java - Why does T extends Comparable <? super T> include T? Meaning includes Comparable<T>? -

class binarysearch<t extends comparable<? super t> > 

why t extends comparable <? super t> including t, meaning including comparable<t> , not super class hierarchy? confused on super keyword thought super include super class items. new java , in java book had following example:

this regarding method in class trying limit upper , lower bound of hierarchy using java.awt.component class had extends container

class customcomponent<t extends container> 

in class have following method

void describecomponent<customcomponent<? super jpasswordfield> ref) 

and goes on

note jpasswordfield, superclass of jtextfield, omitted in list of permissible objects.

from lower bounded wildcards, section of generics section of the java tutorial:

... lower bounded wildcard restricts unknown type a specific type or super type of type.

^{(bold mine, emphasis theirs)}

thus, set of classes match t extends comparable<t> subset of set of classes match t extends comparable<? super t>. wildcard ? super t matches t , superclasses of t.

in other words, assumption "super include super class items" incorrect.

your confusion in example may arise fact jtextfield superclass of jpasswordfield; in other words, jpasswordfield extends jtextfield. example match of following classes:

• javax.swing.jpasswordfield
• javax.swing.jtextfield
• javax.swing.jtextcomponent
• javax.swing.jcomponent
• java.awt.container
• java.awt.component
• java.lang.object

the example make more sense following:

void describecomponent(customcomponent<? super jtextfield> ref) {...} 

note jpasswordfield, subclass of jtextfield, omitted in list of permissible objects, because not superclass of jtextfield.