Statements and Expressions in Java(The statement x = y = x = 0 is illegal??)

I am studying Java and am having a problem with the following question.

Which of these statements are true?

• a. Any expression can be used as a statement.
• b. The expression x++ can be used as a statement.
• c. The statement x = x + 5 is also an expression.
• d. The statement x = y = x = 0 is illegal.

The correct answers are b and c. However, I don't understand why those two are the answers. Can anybody explain it for me?

a

Take the expression a+1 for instance. This makes no sense as a statement as it does not change anything and is not possible.

b

x++ returns x and increments it afterwards.

As it changes the variable, it can be used as a statement.

c

When you assign a value to something else, it returns the assigned value.

d

This is possible because x=0 sets x to 0 and returns 0.

Then, it sets y to x (0) and returns this value (0).

Then, it sets x to y (0) (and returns this value (0)).