java - How do I subclass ArrayList, and require that <E> must extend Comparable -

i think i'm trying clear, i'm no generics expert.

import java.util.arraylist; public class minheap<e extends comparable> extends arraylist<e>  {     /* simple wrapper around list make binary min-heap. */     public minheap() {         super();     }      @override     public boolean add(e e) {         super.add(e);         int = this.size() - 1;         int parent;          while (i > 0) {             parent = this.getparentindex(i);              if (this.get(i).compareto(this.get(parent)) < 0) {                 this.swap(i, parent);             } else {                 break;             }         }         return true;     }      public int getparentindex(int i) {         if (i % 2 == 1) {             return (i - 1) / 2;         } else {             return (i - 2) / 2;         }     }      private void swap(int i, int j) {         e temp = this.get(i);         this.set(i, this.get(j));         this.set(j, temp);     } } 

i warning @ compile-time:

minheap.java:21: warning: [unchecked] unchecked call compareto(t) member of raw type comparable             if (this.get(i).compareto(this.get(parent)) < 0) {                                  ^   t type-variable:     t extends object declared in interface comparable 1 warning 

which don't understand. missing?

i thought had needing check this.get(i) , this.get(parent) instances of comparable ... added check:

if (!(this.get(i) instanceof comparable) ||     !(this.get(parent) instanceof comparable)) {     return false; } 

but gives same warning.

public class minheap<e extends comparable> extends arraylist<e>  

should

public class minheap<e extends comparable<e>> extends arraylist<e>  

since comparable generic interface itself.