参见EJB2.0规范，关于静态方法和属性:
24.1.2 Programming restrictions
• An enterprise Bean must not use read/write static fields. Using read-only static fields is allowed. Therefore, it is recommended that all static fields in the enterprise bean class be declared as final.
This rule is required to ensure consistent runtime semantics because while some EJB Containers may use a single JVM to execute all enterprise bean’s instances, others may distribute the instances across multiple JVMs.
• An enterprise Bean must not use thread synchronization primitives to synchronize execution of multiple instances.
Same reason as above. Synchronization would not work if the EJB Container distributed enterprise bean’s instances across multiple JVMs.
24.1.2 Programming restrictions
• An enterprise Bean must not use read/write static fields. Using read-only static fields is allowed. Therefore, it is recommended that all static fields in the enterprise bean class be declared as final.
This rule is required to ensure consistent runtime semantics because while some EJB Containers may use a single JVM to execute all enterprise bean’s instances, others may distribute the instances across multiple JVMs.
• An enterprise Bean must not use thread synchronization primitives to synchronize execution of multiple instances.
Same reason as above. Synchronization would not work if the EJB Container distributed enterprise bean’s instances across multiple JVMs.
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