64 lines
1.6 KiB
Plaintext
64 lines
1.6 KiB
Plaintext
== Why is this an issue?
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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 https://docs.oracle.com/javase/8/docs/api/java/lang/Class.html#isInstance-java.lang.Object-[isInstance()] from ``++java.lang.Class++`` works differently and does type check at runtime only, incompatible types will therefore not be detected early in the development, potentially resulting in dead code. The ``++isInstance()++`` method should only be used in dynamic cases when the ``++instanceof++`` operator can't be used.
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This rule raises an issue when ``++isInstance()++`` is used and could be replaced with an ``++instanceof++`` check.
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=== Noncompliant code example
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[source,java]
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----
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int f(Object o) {
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if (String.class.isInstance(o)) { // Noncompliant
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return 42;
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}
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return 0;
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}
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int f(Number n) {
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if (String.class.isInstance(n)) { // Noncompliant
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return 42;
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}
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return 0;
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}
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----
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=== Compliant solution
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[source,java]
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----
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int f(Object o) {
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if (o instanceof String) { // Compliant
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return 42;
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}
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return 0;
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}
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int f(Number n) {
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if (n instanceof String) { // Compile-time error
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return 42;
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}
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return 0;
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}
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boolean fun(Object o, String c) throws ClassNotFoundException
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{
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return Class.forName(c).isInstance(o); // Compliant, can't use instanceof operator here
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}
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----
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ifdef::env-github,rspecator-view[]
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'''
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== Implementation Specification
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(visible only on this page)
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include::message.adoc[]
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include::highlighting.adoc[]
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endif::env-github,rspecator-view[]
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