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: 

String status = "pending";

if (status == "done") {} // violation

while (status != "done") {} // violation

boolean flag = (status == "done"); // violation

boolean flag = (status.equals("done")); // OK

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

Parent Module

TreeWalker