Dereferenced variable is always null¶
ID: java/dereferenced-value-is-always-null
Kind: problem
Security severity:
Severity: error
Precision: very-high
Tags:
- reliability
- correctness
- exceptions
- external/cwe/cwe-476
Query suites:
- java-security-and-quality.qls
Click to see the query in the CodeQL repository
If a variable is dereferenced, and the variable has a null value on all possible execution paths leading to the dereferencing, the dereferencing is guaranteed to result in a NullPointerException.
A variable may also be implicitly dereferenced if its type is a boxed primitive type, and the variable occurs in a context in which implicit unboxing occurs. Note that the conditional operator unboxes its second and third operands when one of them is a primitive type and the other is the corresponding boxed type.
Recommendation¶
Ensure that the variable does not have a null value when it is dereferenced.
Example¶
In the following examples, the condition !dir.exists() is only executed if dir is null. The second example guards the expression correctly by using && instead of ||.
public void createDir(File dir) {
if (dir != null || !dir.exists()) // BAD
dir.mkdir();
}
public void createDir(File dir) {
if (dir != null && !dir.exists()) // GOOD
dir.mkdir();
}
References¶
The Java Tutorials: Autoboxing and Unboxing.
Java Language Specification: Conditional Operator ? :.
Common Weakness Enumeration: CWE-476.