Comparison Using Wrong Factors

Description

This can lead to incorrect results and resultant weaknesses. For example, the code might inadvertently compare references to objects, instead of the relevant contents of those objects, causing two "equal" objects to be considered unequal.

Demonstrations

The following examples help to illustrate the nature of this weakness and describe methods or techniques which can be used to mitigate the risk.

Note that the examples here are by no means exhaustive and any given weakness may have many subtle varieties, each of which may require different detection methods or runtime controls.

Example One

In the example below, two Java String objects are declared and initialized with the same string values. An if statement is used to determine if the strings are equivalent.

String str1 = new String("Hello");
String str2 = new String("Hello");
if (str1 == str2) {
  System.out.println("str1 == str2");
}

However, the if statement will not be executed as the strings are compared using the "==" operator. For Java objects, such as String objects, the "==" operator compares object references, not object values. While the two String objects above contain the same string values, they refer to different object references, so the System.out.println statement will not be executed. To compare object values, the previous code could be modified to use the equals method:

if (str1.equals(str2)) {
  System.out.println("str1 equals str2");
}

See Also