Unreachable catch clause¶
ID: java/unreachable-catch-clauseKind: problemSecurity severity: Severity: warningPrecision: highTags: - quality - reliability - correctness - exceptions - external/cwe/cwe-561Query suites: - java-security-and-quality.qls
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An unreachablecatch clause may indicate a logical mistake in the exception handling code or may simply be unnecessary.
Although certain unreachablecatch clauses cause a compiler error, there are also unreachablecatch clauses that do not cause a compiler error. Acatch clauseC is considered reachable by the compiler if both of the following conditions are true:
A checked exception that is thrown in the
tryblock is assignable to the parameter ofC.There is no previous
catchclause whose parameter type is equal to, or a supertype of, the parameter type ofC.However, acatchclause that is considered reachable by the compiler can be unreachable if both of the following conditions are true:The
catchclause’s parameter typeEdoes not include any unchecked exceptions.All exceptions that are thrown in the
tryblock whose type is a (strict) subtype ofEare already handled by previouscatchclauses.
Recommendation¶
Ensure that unreachablecatch clauses are removed or that further corrections are made to make them reachable.
Note that if atry-catch statement contains multiplecatch clauses, and an exception that is thrown in thetry block matches more than one of thecatch clauses, only the first matching clause is executed.
Example¶
In the following example, the secondcatch clause is unreachable. The code is incomplete because aFileOutputStream is opened but no methods are called to write to the stream. Such methods typically throwIOExceptions, which would make the secondcatch clause reachable.
FileOutputStreamfos=null;try{fos=newFileOutputStream(newFile("may_not_exist.txt"));}catch(FileNotFoundExceptione){// ask the user and try again}catch(IOExceptione){// more serious, abort}finally{if(fos!=null){try{fos.close();}catch(IOExceptione){/*ignore*/}}}
References¶
Java Language Specification:Execution of try-catch,Unreachable Statements.
Help - Eclipse Platform:Java Compiler Errors/Warnings Preferences.
Common Weakness Enumeration:CWE-561.