Description

Rationale: Code duplication makes maintenance more difficult, so it can be better to replace the multiple occurrences with a constant.

Properties

Examples

To configure the check:

<module name="Checker">
  <module name="TreeWalker">
    <module name="MultipleStringLiterals"/>
  </module>
</module>
        

Example:

public class Example1 {
  String a = "StringContents"; // violation, "StringContents" occurs twice
  String a1 = "unchecked";
  @SuppressWarnings("unchecked") // OK, duplicate strings are ignored in annotations
  public void myTest() {
    String a2 = "StringContents";
    String a3 = "DuoString" + "DuoString"; // violation, "DuoString" occurs twice
    String a4 = "SingleString";
    String a5 = ", " + ", " + ", "; // violation, ", " occurs three times
  }
}
        

To configure the check so that it allows two occurrences of each string:

<module name="Checker">
  <module name="TreeWalker">
    <module name="MultipleStringLiterals">
      <property name="allowedDuplicates" value="2"/>
    </module>
  </module>
</module>
        

Example:

public class Example2 {
  String a = "StringContents"; // OK, two occurrences are allowed
  String a1 = "unchecked";
  @SuppressWarnings("unchecked") // OK, duplicate strings are ignored in annotations
  public void myTest() {
    String a2 = "StringContents";
    String a3 = "DuoString" + "DuoString"; // OK, two occurrences are allowed
    String a4 = "SingleString";
    String a5 = ", " + ", " + ", "; // violation, three occurrences are NOT allowed
  }
}
        

To configure the check so that it ignores ", " and empty strings:

<module name="Checker">
  <module name="TreeWalker">
    <module name="MultipleStringLiterals">
      <property name="ignoreStringsRegexp"
        value='^(("")|(", "))$'/>
    </module>
  </module>
</module>
        

Example:

public class Example3 {
  String a = "StringContents"; // violation, "StringContents" occurs twice
  String a1 = "unchecked";
  @SuppressWarnings("unchecked") // OK, duplicate strings are ignored in annotations
  public void myTest() {
    String a2 = "StringContents";
    String a3 = "DuoString" + "DuoString"; // violation, "DuoString" occurs twice
    String a4 = "SingleString";
    String a5 = ", " + ", " + ", "; // OK, multiple occurrences of ", " are allowed
  }
}
        

To configure the check so that it flags duplicate strings in all syntactical contexts, even in annotations like @SuppressWarnings("unchecked"):

<module name="Checker">
  <module name="TreeWalker">
    <module name="MultipleStringLiterals">
      <property name="ignoreOccurrenceContext" value=""/>
    </module>
  </module>
</module>
        

Example:

public class Example4 {
  String a = "StringContents"; // violation, "StringContents" occurs twice
  String a1 = "unchecked"; // // violation, "unchecked" occurs twice
  @SuppressWarnings("unchecked")
  public void myTest() {
    String a2 = "StringContents";
    String a3 = "DuoString" + "DuoString"; // violation, "DuoString" occurs twice
    String a4 = "SingleString";
    String a5 = ", " + ", " + ", "; // violation, ", " occurs three times
  }
}
        

Example of Usage

• Checkstyle Style

Violation Messages

• multiple.string.literal

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