[java] UnnecessaryCast Reported But Cast Is Needed.

May 14, 2025 by ADMIN 52 views

Introduction

In this article, we will discuss a known issue with the UnnecessaryCast rule in PMD version 7.13.0. This rule is designed to detect unnecessary casts in Java code, but it can sometimes report false positives. We will explore a specific scenario where the rule falsely marks a cast as unnecessary when a method in another class is used.

Affects PMD Version

The issue we are about to discuss affects PMD version 7.13.0. It is essential to note that this problem may be resolved in later versions of PMD.

Rule

The UnnecessaryCast rule is a part of the PMD ruleset for Java codestyle. It can be found in the PMD documentation at the following link:

https://docs.pmd-code.org/latest/pmd_rules_java_codestyle.html#unnecessarycast

Description

The UnnecessaryCast rule is designed to detect unnecessary casts in Java code. However, in certain situations, it can report false positives. One such scenario is when a method in another class is used. The rule works correctly if the cast is applied to the method's actual result but fails if it is done at the row's end result.

Code Sample Demonstrating the Issue

The following code sample demonstrates the issue:

public class CastProblem {

	static double getDouble() {
		return 1.0;
	}

	public static void main(String[] args) {

		// Local method - OK
		int result = (int) getDouble() * 100;
		result += (int) (getDouble() * 100);

		// Inner class - OK
		OtherInnerClass otherInnerClass = new OtherInnerClass();
		result += (int) otherInnerClass.getDouble() * 100;
		result += (int) (otherInnerClass.getDouble() * 100);

		// External class - reports unnecessary cast
		OtherClass otherClass = new OtherClass();
		// OK when casting the first argument
		result += (int) otherClass.getDouble() * 100;

		// Reports Unnecessary cast when casting the whole expression
		// This is not correct. Removing the cast cause a compilation error
		result += (int) (otherClass.getDouble() * 100);

		// Just a bogus line to get rid of unused variable warning
		System.exit(result > 1 ? 1 : 0);
	}

	private static class OtherInnerClass {

		public double getDouble() {
			return 1.0;
		}
	}
}

public class OtherClass {
	public double getDouble() {
		return 1.0;
	}
}

Expected Outcome

PMD reports a violation at line: result += (int) (otherClass.getDouble() * 100);, but that's wrong. That's a false positive.

Running PMD through Gradle

To reproduce the issue, you can run PMD through Gradle. The following command will run PMD on the CastProblem class:

./gradlew pmdMain

This will generate a report that includes the false positive reported by the UnnecessaryCast rule.

Conclusion

In this article, we discussed a known issue with the UnnecessaryCast rule in PMD version 7.13.0. The rule can report false positives when a method in another class is used. We provided a code sample that demonstrates the issue and explained how to reproduce it using Gradle. This problem may be resolved in later versions of PMD.

Workaround

One possible workaround for this issue is to disable the UnnecessaryCast rule or to use a different rule that is less prone to false positives. However, this may not be a viable solution in all cases, especially if the rule is essential for your project's coding standards.

Future Development

The developers of PMD are aware of this issue and may address it in future versions of the tool. In the meantime, users can work around the problem by using the workaround mentioned above or by reporting the issue to the PMD developers.

Related Issues

This issue is related to other PMD rules that deal with casts and type conversions. Users who experience similar issues with other rules may want to investigate these related issues to see if they can find a solution that works for their project.

Additional Resources

For more information on PMD and its rules, please refer to the PMD documentation:

https://docs.pmd-code.org/latest/pmd_rules_java_codestyle.html

Additionally, users can search for related issues on the PMD issue tracker:

https://github.com/pmd/pmd/issues

By understanding this issue and its implications, developers can write better code and avoid unnecessary casts that can lead to errors and bugs.

Introduction

In our previous article, we discussed a known issue with the UnnecessaryCast rule in PMD version 7.13.0. This rule is designed to detect unnecessary casts in Java code, but it can sometimes report false positives. In this article, we will provide a Q&A section to help developers understand the issue and its implications.

Q: What is the UnnecessaryCast rule in PMD?

A: The UnnecessaryCast rule is a part of the PMD ruleset for Java codestyle. It is designed to detect unnecessary casts in Java code.

Q: What is the issue with the UnnecessaryCast rule?

A: The issue with the UnnecessaryCast rule is that it can report false positives when a method in another class is used. The rule works correctly if the cast is applied to the method's actual result but fails if it is done at the row's end result.

Q: What is the code sample that demonstrates the issue?

A: The code sample that demonstrates the issue is provided in our previous article. It includes a class called CastProblem that has a method called getDouble() that returns a double value. The method is used in different ways to demonstrate the issue.

Q: How can I reproduce the issue?

A: To reproduce the issue, you can run PMD through Gradle on the CastProblem class. The following command will generate a report that includes the false positive reported by the UnnecessaryCast rule:

./gradlew pmdMain

Q: What is the expected outcome?

A: The expected outcome is that PMD reports a violation at line: result += (int) (otherClass.getDouble() * 100);, but that's wrong. That's a false positive.

Q: What is the workaround for this issue?

A: One possible workaround for this issue is to disable the UnnecessaryCast rule or to use a different rule that is less prone to false positives. However, this may not be a viable solution in all cases, especially if the rule is essential for your project's coding standards.

Q: Will this issue be fixed in future versions of PMD?

A: The developers of PMD are aware of this issue and may address it in future versions of the tool. In the meantime, users can work around the problem by using the workaround mentioned above or by reporting the issue to the PMD developers.

Q: Are there any related issues with other PMD rules?

A: Yes, this issue is related to other PMD rules that deal with casts and type conversions. Users who experience similar issues with other rules may want to investigate these related issues to see if they can find a solution that works for their project.

Q: Where can I find more information on PMD and its rules?

A: For more information on PMD and its rules, please refer to the PMD documentation:

https://docs.pmd-code.org/latest/pmd_rules_java_codestyle.html

Additionally, users can search for related issues on the PMD issue tracker:

https://github.com/pmd/pmd/issues

Q: How can I report this issue to the PMD developers?

A: To report this issue to the PMD developers, you can create a new issue on the PMD issue trackerhttps://github.com/pmd/pmd/issues/new

Please provide as much detail as possible, including the code sample that demonstrates the issue and the expected outcome.

Conclusion

In this Q&A article, we provided answers to common questions about the UnnecessaryCast rule in PMD and its known issue. We hope that this information will help developers understand the issue and its implications and find a solution that works for their project.