java.lang.ClassCastException: cannot be cast to java.lang.Integer -

i wanted create compareto method gives me error. can me ?

     package defaultpackage;      public class huffmanentry implements entry<integer, string> {      private string c;        private integer freq;       public huffmanentry(string c, integer freq){          this.c = c;      this.freq = freq;      }       @override      public int compareto(integer arg0) {     if(getkey()<arg0){         return -1;     }else if(getkey()>arg0){         return 1;     }else{         return 0;        } }        @override       public integer getkey() {       return freq;       } 

here's error:

exception in thread "main" java.lang.classcastexception: defaultpackage.huffmanentry cannot cast java.lang.integer @ defaultpackage.huffmanentry.compareto(huffmanentry.java:1) 

there serious problems quality of "evidence" have provided us:

1. the stacktrace seems exception thrown @ line 1 of huffmanentry.java, , impossible.

2. the stacktrace seems code attempting cast huffmanentry object integer in compareto, (according source code) cannot happen in method. objects used in method have declared type of integer, , there no explicity typecasts.

3. the stacktrace shows compareto 1 , method call, , impossible.

^{(3 impossible things before lunch? nah! don't buy it!)}

in short, evidence have shown not real. has been tweaked / mangled, , in ways make impossible interpret.

please provide real (complete , unedited) stacktrace, , source code precisely matches compiled code ran produce stacktrace. compilation errors.

alternatively, provide sscce can run ourselves reproduce facially impossible behaviour / evidence.

---

looking @ code linked to, think understand general problem ... if not specific one.

basically, mixing generic , non-generic code , (you must be) ignoring resulting compiler warnings unchecked conversions, use of raw types , on. result errors should picked java compile-time type checker not being reported.

for example, in myheap.java, write:

private arraylist<entry> entrylist;  

but entry generic interface, meaning arraylist being interpreted arraylist<entry<object, object>> object raw type corresponding unbounded type parameters k , t. there int compareto(k) method in entry interface ... , raw type signature int compareto(object).

now @

if (entrylist.get(i*2).compareto(entrylist.get(i*2+1))==-1){  

note calling entry.compareto(object) passing entry argument. compiler has said ok .... because thinks using raw types @ point. if had been using generics properly, compiler have realized calling entry<k, v>.compareto(entry<k, v>) generic method signature entry<k, v>.compareto(v) . have been flagged compilation error.

i suspect explains strange exception too. java compiler has added hidden runtime typecasts make sure jvm's core runtime type safety not compromised. seeing exception when 1 of runtime checks fails. , happens because ignored or suppressed compile time checks should have told of programming error.

anyway, bottom line should not ignore compiler warnings misuse of generics, unchecked conversions, etc. @ peril ... , in case, got bitten.