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Demonstrative Examples
Example 1:
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.
Example Language: Java (Bad)
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:
Example Language: (Good)
if (str1.equals(str2)) {
System.out.println("str1 equals str2");
}
Example 2:
In the example below, three JavaScript variables are declared and initialized with the same values.
Note that JavaScript will change a value between numeric and string as needed, which is the
reason an integer is included with the strings. An if statement is used to determine whether the
values are the same.
Example Language: JavaScript (Bad)
<p id="ieq3s1" type="text">(i === s1) is FALSE</p>
<p id="s4eq3i" type="text">(s4 === i) is FALSE</p>
<p id="s4eq3s1" type="text">(s4 === s1) is FALSE</p>
var i = 65;
var s1 = '65';
var s4 = new String('65');
if (i === s1)
{
document.getElementById("ieq3s1").innerHTML = "(i === s1) is TRUE";
}
if (s4 === i)
{
document.getElementById("s4eq3i").innerHTML = "(s4 === i) is TRUE";
}
if (s4 === s1)
{
document.getElementById("s4eq3s1").innerHTML = "(s4 === s1) is TRUE";
}
However, the body of the if statement will not be executed, as the "===" compares both the type
of the variable AND the value. As the types of the first comparison are number and string, it fails.
The types in the second are int and reference, so this one fails as well. The types in the third are
reference and string, so it also fails.
While the variables above contain the same values, they are contained in different types, so the
document.getElementById... statement will not be executed in any of the cases.
CWE Version 4.14
CWE-597: Use of Wrong Operator in String Comparison
CWE-597: Use of Wrong Operator in String Comparison