Variable expected [duplicate]

Answer 1

The ++ operator only makes sense when applied to a declared variable.

This operator will add one to an integer, long, etc. and save the result to the same variable in-place.

If there is no declared variable, there is nowhere to save the result, which is why the compiler complains.

One way to allow use of the ++ operator in this situation would be (not the most concise code, but to illustrate the point):

int myVariable = this.answer.getPoints();
myVariable++;
this.answer.setPoints(myVariable);

Answer 2

Change this:

this.answer.setPoints((this.answer.getPoints())++);

to:

this.answer.setPoints((this.answer.getPoints())+1);

++ will increment a variable with 1, but since this.answer.getPoints() will return a value and its not a defined variable, it won't be able to store the incremented value.

Think of it like doing: this.answer.getPoints() = this.answer.getPoints() + 1, where would the incremented value be stored?

Answer 3

this.answer.getPoints() will return a value, and you can't use increment ++ or decrement -- on that. You can only use it on variables.

If you want to add 1 to it, you can do it as:

this.answer.setPoints((this.answer.getPoints())+1);

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I know that, but why?

You can do this:

int x = 5;
x++; // x is a variable and can have value 6

but not this:

5++; // 5 is a value and can't have value 6

Answer 4

The error is just in this bit:

(this.answer.getPoints())++

The first part of this (this.answer.getPoints()) creates an rvalue: effectively, an anonymous variable that lasts almost no time.

The second part ++ increments that anonymous variable after it is passed into setPoints().

Then, the anonymous variable (now incremented) is thrown away.

The compiler/IDE knows that you're doing something that will never be used (incrementing a temporary value), and is flagging it.