Is there a tool for reporting downcasts in Java?

Question

Wondering if there is a reporting tool (such as PMD) which reports downcasting in Java code.

Answer 1

Catching all casts is easy with a custom PMD rule:

import net.sourceforge.pmd.AbstractJavaRule;
import net.sourceforge.pmd.ast.ASTCastExpression;

public class CastRule extends AbstractJavaRule {

    public CastRule() {
    }

    @Override
    public Object visit(final ASTCastExpression node, final Object data) {
        addViolation(data, node);
        return super.visit(node, data);
    }
}

Unfortunately it catches upcasts too if they are explicit upcasts. Some example:

final Number myNumber = 5;
final Integer myInteger = (Integer) myNumber; // catched

final Number myNumber2 = (Number) myInteger; // catched
final Number myNumber3 = myInteger; // NOT catched

Catching only downcasts looks rather complicated with PMD.

Check this answer too, it contains some details about the usage.