## com.puppycrawl.tools.checkstyle.checks.design
Class DesignForExtensionCheck

    java.lang.Object
      com.puppycrawl.tools.checkstyle.api.AutomaticBean
          com.puppycrawl.tools.checkstyle.api.AbstractViolationReporter
              com.puppycrawl.tools.checkstyle.api.Check
                  com.puppycrawl.tools.checkstyle.checks.design.DesignForExtensionCheck

All Implemented Interfaces:
  Configurable, Contextualizable

    public class DesignForExtensionCheck

extends Check

Checks that classes are designed for inheritance.

More specifically, it enforces a programming style where superclasses provide empty "hooks" that can be implemented by subclasses.

The exact rule is that nonprivate, nonstatic methods in nonfinal classes (or classes that do not only have private constructors) must either be

- abstract or
- final or
- have an empty implementation

This protects superclasses against beeing broken by subclasses. The downside is that subclasses are limited in their flexibility, in particular they cannot prevent execution of code in the superclass, but that also means that subclasses can't forget to call their super method.

Author:
  lkuehne

Constructor Summary
`DesignForExtensionCheck()`

Method Summary
`int[]` `getDefaultTokens()` Returns the default token a check is interested in.
`void` `visitToken(DetailAST aAST)` Called to process a token.

Methods inherited from class com.puppycrawl.tools.checkstyle.api.Check
`beginTree, destroy, finishTree, getAcceptableTokens, getClassLoader, getFileContents, getLines, getRequiredTokens, getTabWidth, getTokenNames, init, leaveToken, log, log, setClassLoader, setFileContents, setMessages, setTabWidth, setTokens`

Methods inherited from class com.puppycrawl.tools.checkstyle.api.AbstractViolationReporter
`getCustomMessages, getId, getMessageBundle, getSeverity, getSeverityLevel, log, setId, setSeverity`

Methods inherited from class com.puppycrawl.tools.checkstyle.api.AutomaticBean
`configure, contextualize, finishLocalSetup, getConfiguration, setupChild`

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Constructor Detail

### DesignForExtensionCheck

    public DesignForExtensionCheck()

Method Detail

### getDefaultTokens

    public int[] getDefaultTokens()

  Description copied from class: `Check`
  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 `Check`
  Returns:
    the default tokens
  See Also:
    `TokenTypes`

### visitToken

    public void visitToken(DetailAST aAST)

  Description copied from class: `Check`
  Called to process a token.

  Overrides:
    `visitToken` in class `Check`
  Parameters:
    `aAST` - the token to process

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