StringLiteralEquality
Since Checkstyle 3.2
Description
Checks that string literals are not used with
== or !=.
Since == will compare the object references, not the actual value of the strings,
String.equals() should be used.
More information can be found
in this article.
Rationale: Novice Java programmers often use code like:
if (x == "something")
when they mean
if ("something".equals(x))
Examples
To configure the check:
<module name="Checker">
<module name="TreeWalker">
<module name="StringLiteralEquality"/>
</module>
</module>
Examples of violations:
class Example1 {
String getName(){
return "Y";
}
void InvalidExample(){
String status = "pending";
// violation below, 'Literal Strings should be compared using equals(), not '==''
if (status == "done") {}
// violation below, 'Literal Strings should be compared using equals(), not '!=''
while (status != "done") {}
// violation below, 'Literal Strings should be compared using equals(), not '==''
boolean flag = (status == "done");
boolean flag1 = (status.equals("done"));
String name = "X";
if (name == getName()) {}
// ok, limitation that check cannot tell runtime type returned from method call
}
}
Example of Usage
Violation Messages
All messages can be customized if the default message doesn't suit you. Please see the documentation to learn how to.
Package
com.puppycrawl.tools.checkstyle.checks.coding