Never use assertions to validate arguments of public methods. According to the The Java Language Specification, §14.10, "The assert Statement" [JLS 20052015]:, states that
...assertions should not be used for argument - checking in public methods. Argument - checking is typically part of the contract of a method, and this contract must be upheld whether assertions are enabled or disabled.
Another A secondary problem with using assertions for argument checking is that erroneous arguments should result in an appropriate runtime run-time exception (such as
IllegalArgumentException,IndexOutOfBoundsException, orNullPointerException). An assertion failure will not throw an appropriate exception.
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The method getAbsAdd() computes and returns the sum of the absolute value of parameters x and y. It lacks argument validation, in violation of rule MET00-J. Validate method arguments. Consequently, it can produce incorrect results because of integer overflow or when either or both of its arguments are Integer.MIN_VALUE.
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This noncompliant code example uses assertions to validate arguments of a public method.:
| Code Block | ||
|---|---|---|
| ||
public static int getAbsAdd(int x, int y) {
assert x != Integer.MIN_VALUE;
assert y != Integer.MIN_VALUE;
int absX = Math.abs(x);
int absY = Math.abs(y);
assert (absX <= Integer.MAX_VALUE - absY);
return absX + absY;
}
|
...
This compliant solution validates the method arguments by ensuring that values passed to Math.abs() exclude Integer.MIN_VALUE and also by checking for integer overflow.:
| Code Block | ||
|---|---|---|
| ||
public static int getAbsAdd(int x, int y) {
if (x == Integer.MIN_VALUE || y == Integer.MIN_VALUE) {
throw new IllegalArgumentException();
}
int absX = Math.abs(x);
int absY = Math.abs(y);
if (absX > Integer.MAX_VALUE - absY) {
throw new IllegalArgumentException();
}
return absX + absY;
}
|
...
Using assertions to validate method arguments can result in inconsistent computations, runtime exceptions, and control flow vulnerabilities.
Rule | Severity | Likelihood | Remediation Cost | Priority | Level |
|---|---|---|---|---|---|
MET01-J | mediumMedium | probableProbable | mediumMedium | P8 | L2 |
Related Guidelines
Android Implementation Details
The assert statement is supported on the Dalvik VM but is ignored under the default configuration. Assertions may be enabled by setting the system property "debug.assert" via : adb shell setprop debug.assert 1 or by sending the command-line argument "--enable-assert" to the Dalvik VM.
Bibliography
Item 7. My assertions are not gratuitous, "My Assertions Are Not gratuitous" | |
[ESA 2005] | Rule 68. , Explicitly check method parameters for validity, and throw an adequate exception in case they are not valid. Do not use the assert statement for this purpose |
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