Adobe-Consulting-Services/acs-aem-commons

        return ParameterizedType.class.isInstance(type);

Close

The instanceof construction is a preferred way to check whether a variable can be cast to some type statically because a compile-time error will occur in case of incompatible types. The method isInstance() from java.lang.Class works differently and does type check at runtime only, incompatible types will therefore not be detected early in the developement, potentially resulting in dead code. The isInstance() method should only be used in dynamic cases when the instanceof operator can't be used.

This rule raises an issue when isInstance() is used and could be replaced with an instanceof check.

Noncompliant Code Example

int f(Object o) {
  if (String.class.isInstance(o)) {  // Noncompliant
    return 42;
  }
  return 0;
}

int f(Number n) {
  if (String.class.isInstance(n)) {  // Noncompliant
    return 42;
  }
  return 0;
}

Compliant Solution

int f(Object o) {
  if (o instanceof String) {  // Compliant
    return 42;
  }
  return 0;
}

int f(Number n) {
  if (n instanceof String) {  // Compile-time error
    return 42;
  }
  return 0;
}

boolean fun(Object o, String c) throws ClassNotFoundException
{
  return Class.forName(c).isInstance(o); // Compliant, can't use instanceof operator here
}

    public static <T> T[] toArray(Collection<T> c, Class klass) {

Close

Generic types shouldn't be used raw (without type parameters) in variable declarations or return values. Doing so bypasses generic type checking, and defers the catch of unsafe code to runtime.

Noncompliant Code Example

List myList; // Noncompliant
Set mySet; // Noncompliant

Compliant Solution

List<String> myList;
Set<? extends Number> mySet;

 * ACS AEM Commons

Close

Checks the header of a source file against a header that contains aregular expression for each line of the source header.

Rationale: In some projects checking against afixed header is not sufficient, e.g. the header might require acopyright line where the year information is not static.

For example, consider the following header:

<source><br>line 1: ^/{71}$<br>line 2: ^// checkstyle:$<br>line 3: ^// Checks Java source code for adherence to a set of rules\.$<br>line 4: ^// Copyright \(C\) \d\d\d\d Oliver Burn$<br>line 5: ^// Last modification by \$Author.*\$$<br>line 6: ^/{71}$<br>line 7:<br>line 8: ^package<br>line 9:<br>line 10: ^import<br>line 11:<br>line 12: ^/\*\*<br>line 13: ^ \*([^/]|$)<br>line 14: ^ \*/<br> </source>

Lines 1 and 6 demonstrate a more compact notation for 71 '/'characters. Line 4 enforces that the copyright notice includes afour digit year. Line 5 is an example how to enforce revisioncontrol keywords in a file header. Lines 12-14 is a template forjavadoc (line 13 is so complicated to remove conflict with and ofjavadoc comment). Lines 7, 9 and 11 will be treated as '^$' andwill forcefully expect the line to be empty.

Different programming languages have different comment syntaxrules, but all of them start a comment with a non-wordcharacter. Hence you can often use the non-word characterclass to abstract away the concrete comment syntax and allowchecking the header for different languages with a singleheader definition. For example, consider the following headerspecification (note that this is not the full Apache licenseheader):

<source><br>line 1: ^#!<br>line 2: ^&lt;\?xml.*&gt;$<br>line 3: ^\W*$<br>line 4: ^\W*Copyright 2006 The Apache Software Foundation or its licensors, as applicable\.$<br>line 5: ^\W*Licensed under the Apache License, Version 2\.0 \(the "License"\);$<br>line 6: ^\W*$<br> </source>

Lines 1 and 2 leave room for technical header lines, e.g. the"#!/bin/sh" line in Unix shell scripts, or the XML file headerof XML files. Set the multiline property to "1, 2" so theselines can be ignored for file types where they do no apply.Lines 3 through 6 define the actual header content. Note howlines 2, 4 and 5 use escapes for characters that have specialregexp semantics.

In default configuration, if header is not specified, the default valueof header is set to null and the check does not rise any violations.

This documentation is written and maintained by the Checkstyle community and is covered under the same license as the Checkstyle project.