EmptyCatchBlock

Since Checkstyle 6.4

Description

Checks for empty catch blocks. By default, check allows empty catch block with any comment inside.

Notes

There are two options to make validation more precise: exceptionVariableName and commentFormat. If both options are specified - they are applied by any of them is matching.

Properties

name description type default value since
commentFormat Specify the RegExp for the first comment inside empty catch block. If check meets comment inside empty catch block matching specified format - empty block is suppressed. If it is multi-line comment - only its first line is analyzed. Pattern ".*" 6.4
exceptionVariableName Specify the RegExp for the name of the variable associated with exception. If check meets variable name matching specified value - empty block is suppressed. Pattern "^$" 6.4

Examples

To configure the check: 

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

Such empty blocks would be both suppressed:

public class Example1 {
  private void exampleMethod1() {
    try {
      throw new RuntimeException();
    } catch (RuntimeException expected) {
    } // violation above
  }

  private void exampleMethod2() {
    try {
      throw new RuntimeException();
    } catch (RuntimeException ignore) {
      // no handling
    } // ok, catch block has comment
  }

  private void exampleMethod3 () {
    try {
      throw new RuntimeException();
    } catch (RuntimeException o) {
    } // violation above
  }

  private void exampleMethod4 () {
    try {
      throw new RuntimeException();
    } catch (RuntimeException ex) {
      // This is expected
    }
  }
}

To configure the check to suppress empty catch block if exception's variable name is expected or ignore or there's any comment inside: 

<module name="Checker">
  <module name="TreeWalker">
    <module name="EmptyCatchBlock">
      <property name="exceptionVariableName" value="expected|ignore"/>
    </module>
  </module>
</module>

Such empty blocks would be both suppressed:

public class Example2 {
  private void exampleMethod1() {
    try {
      throw new RuntimeException();
    } catch (RuntimeException expected) {
    }
  }

  private void exampleMethod2() {
    try {
      throw new RuntimeException();
    } catch (RuntimeException ignore) {
      // no handling
    }
  }

  private void exampleMethod3 () {
    try {
      throw new RuntimeException();
    } catch (RuntimeException o) {
    } // violation above
  }

  private void exampleMethod4 () {
    try {
      throw new RuntimeException();
    } catch (RuntimeException ex) {
      // This is expected
    }
  }
}

To configure the check to suppress empty catch block if single-line comment inside is "This is expected": 

<module name="Checker">
  <module name="TreeWalker">
    <module name="EmptyCatchBlock">
      <property name="commentFormat" value="This is expected"/>
    </module>
  </module>
</module>

Such empty blocks would be both suppressed:

public class Example3 {
  private void exampleMethod1() {
    try {
      throw new RuntimeException();
    } catch (RuntimeException expected) {
    } // violation above
  }

  private void exampleMethod2() {
    try {
      throw new RuntimeException();
    } catch (RuntimeException ignore) {
      // no handling
    } // violation 2 lines above
  }

  private void exampleMethod3 () {
    try {
      throw new RuntimeException();
    } catch (RuntimeException o) {
    } // violation above
  }

  private void exampleMethod4 () {
    try {
      throw new RuntimeException();
    } catch (RuntimeException ex) {
      // This is expected
    }
  }
}

To configure the check to suppress empty catch block if single-line comment inside is "This is expected": 

<module name="Checker">
  <module name="TreeWalker">
    <module name="EmptyCatchBlock">
      <property name="commentFormat" value="This is expected"/>
    </module>
  </module>
</module>

Such empty blocks would be both suppressed:

public class Example4 {
  private void exampleMethod1() {
    try {
      throw new RuntimeException();
    } catch (RuntimeException e) {
      //This is expected
    }
  }

  private void exampleMethod2() {
    try {
      throw new RuntimeException();
    } catch (RuntimeException e) {
      //   This is expected
    }
  }

  private void exampleMethod3 () {
    try {
      throw new RuntimeException();
    } catch (RuntimeException e) {
      // This is expected
      // some another comment
    }
  }

  private void exampleMethod4 () {
    try {
      throw new RuntimeException();
    } catch (RuntimeException e) {
      /* This is expected */
    }
  }

  private void exampleMethod5() {
    try {
      throw new RuntimeException();
      // violation below
    } catch (RuntimeException e) {
      /*
       *
       * This is expected
       * some another comment */
    }
  }
}

To configure the check to suppress empty catch block if exception's variable name is "myException": 

<module name="Checker">
  <module name="TreeWalker">
    <module name="EmptyCatchBlock">
      <property name="exceptionVariableName" value="myException"/>
    </module>
  </module>
</module>

Such empty blocks would be both suppressed:

public class Example5 {
  private void exampleMethod1() {
    try {
      throw new RuntimeException();
    } catch (RuntimeException e) {
    } // violation above
  }

  private void exampleMethod2() {
    try {
      throw new RuntimeException();
    } catch (RuntimeException myException) {
    }
  }
}

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