Variable expected [duplicate]

Answer 1

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