rspec/rules/S3676/java/rule.adoc

== Why is this an issue?

The ``++Class.isInstance++`` method is the dynamic equivalent of the ``++instanceof++`` operator. According to the JavaDoc, ``++isInstance++``


____
returns ``++true++`` if the specified Object argument is an instance of the represented class (or of any of its subclasses); it returns ``++false++`` otherwise

____ 


Thus, calling ``++isInstance++`` with a class argument is likely a mistake, since any random ``++Class++`` will only be "an instance of the represented class" when the left-hand side of the call is ``++Class.class++`` itself. To test for a class/sub-class relationship, use ``++isAssignableFrom++`` instead.


=== Noncompliant code example

[source,java]
----
    Class<Number> num = Number.class;
    Class<BigInteger> bi = BigInteger.class;

    System.out.println(num.isInstance(bi));  // Noncompliant. false
    System.out.println(bi.isInstance(Class.class));  // Noncompliant. false
    System.out.println(Class.class.isInstance(bi));  // Noncompliant. true
----


=== Compliant solution

[source,java]
----
    Class<Number> num = Number.class;
    Class<BigInteger> bi = BigInteger.class;

    System.out.println(num.isAssignableFrom(bi));  // true
    System.out.println(bi.isAssignableFrom(Class.class));  // false
    System.out.println(Class.class.isAssignableFrom(bi));  // false
----


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