com.puppycrawl.tools.checkstyle.checks.design

Class InterfaceIsTypeCheck

java.lang.Object

com.puppycrawl.tools.checkstyle.api.AutomaticBean

com.puppycrawl.tools.checkstyle.api.AbstractViolationReporter

com.puppycrawl.tools.checkstyle.api.AbstractCheck

com.puppycrawl.tools.checkstyle.checks.design.InterfaceIsTypeCheck

All Implemented Interfaces:

Configurable, Contextualizable

public final class InterfaceIsTypeCheck
extends AbstractCheck

Implements Joshua Bloch, Effective Java, Item 17 - Use Interfaces only to define types.

According to Bloch, an interface should describe a type. It is therefore inappropriate to define an interface that does not contain any methods but only constants. The Standard interface javax.swing.SwingConstants is an example of an interface that would be flagged by this check.

The check can be configured to also disallow marker interfaces like java.io.Serializable, that do not contain methods or constants at all.

• Property allowMarkerInterfaces - Control whether marker interfaces like Serializable are allowed. Type is boolean. Default value is true.

To configure the check:

 <module name="InterfaceIsType"/>
 

Example:

 public interface Test1 { // violation
     int a = 3;

 }

 public interface Test2 { // OK

 }

 public interface Test3 { // OK
     int a = 3;
     void test();
 }
 

To configure the check to report violation so that it doesn't allow Marker Interfaces:

 <module name="InterfaceIsType">
   <property name="allowMarkerInterfaces" value="false"/>
 </module>
 

Example:

 public interface Test1 { // violation
     int a = 3;
 }

 public interface Test2 { // violation

 }
 

Parent is com.puppycrawl.tools.checkstyle.TreeWalker

Violation Message Keys:

• interface.type

Since:

3.1

Nested Class Summary

Nested classes/interfaces inherited from class com.puppycrawl.tools.checkstyle.api.AutomaticBean

AutomaticBean.OutputStreamOptions

Field Summary

Fields

Modifier and Type	Field and Description
private boolean	allowMarkerInterfaces Control whether marker interfaces like Serializable are allowed.
static java.lang.String	MSG_KEY A key is pointing to the warning message text in "messages.properties" file.

Constructor Summary

Constructors

Constructor and Description
InterfaceIsTypeCheck()

Method Summary

Modifier and Type	Method and Description
int[]	getAcceptableTokens() The configurable token set.
int[]	getDefaultTokens() Returns the default token a check is interested in.
int[]	getRequiredTokens() The tokens that this check must be registered for.
void	setAllowMarkerInterfaces(boolean flag) Setter to control whether marker interfaces like Serializable are allowed.
void	visitToken(DetailAST ast) Called to process a token.

Methods inherited from class com.puppycrawl.tools.checkstyle.api.AbstractCheck

beginTree, clearViolations, destroy, finishTree, getFileContents, getLine, getLineCodePoints, getLines, getTabWidth, getTokenNames, getViolations, init, isCommentNodesRequired, leaveToken, log, log, log, setFileContents, setTabWidth, setTokens

Methods inherited from class com.puppycrawl.tools.checkstyle.api.AbstractViolationReporter

finishLocalSetup, getCustomMessages, getId, getMessageBundle, getSeverity, getSeverityLevel, setId, setSeverity

Methods inherited from class com.puppycrawl.tools.checkstyle.api.AutomaticBean

configure, contextualize, getConfiguration, setupChild

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

MSG_KEY

public static final java.lang.String MSG_KEY

A key is pointing to the warning message text in "messages.properties" file.

See Also:

Constant Field Values

allowMarkerInterfaces

private boolean allowMarkerInterfaces

Control whether marker interfaces like Serializable are allowed.

Constructor Detail

InterfaceIsTypeCheck

public InterfaceIsTypeCheck()

Method Detail

getDefaultTokens

public int[] getDefaultTokens()

Description copied from class: AbstractCheck

Returns the default token a check is interested in. Only used if the configuration for a check does not define the tokens.

Specified by:

getDefaultTokens in class AbstractCheck

Returns:

the default tokens

See Also:

TokenTypes

getRequiredTokens

public int[] getRequiredTokens()

Description copied from class: AbstractCheck

The tokens that this check must be registered for.

Specified by:

getRequiredTokens in class AbstractCheck

Returns:

the token set this must be registered for.

See Also:

TokenTypes

getAcceptableTokens

public int[] getAcceptableTokens()

Description copied from class: AbstractCheck

The configurable token set. Used to protect Checks against malicious users who specify an unacceptable token set in the configuration file. The default implementation returns the check's default tokens.

Specified by:

getAcceptableTokens in class AbstractCheck

Returns:

the token set this check is designed for.

See Also:

TokenTypes

visitToken

public void visitToken(DetailAST ast)

Description copied from class: AbstractCheck

Called to process a token.

Overrides:

visitToken in class AbstractCheck

Parameters:

ast - the token to process

setAllowMarkerInterfaces

public void setAllowMarkerInterfaces(boolean flag)

Setter to control whether marker interfaces like Serializable are allowed.

Parameters:

flag - whether to allow marker interfaces or not