Block Checks Checkstyle Development Team

Checks for empty blocks.

name description type default value
option policy on block contents block policy stmt
tokens blocks to check subset of tokens LITERAL_DO, LITERAL_ELSE, LITERAL_FINALLY, LITERAL_IF, LITERAL_FOR, LITERAL_TRY, LITERAL_WHILE, INSTANCE_INIT, STATIC_INIT, LITERAL_SWITCH. all tokens

To configure the check:

<module name="EmptyBlock"/>

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

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

com.puppycrawl.tools.checkstyle.checks.blocks

TreeWalker

Checks for empty catch blocks. There are two options to make validation more precise (by default Check allows empty catch block with any comment inside):

name description type default value
exceptionVariableName The name of variable associated with exception String ^$
commentFormat The format of the first comment inside empty catch String .*

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

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

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

To configure the Check to suppress empty catch block if single-line comment inside is "//This is expected" or exception's variable name is "myException" (any option is matching):

<module name="EmptyCatchBlock"> <property name="commentFormat" value="This is expected"/> <property name="exceptionVariableName" value="myException"/> </module>

Such empty blocks would be suppressed:

try { throw new RuntimeException(); } catch (RuntimeException e) { //This is expected } ... try { throw new RuntimeException(); } catch (RuntimeException e) { // This is expected } ... try { throw new RuntimeException(); } catch (RuntimeException e) { // This is expected // some another comment } ... try { throw new RuntimeException(); } catch (RuntimeException e) { /* This is expected */ } ... try { throw new RuntimeException(); } catch (RuntimeException e) { /* * * This is expected * some another comment */ } ... try { throw new RuntimeException(); } catch (RuntimeException myException) { }

com.puppycrawl.tools.checkstyle.checks.blocks

TreeWalker

Checks for the placement of left curly braces ('{') for code blocks. The policy to verify is specified using the property option. Policies eol and nlow take into account the property maxLineLength.

name description type default value
option policy on placement of a left curly brace ('{') left curly brace policy eol
ignoreEnums If true, Check will ignore enums boolean true
maxLineLength maximum number of characters in a line integer 80
tokens blocks to check subset of tokens ANNOTATION_DEF, CLASS_DEF, CTOR_DEF, ENUM_DEF, ENUM_CONSTANT_DEF, INTERFACE_DEF, LITERAL_CATCH, LITERAL_DO, LITERAL_ELSE, LITERAL_FINALLY, LITERAL_FOR, LITERAL_IF, LITERAL_SWITCH, LITERAL_SYNCHRONIZED, LITERAL_TRY, LITERAL_WHILE, METHOD_DEF all tokens

To configure the check:

<module name="LeftCurly"/>

To configure the check to apply the nl policy to type blocks:

<module name="LeftCurly"> <property name="option" value="nl"/> <property name="tokens" value="CLASS_DEF,INTERFACE_DEF"/> </module>

An example of how to configure the check to validate enum definitions:

<module name="LeftCurly"> <property name="ignoreEnums" value="false"/> </module>

com.puppycrawl.tools.checkstyle.checks.blocks

TreeWalker

Checks for braces around code blocks.

name description type default value
tokens blocks to check subset of tokens LITERAL_DO, LITERAL_ELSE, LITERAL_IF, LITERAL_FOR, LITERAL_WHILE all tokens
allowSingleLineStatement allows single-line statements without braces boolean false

To configure the check:

<module name="NeedBraces"/>

To configure the check for if and else blocks:

<module name="NeedBraces"> <property name="tokens" value="LITERAL_IF, LITERAL_ELSE"/> </module>

To configure the check to allow single-line statements (if, while, do-while, for) without braces:

<module name="NeedBraces"> <property name="allowSingleLineStatement" value="true"/> </module>

Next statements won't be violated by Check:

if (obj.isValid()) return true; // OK while (obj.isValid()) return true; // OK do this.notify(); while (o != null); // OK for (int i = 0; ; ) this.notify(); // OK

To configure the Check to allow case, default single-line statements without braces:

<module name="NeedBraces"> <property name="tokens" value="LITERAL_CASE, LITERAL_DEFAULT"/> <property name="allowSingleLineStatement" value="true"/> </module>

Next statements won't be violated by Check:

switch (num) { case 1: counter++; break; // OK case 6: counter += 10; break; // OK default: counter = 100; break; // OK }

com.puppycrawl.tools.checkstyle.checks.blocks

TreeWalker

Checks the placement of right curly braces ('}') for else, try, and catch tokens. The policy to verify is specified using the property option.

name description type default value
option policy on placement of a right curly brace ('}') right curly brace policy same
tokens blocks to check subset of tokens LITERAL_TRY, LITERAL_CATCH, LITERAL_FINALLY, LITERAL_IF, LITERAL_ELSE, CLASS_DEF, METHOD_DEF, CTOR_DEF, LITERAL_FOR, LITERAL_WHILE, LITERAL_DO, STATIC_INIT, INSTANCE_INIT. LITERAL_TRY, LITERAL_CATCH, LITERAL_FINALLY, LITERAL_IF, LITERAL_ELSE
shouldStartLine should we check if '}' starts line. boolean true

To configure the check:

<module name="RightCurly"/>

To configure the check with policy alone for else and METHOD_DEF tokens:

<module name="RightCurly"> <property name="option" value="alone"/> <property name="tokens" value="LITERAL_ELSE, METHOD_DEF"/> </module>

com.puppycrawl.tools.checkstyle.checks.blocks

TreeWalker

Finds nested blocks, i.e. blocks that are used freely in the code.

Rationale: Nested blocks are often leftovers from the debugging process, they confuse the reader.

For example this Check finds the obsolete braces in

public void guessTheOutput() { int whichIsWhich = 0; { int whichIsWhich = 2; } System.out.println("value = " + whichIsWhich); }

and debugging / refactoring leftovers such as

// if (conditionThatIsNotUsedAnyLonger) { System.out.println("unconditional"); }

A case in a switch statement does not implicitly form a block. Thus to be able to introduce local variables that have case scope it is necessary to open a nested block. This is supported, set the allowInSwitchCase property to true and include all statements of the case in the block.

switch (a) { case 0: // Never OK, break outside block { x = 1; } break; case 1: // Never OK, statement outside block System.out.println("Hello"); { x = 2; break; } case 1: // OK if allowInSwitchCase is true { System.out.println("Hello"); x = 2; break; } }
name description type default value
allowInSwitchCase Allow nested blocks in case statements boolean false

To configure the check:

<module name="AvoidNestedBlocks"/>

com.puppycrawl.tools.checkstyle.checks.blocks

TreeWalker