NullPointerException在空检查Java之后发生

Question

I have this if statement

if((check1==null||!check1.isSolid())&&(check2==null)||!check2.isSolid())

it throws a null pointer exception because check1 or check2 are null, but i don't understand why it is doing this, because i am checking for the null condition before i am accessing the object and if the object is null why would java bother checking isSolid because it would have already been true.

Answer 1

Your messed up your parenthesis. Java will group your statement together like this:

((check1 == null || !check1.isSolid()) && check2 == null) || !check2.isSolid()

If check1 is null and check2 , is null , the first statement will evaluate to true . The problem occurs when your move on to the second statement, since check2 is null , check2.isSolid() will through a NullPointerException .

Change your parenthesis to

(check1 == null || !check1.isSolid()) && (check2 == null || !check2.isSolid())

Answer 2

You mixed up the parentheses. Try:

if((check1==null||!check1.isSolid())&&(check2==null||!check2.isSolid()))

Answer 3

Try this:

boolean check1_result = (check1 == null) ? true : !check1.isSolid();
boolean check2_result = (check2 == null) ? true : !check2.isSolid();

if (check1_result && check2_result)
// do work...