Non-Serializable Comparator

ID

java.comparable_should_be_serializable

Severity

high

Remediation Complexity

trivial

Remediation Risk

low

Remediation Effort

low

Resource

Reliability

Language

Java

Tags

CWE:1066, reliability

Description

Reports a concrete class that implements Comparator without also implementing Serializable.

Rationale

Ordered collections such as TreeMap and TreeSet serialize their comparator along with their elements. If the comparator itself is not Serializable, the whole collection fails to serialize at runtime even though every element it holds is serializable.

// Bad - TreeSet built with this comparator cannot be serialized
public class ByPriority implements Comparator<Task> {
    public int compare(Task a, Task b) {
        return a.priority() - b.priority();
    }
}

Remediation

Add Serializable to the comparator’s implemented interfaces.

// Good
public class ByPriority implements Comparator<Task>, Serializable {
    private static final long serialVersionUID = 1L;

    public int compare(Task a, Task b) {
        return a.priority() - b.priority();
    }
}

References

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