Spring EL中的类操作符

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://www.springframework.org/schema/beans" xmlns:p="http://www.springframework.org/schema/p"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">
    <bean id="saxophone" class="com.stono.sprtest.Saxophone"></bean>
    <bean id="cymbal" class="com.stono.sprtest.Cymbal"></bean>
    <bean id="duke" class="com.stono.sprtest.Duke">
        <property name="instruments">
            <set>
                <ref bean="saxophone"/>
                <ref bean="saxophone"/>
                <ref bean="cymbal"/>
                <null/>
            </set>
        </property>
        <property name="pi" value="#{T(java.lang.Math).PI}"/>
        <property name="name" value="#{saxophone.getName()}" />
        <property name="name2" value="#{saxophone.name}" />
        <property name="name3" value="#{saxophone.getName()?.toUpperCase()}" />
        <property name="name4" value="#{saxophone.name?.toUpperCase()}" />
    </bean>
</beans>