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While this statement typically holds, it can be misleading as it does not account for instances that use values of static final fields initialized at a later stage. Even if a field is static final, it is not necessarily initialized before being read.
Noncompliant Code Example
This noncompliant code example contrives to calculate the account balance by subtracting the processing fee from the deposited amount, but fails to do so. The Cycle class object c is instantiated before the deposit field gets initialized.
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This statement asserts that the presence of a {{static}} field triggers the initialization of a class, however, in this example, a recursive attempt is being made to initialize the class already. Because such recursive attempts are ignored by the JVM, the default value of {{deposit}} is {{0}} during the initialization \[[Bloch 2005|AA. Bibliography#Bloch 05]\]. |
Compliant Solution
This compliant solution changes the initialization order of the class Cycle so that the fields meant to be used in computations get duly initialized.
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As initialization cycles can become insidious when many classes are involved, proper care must be taken to inspect the control flow.
Noncompliant Code Example
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This noncompliant code example uses an inner class that extends the outer class. The outer class in turn, uses the {{static}} instance of the inner class. This results in a circular initialization issue \[[Findbugs 2008|AA. Bibliography#Findbugs 08]\]. |
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|---|---|---|
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public class CircularClassInit {
static class InnerClassSingleton extends CircularClassInit {
static final InnerClassSingleton singleton = new InnerClassSingleton();
}
static final CircularClassInit foo = InnerClassSingleton.singleton;
}
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Compliant Solution
This compliant solution removes the instance of the inner class from the outer class.
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Notably, class initialization cycles can also occur because of circularity in the code present within the {{static}} initializers of two or more classes \[[Findbugs 2008|AA. Bibliography#Findbugs 08]\]. Also see the related guideline [MSC08-J. Avoid cyclic dependencies between packages]. |
Risk Assessment
Initialization cycles may lead to unexpected results.
Guideline | Severity | Likelihood | Remediation Cost | Priority | Level |
|---|---|---|---|---|---|
MSC07-J | low | unlikely | medium | P2 | L3 |
Automated Detection
TODO
Related Vulnerabilities
Search for vulnerabilities resulting from the violation of this guideline on the CERT website.
Other Languages
This guideline appears in the C++ Secure Coding Standard as DCL14-CPP. Avoid assumptions about the initialization order between translation units.
Bibliography
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\[[JLS 2005|AA. Bibliography#JLS 05]\] Sections [8.3.2.1, Initializers for Class Variables|http://java.sun.com/docs/books/jls/third_edition/html/classes.html#8.3.2.1]; [12.4, Initialization of Classes and Interfaces|http://java.sun.com/docs/books/jls/third_edition/html/execution.html#12.4] Puzzle 49: Larger Than Life \[[MITRE 2009|AA. Bibliography#MITRE 09]\] [CWE ID 665|http://cwe.mitre.org/data/definitions/665.html] "Improper Initialization" |
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