java - What is the correct way to compare two throwables? -

i using junit rule re-run failed tests. requirement is, if re-run fails, determine whether failed same reason.

to i've adapted code this answer keep record of failures , compare them. however, comparison (.equals) evaluates false despite them failing same reason. best way go this?

  private statement statement(final statement base, final description description) {     return new statement() {       @override       public void evaluate() throws throwable {          (int = 0; < retrycount; i++) {           try {             base.evaluate();             return;           } catch (throwable t) {             system.err.println(description.getdisplayname() + ": run " + (i + 1) + " failed");              // compare error 1 before it.             if (errors.size() > 0) {               if (t.equals(errors.get(errors.size() - 1))) {                 system.out.println("the error same previous one!");               } else {                 system.out.println("the error different previous one.");               }             }              errors.add(t);           }         }         system.err.println(description.getdisplayname() + ": giving after " + retrycount             + " failures");          // throw recent error.         throw errors.get(errors.size() - 1);       }     };   } 

equality throwable defined "the same throwable". (it compares references.)

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"same reason" need think , define application.

one way define "the same type , loosely same throw statement":

static boolean sametypeandline(throwable t1, throwable t2) {     if (t1.getclass() == t2.getclass()) {         stacktraceelement[] trace1 = t1.getstacktrace();         stacktraceelement[] trace2 = t2.getstacktrace();         return trace1[0].equals(trace2[0]);     } else {         return false;     } } 

but still has ambiguity:

• if (bad1 || bad2) {     // same throw site, different conditions     throw new exception(...); } 

• // throws nullpointerexeption // (was foo or result of bar() null?) object baz = foo.bar().baz(); 

so, best thing can define reasons exceptions:

class myexception {     final reason reason;      myexception(reason reason) {         this.reason = reason;     }      // or class, or whatever need     enum reason {a, b, c} } 

and check against those. additionally, use coding style prevents ambiguities.