UnusedLocalVariable
Since Checkstyle 9.3
Description
Checks that a local variable is declared and/or assigned, but not used. Doesn't supportpattern variables yet. Doesn't checkarray components as array components are classified as different kind of variables byJLS.
Properties
| name | description | type | default value | since |
|---|---|---|---|---|
| allowUnnamedVariables | Allow variables named with a single underscore (known as unnamed variables in Java 21+). | boolean | true | 10.18.0 |
Examples
To configure the check:
<module name="Checker"> <module name="TreeWalker"> <module name="UnusedLocalVariable"> </module> </module></module>Example:
class Example1 { { int k = 12; // violation, assign and update but never use 'k' k++; } int a; Example1(int a) { // ok, as 'a' is a constructor parameter not a local variable this.a = 12; } void method(int b) { int[] arr = {1, 2, 3}; // violation, unused named local variable 'arr' int[] anotherArr = {1}; // ok, 'anotherArr' is accessed anotherArr[0] = 4; } String convertValue(String newValue) { String s = newValue.toLowerCase(); // violation, unused named local variable 's' String _ = newValue.toLowerCase(); // ok, '_' is unnamed variable return newValue.toLowerCase(); } void read() throws IOException { BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); String s; // violation, unused named local variable 's' while ((s = reader.readLine()) != null) {} try (BufferedReader reader1 = // ok, 'reader1' is a resource new BufferedReader(new FileReader("abc.txt"))) {} try { } catch (Exception e) { } // ok, 'e' is an exception parameter } void loops() { int j = 12; for (int i = 0; j < 11; i++) // violation, unused named local variable 'i' for (int p = 0; j < 11; p++) p /= 2; // ok, 'p' is used for (Integer _ : new int[0]) { } // ok, '_' is unnamed variable } void lambdas() { Predicate<String> obj = (String str) -> true; // ok, 'str' is a lambda parameter obj.test("Test"); }}To configure the check to violate variables named with a single underscore if they are not used:
<module name="Checker"> <module name="TreeWalker"> <module name="UnusedLocalVariable"> <property name="allowUnnamedVariables" value="false"/> </module> </module></module>Example:
class Example1 { { int k = 12; // violation, assign and update but never use 'k' k++; } int a; Example1(int a) { // ok, as 'a' is a constructor parameter not a local variable this.a = 12; } void method(int b) { int[] arr = {1, 2, 3}; // violation, unused local variable 'arr' int[] anotherArr = {1}; // ok, 'anotherArr' is accessed anotherArr[0] = 4; } String convertValue(String newValue) { String s = newValue.toLowerCase(); // violation, unused local variable 's' String _ = newValue.toLowerCase(); // violation, unused local variable '_' return newValue.toLowerCase(); } void read() throws IOException { BufferedReader reader = new BufferedReader(new InputStreamReader(System.in)); String s; // violation, unused local variable 's' while ((s = reader.readLine()) != null) {} try (BufferedReader reader1 = // ok, 'reader1' is a resource new BufferedReader(new FileReader("abc.txt"))) {} try { } catch (Exception e) { } // ok, 'e' is an exception parameter } void loops() { int j = 12; for (int i = 0; j < 11; i++) // violation, unused local variable 'i' for (int p = 0; j < 11; p++) p /= 2; // ok, 'p' is used for (Integer _ : new int[0]) { } // violation, unused local variable '_' } void lambdas() { Predicate<String> obj = (String str) -> true; // ok, 'str' is a lambda parameter obj.test("Test"); }}Example of Usage
Violation Messages
All messages can be customized if the default message doesn't suit you. Pleasesee the documentation to learn how to.
Package
com.puppycrawl.tools.checkstyle.checks.coding