Boolean != false

Question

In Java, you would usually say that

if(someBool != false)

is the same as

if(someBool)

But what if someBool is not of type boolean but Boolean, and its value is null?

Solution 1

It will throw a NullPointerException (autounboxing of null throws NPE).

But that only means that you must not allow a null value. Either use a default, or don't use autounboxing and make a non-null check. Because using a null value of a boolean means you have 3, not 2 values. (Better ways of handling it were proposed by Michael and Tobiask)

Solution 2

If you want to handle Boolean instances as well as primitives and be null-safe, you can use this:

if(Boolean.TRUE.equals(someBool))

Solution 3

Use ApacheCommons BooleanUtils.isTrue() or .isFalse()

Solution 4

If someBool is Boolean

if (someBull != null && someBull) {
  //Yeah, true.
}

Since Boolean can be null make sure you avoid NullPointerException by checking for not null.

Solution 5

I did a little test:

    Boolean o = null;
    try {
        System.out.println(o ? "yes" : "no");
    } catch (Exception e) {
        e.printStackTrace();
    }
    try {
        System.out.println((o != false) ? "yes" : "no");
    } catch (Exception e) {
        e.printStackTrace();
    }

The output is surprising:

java.lang.NullPointerException
    at btest.main(btest.java:10)
java.lang.NullPointerException
    at btest.main(btest.java:15)

The first NPE is to be expected, because o will be autounboxed (and that fails because it's null). The second happens for the same reason, but it doesn't feel natural. Anyway, the solution is to do:

System.out.println(!Boolean.FALSE.equals(o) ? "yes" : "no");

View more solutions