Analysis Details

For parameter types, favor interfaces over classes

es.uniovi.reflection.analyses.bloch.7.40.2

This rule detects parameters whose type implements an interface that can be safely used to type the parameter instead. This means that all the methods invoked by and attributes accessed on the parameter must belong to the interface type (or the Object class). If the parameter is passed as argument to some method, this method must accept the interface type as argument too. If the parameter is iterated in a for-each loop, the interface type must extend the java.lang.Iterable interface. Additionally, if the parameter is assigned to some variable, it will be checked that the type of this variable canbe safely changed to the interface type too. Also, if the parameter belongs to a method that overrides or is overridden by another method, it will not be considered. Parameters whose type is an enum or already an interface are not considered. Finally, too general interfaces such as java.io.Serializable, java.lang.Comparable, java.lang.Cloneable, java.lang.constant.Constable, java.lang.constant.ConstantDesc and java.lang.CharSequence are not recommended for the change.

Computational Reflection Research Group

09-30-2026 22:23

Bad Practice

Parameter Declaration

MATCH (enclosingCU:ORDINARY_CU)-[:DECLARES_TYPE| HAS_NESTED_TYPE]-> (typeDec:TYPE_DEC{accessLevel:'public'})-[:DECLARES_METHOD | DECLARES_CONSTRUCTOR]->(callable:CALLABLE_DEC{accessLevel:'public', isUserCode:TRUE})-[:CALLABLE_PARAM]->(param)-[:ITS_TYPE_IS]->(paramType)-[:EXTENDS_CLASS | IMPLEMENTS_INTERFACE | PARAMETERIZES_TYPE*]->(candidateInterface:INTERFACE_DEC), (param)-[:USED_BY | MODIFIED_BY | STATE_MODIFIED_BY]->()
WHERE NOT EXISTS((paramType)-[:PARAMETERIZES_TYPE]->(:INTERFACE_DEC)) AND NOT callable.isAbstract AND NOT paramType:INTERFACE_DEC AND NOT paramType:ENUM_DEC AND NOT EXISTS(()-[:OVERRIDES]-(callable)) AND NOT EXISTS((param)-[:USED_BY]->()<-[:IDENT_SELECTION_FROM]-(:METHOD_SELECTION{selectedName:'clone'})) AND NOT candidateInterface.fullyQualifiedName IN ['java.io.Serializable','java.lang.Comparable', 'java.lang.Cloneable', 'java.lang.constant.Constable', 'java.lang.constant.ConstantDesc', 'java.lang.CharSequence']
CALL apoc.path.subgraphNodes(param, {filterStartNode:TRUE, minLevel:0, labelFilter:'>VARIABLE_DEC', relationshipFilter:'>USED_BY|<ASSIGNMENT_RHS|<INITIALIZATION_EXPR|<VAR_DEC_INIT|<MODIFIED_BY'}) YIELD node as alias
OPTIONAL MATCH (alias)-[:USED_BY]->()<-[:IDENT_SELECTION_FROM]-(:METHOD_SELECTION)<-[:INVOCATION_METHOD_SELECTION]-( )-[:CALLEE]->(selectedMethodDec)
OPTIONAL MATCH (selectedMethodDec)-[:OVERRIDES*0..]->()<-[invocationCoveredByI:DECLARES_METHOD]-( )<-[:IMPLEMENTS_INTERFACE|PARAMETERIZES_TYPE*0..]-(candidateInterface)
OPTIONAL MATCH (selectedMethodDec)-[:OVERRIDES*0..]->()<-[invocationCoveredByO:DECLARES_METHOD]-(:CLASS_DEC{fullyQualifiedName:'java.lang.Object'})
WITH DISTINCT enclosingCU, typeDec, callable, param, alias, candidateInterface, selectedMethodDec IS NULL OR invocationCoveredByI IS NOT NULL OR invocationCoveredByO IS NOT NULL AS invocationCovered
OPTIONAL MATCH (alias)-[:USED_BY]->()<- [:FOREACH_EXPR]-(foreach)
OPTIONAL MATCH (candidateInterface)-[coveredForEach:IMPLEMENTS_INTERFACE|PARAMETERIZES_TYPE*0..]->({fullyQualifiedName:'java.lang.Iterable'})
WITH DISTINCT enclosingCU, typeDec, callable, param, alias, candidateInterface, invocationCovered, foreach IS NULL OR coveredForEach IS NOT NULL as foreachCovered
OPTIONAL MATCH (alias)-[:USED_BY]->()<- [argRel:INVOCATION_ARG | NEW_INSTANCE_ARG]-( :CALL)-[:CALLEE]->()-[:ITS_TYPE_IS]->()-[paramRel:PARAM_TYPE]->(argParamType) WHERE argRel.argumentIndex=paramRel.paramIndex
OPTIONAL MATCH (candidateInterface)-[coveredArg:IMPLEMENTS_INTERFACE|PARAMETERIZES_TYPE*0..]->(argParamType)
WITH DISTINCT enclosingCU, typeDec, callable, param, alias, candidateInterface, invocationCovered, foreachCovered, EXISTS((alias)-[:USED_BY]->()<-[:RETURN_EXPR]-()) as usedInReturn, argRel IS NULL OR coveredArg IS NOT NULL OR argParamType.fullyQualifiedName='java.lang.Object' AS argCovered
OPTIONAL MATCH (alias)-[:USED_BY]->()<-[:IDENT_SELECTION_FROM]-(attrSelection:FIELD_SELECTION)
OPTIONAL MATCH (candidateInterface)-[:IMPLEMENTS_INTERFACE|PARAMETERIZES_TYPE*0..]->()-[:DECLARES_FIELD]->(coveredField{name:attrSelection.selectedName, actualType:attrSelection.actualType})
WITH DISTINCT enclosingCU, typeDec, callable, param, candidateInterface, NOT ANY(usedInRet IN COLLECT(usedInReturn) WHERE usedInRet) AND ALL(invCovered in COLLECT(invocationCovered) WHERE invCovered) AND ALL(foreachCov in COLLECT(foreachCovered) WHERE foreachCov) AND ALL(argCov in COLLECT(argCovered) WHERE argCov) AND ALL(attrCov in COLLECT(attrSelection IS NULL OR coveredField IS NOT NULL) WHERE attrCov) AS paramCovered
WHERE paramCovered
WITH enclosingCU, typeDec, callable, param, apoc.text.join(COLLECT(candidateInterface.fullyQualifiedName), ',') AS candidateInts
RETURN '{"node":"PARAMETER '+param.actualType+' '+param.name+'","line":"'+param.lineNumber+'","column":"'+param.column+'","rule":"BLOCH-7.40.2","location":"'+enclosingCU.fileName+'","message":"Parameter ' + param.name + ' at line ' + param.lineNumber + ' in callable ' + callable.fullyQualifiedName + ' is declared as type ' + param.actualType + '. However, it should be declared as type(s) ' + candidateInts + ' to favor the use of interfaces in public methods."}'