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 case or 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) {
      // ok, LITERAL_CATCH is not part of the tokens property.
    }
  }

  private void testBadSwitchStatement(int a) {
    switch (a) {
      case 1: { }

      case 2: {} {};

      case 3: {} { System.out.println(); }

      case 4: { System.out.println(); } {}
      default: { }
    }
  }

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

  private void testBadSwitchRule(int a) {
    switch (a) {
      case 1 -> { }
      default -> { }
    }
  }

  void someMethod() { }
}

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) {
      // ok, LITERAL_CATCH is not part of the tokens property.
    }
  }

  private void testBadSwitchStatement(int a) {
    switch (a) {
      case 1: { }

      case 2: {} {};

      case 3: {} { System.out.println(); }

      case 4: { System.out.println(); } {}
      default: { }
    }
  }

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

  private void testBadSwitchRule(int a) {
    switch (a) {
      case 1 -> { }
      default -> { }
    }
  }

  void someMethod() { }
}

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 emptyLoop() {
    for (int i = 0; i < 10; i++) {

    }

    try {
    }
    catch (Exception e) {
      // ok, LITERAL_CATCH is not part of the tokens property.
    }
  }

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

  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.

Fully Qualified Name

com.puppycrawl.tools.checkstyle.checks.blocks.EmptyBlockCheck

Use this fully qualified class name in configuration when an exact class reference is required.

Parent Module

TreeWalker