java - How do I fix this bound mismatch error? -

by <item> it's saying : -

bound mismatch: type item not valid substitute bounded parameter <t extends   comparable<? super t>> of type expandablearraylist<t>  expandablearraylist<item> items = new expandablearraylist<item> (); 

these headers:

public interface listinterface <t extends comparable <? super t>> public class expandablearraylist<t extends comparable<?super t>>  extends item { public class item implements comparable 

i can't figure out need change exactly. every time change in 1 header other errors pop up. use compareto(object obj) type.

your item class implementing raw form of comparable interface. should have implement generic form, declaring type parameter on item itself. then, expandablearraylist can implement generic form of item.

public class item<t extends comparable <? super t>> implements comparable<t> 

and

public expandablearraylist<t extends comparable<?super t>>  extends item<t> 

this resolve compilation problems due headers.

but it's unclear why expandablearraylist should subclass item. should contain items; fails "is-a" test. expandablearraylist shouldn't extend item @ all.