Description Holger Klene 2012-07-21 10:31:36 EDT

Build Identifier: Version: 4.2.0 Build id: I20120608-1400

Have a look at the example method.

The check if (unknown == null) sheds doubt on unknown, which manifests in a Potential null pointer access (=PNPA) below.

Copying the very same block above the check will go unnoticed.

In addition modifying the check to:
if (b && unknown == null) or
if (!b && unknown == null)
will swallow the PNPA while
if (unknown == null && b) or
if (unknown == null && !b)
both preserve it. I wonder if short-circuiting boolean expression could be suppressed for gathering null-info, as b may or may not depend on the nullness. Naively I consider the check against null as a deliberately placed warning sign.

It would be great, if the first dereference in a method could be flagged, possibly hinting, that a nullcheck follows. The other way round may also be worthwile to flag the nullcheck as "Potentially dead code, as the variable may have been dereferenced before."

Reproducible: Always

Steps to Reproduce:
public void someMethod(final Object unknown, final boolean b) {
    if (b) {
        // No Warning/Error here :-(
        unknown.toString();
    }

    if (unknown == null) {
        System.out.println("is null");
    }

    if (b) {
        // Potential null pointer access:
        // The variable unknown may be null at this location
        unknown.toString();
    }
}