EmptyBlock

Since Checkstyle 3.0

Description

Checks for empty blocks.

This check does not validate sequential blocks. This check does not violate fallthrough.

NOTE: This check processes LITERAL_CASE and LITERAL_DEFAULT separately. Verification empty block is done for single nearest {@code case} or {@code default}.

Properties

name description type default value since
option Specify the policy on block contents. BlockOption statement 3.0
tokens tokens to check subset of tokens LITERAL_WHILE , LITERAL_TRY , LITERAL_CATCH , LITERAL_FINALLY , LITERAL_DO , LITERAL_IF , LITERAL_ELSE , LITERAL_FOR , INSTANCE_INIT , STATIC_INIT , LITERAL_SWITCH , LITERAL_SYNCHRONIZED , LITERAL_CASE , LITERAL_DEFAULT , ARRAY_INIT . LITERAL_WHILE , LITERAL_TRY , LITERAL_FINALLY , LITERAL_DO , LITERAL_IF , LITERAL_ELSE , LITERAL_FOR , INSTANCE_INIT , STATIC_INIT , LITERAL_SWITCH , LITERAL_SYNCHRONIZED . 3.0

Examples

To configure the check: 

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

Example:

public class Example1 {
  private void emptyLoop() {
    for (int i = 0; i < 10; i++) { // violation 'Must have at least one statement'
    }

    try { // violation 'Must have at least one statement'

    } catch (Exception e) {
      // ignored
    }
  }
}

To configure the check for the text policy and only try blocks: 

<module name="Checker">
  <module name="TreeWalker">
    <module name="EmptyBlock">
      <property name="option" value="text"/>
      <property name="tokens" value="LITERAL_TRY"/>
    </module>
  </module>
</module>

Example:

public class Example2 {
  private void emptyLoop() {
    for (int i = 0; i < 10; i++) {
      // ignored
    }

    try {
    }  // violation above 'Empty try block'
    catch (Exception e) {
      // ignored
    }
  }
}

To configure the check for case and default in switch block: 

<module name="Checker">
  <module name="TreeWalker">
    <module name="EmptyBlock">
      <property name="tokens" value="LITERAL_CASE,LITERAL_DEFAULT"/>
    </module>
  </module>
</module>

Example:

public class Example3 {

  private void testBadSwitchStatement(int a) {
    switch (a) {
      case 1 : { }  // violation, 'Must have at least one statement'
      // the second empty block is 'sequential', skipped.
      // violation below, 'Must have at least one statement'
      case 2: {} {};
      // violation below, 'Must have at least one statement'
      case 3: {} {System.out.println();}
      // the second empty block is 'sequential', skipped.
      case 4: {System.out.println();} {}
      default : { }  // violation, 'Must have at least one statement'
    }
  }

  private void testGoodSwitchStatement(int a) {
    switch (a) {
      case 1: { someMethod(); }
      default: { someMethod(); }
    }
    switch (a) {
      case 1: { someMethod(); }
      default: // OK, as there is no block
    }
  }

  private void testBadSwitchRule(int a) {
    switch (a) {
      case 1 -> { } // violation, 'Must have at least one statement'
      default -> { } // violation, 'Must have at least one statement'
    }
  }

  private void testGoodSwitchRule(int a) {
    switch (a) {
      case 1 -> { someMethod(); }
      default -> { someMethod(); }
    }
  }

  void someMethod() { }
}

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.blocks

Parent Module

TreeWalker