based on condition. It's main purpose is to avoid if else for simple avaluations. In your case you should use if else.