spring jee problem

what's the different between proxy-interface and expected-type?

<jee:jndi-lookup id="tq" jndi-name="queue/testQueue"   
        cache="false"    
        expected-type="javax.jms.Queue"    
        lookup-on-startup="true"    
        proxy-interface="javax.jms.Queue"   
        resource-ref="false">   
        <jee:environment >      
		java.naming.factory.initial=org.jnp.interfaces.NamingContextFactory   
		java.naming.provider.url=jnp://localhost:1099   
		java.naming.factory.url.pkgs=org.jboss.naming:org.jnp.interfaces   
        </jee:environment>   
</jee:jndi-lookup>