44 lines
1.6 KiB
Plaintext
44 lines
1.6 KiB
Plaintext
== Why is this an issue?
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The Java Collections framework defines interfaces such as `java.util.List` or `java.util.Map`. Several implementation classes are provided for each of those interfaces to fill different needs: some of the implementations guarantee a few given performance characteristics, some others ensure a given behavior, for example immutability.
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Among the methods defined by the interfaces of the Collections framework, some are declared as "optional": an implementation class may choose to throw an `UnsupportedOperationException` when one of those methods is called. For example, `java.util.Collections.emptyList()` returns an implementation of `java.util.List` which is documented as "immutable": calling the `add` method on this object triggers an `UnsupportedOperationException`.
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When calling one of the "optional" methods, a developer should therefore make sure that the implementation class on which the call is made indeed supports this method.
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=== Noncompliant code example
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[source,java]
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----
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List<String> list = Collections.emptyList();
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if (someCondition) {
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list.add("hello"); // Noncompliant; throws an UnsupportedOperationException
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}
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return list;
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----
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=== Compliant solution
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[source,java]
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----
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List<String> list = new ArrayList<>();
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if (someCondition) {
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list.add("hello");
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}
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return list;
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----
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or
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[source,java]
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----
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if (someCondition) {
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return Collections.singletonList("hello");
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}
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return Collections.emptyList();
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----
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== Resources
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* https://docs.oracle.com/javase/8/docs/technotes/guides/collections/overview.html[Collections Framework Overview] in the Java documentation
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