ERR50-JG. Use exceptions only for exceptional conditions

Exceptions should be used only to denote exceptional conditions. They should not be used for ordinary control flow purposes. Failure to follow this advice complicates both security analysis and debugging, can result in abnormal control flow, and can cause performance degradation.

Noncompliant Code Example

This noncompliant code example attempts to concatenate the string elements of the array values, storing the result as the first element.

String values[] = new String[3];
values[0] = "value1";
values[1] = "value2";
values[2] = "value3";
	
int i;
values[1] = null; // gets null value

try {
  i = 0;
  while(true) {	         
    values[0] = values[0].concat(values[i + 1]); // Concatenate and store in values[0]  
    i++;
  }
} catch (ArrayIndexOutOfBoundsException e) {
  i = 0; // Attempts to initialize i to 0
} catch (NullPointerException npe) {
  // Ignores
}

It uses an ArrayIndexOutOfBoundsException to detect the end of the array and reinitialize the value of variable i to 0 in the catch block. However, when some element of the array is null, a NullPointerException results. This exception is caught and ignored, a violation of guideline ERR08-J. Do not catch NullPointerException or any of its ancestors. Consequently, the variable i fails to be reinitialized.

The purpose of exception handling is to detect and recover from exceptional conditions rather than to transfer control flow. Further, the exception-based idiom is slower than the standard nonexceptional code. It also prevents optimizations that the Java Virtual Machine (JVM) would otherwise perform.

Compliant Solution

This compliant solution uses a standard for loop to concatenate the strings.

String values[] = new String[3];
values[0] = "value1";
values[1] = "value2";
values[2] = "value3";

int i;
for (i = 1; i < values.length; i++) {
  values[0] = values[0].concat(values[i]);
}
i = 0; // Initialize i to 0 after operation

Applicability

Use of exceptions for any purpose other than detecting and handling exceptional conditions complicates both security analysis and debugging and can cause performance degradation.

Bibliography

[Bloch 2001] Item 39: "Use exceptions only for exceptional conditions"
[JLS 2011] §11. Exceptions