java - How to properly cast expected generic-typed arguments? -

i'm lost in generics (java). real scenario involves jpa , criteriabuilder's

<y extends comparable<? super y>> predicate greaterthan(expression<? extends y> x, y y); 

but simplified same case in following class:

public class genericstest {      public class bean<t> {      };      public <t extends comparable<t>> t targetmethod(bean<t> bean, t object) {         return object;     }      @suppresswarnings("unchecked")     public <t> t casttogeneric(bean<t> bean, object object) {         return (t) object;     }      @suppresswarnings("unchecked")     public <t> void understandgenerics(bean<t> bean, object object) {         bean<comparable<t>> beanofcomparable = (bean<comparable<t>>) bean;         comparable<t> comparableobject = this.casttogeneric(beanofcomparable, object);         this.targetmethod(beanofcomparable, comparableobject);     }  } 

the invocation targetmethod(beanofcomparable, comparableobject) in last line generates

the method targetmethod(bean<t>, t) in type genericstest not applicable arguments (bean<comparable<t>>, comparable<t>)

and don't understand problem is, since t in targetmethod must comparable<t>, type i'm giving it.

the constraint on targetmethod thing causing fail:

public <t extends comparable<t>> t targetmethod(bean<t> bean, t object) 

when pass in variables (bean<comparable<x>>, comparable<x>), implying generic parameter t comparable<x> (i'm using x here distinguish between generic targetmethod , generic understandgenerics).

the constraint on targetmethod says when t comparable<x>, t must extend comparable<comparable<x>>. of course, not going satisfied.

i think intend better accomplished so:

@suppresswarnings("unchecked") public <t extends comparable<t>> void understandgenerics(bean<t> bean, object object) {     t comparable = (t) object;     targetmethod(bean, comparable); } 

notice added constraint t must comparable, whole process simpler. in general, pays limit unchecked code as possible, , put constraints on types instead.