Java generics work one time, does not compile second time -


this accessor method collection in class abstractnode:

public list<polygonalchain> getoutedges() {     return collections.unmodifiablelist(outedges); }

but following not work, compilation error message is: incompatible types: java.lang.object cannot converted .....formulaelements.polygonalchain

abstractnode anodeexample = getconnectingshape(); for(polygonalchain outedge: anodeexample.getoutedges()){     //do stuff }

what more confusing me, can use following code in descendants of abstractnode without error:

for(polygonalchain outedge: getoutedges()){     outedge.delete(); }

here minimal code, causes problem:

package brokengenerics;  import java.math.biginteger; import java.util.list;   public class brokengenerics { public static abstract class aclass <e extends number> {     private list<b> bs;      public list<b> getbs(){         return bs;     }  } public static class b extends aclass<biginteger>{  }  public static aclass getsomething(){     return new b(); } /**  * @param args command line arguments  */ public static void main(string[] args) {      for(b desc : getsomething().getbs())){  } }  }


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