| Name | Description | Type | Package | Framework |
| FinalizablePhantomReference | Phantom reference with a finalizeReferent() method which a background thread invokes after the garbage collector reclaims the | Class | com.opensymphony.xwork2.inject.util | Apache Struts |
| FinalizableSoftReference | Soft reference with a finalizeReferent() method which a background thread invokes after the garbage collector reclaims the referent. | Class | com.opensymphony.xwork2.inject.util | Apache Struts |
| FinalizableWeakReference | Weak reference with a finalizeReferent() method which a background thread invokes after the garbage collector reclaims the referent. | Class | com.opensymphony.xwork2.inject.util | Apache Struts |
| Function | A Function provides a transformation on an object and returns the resulting object. | Interface | com.opensymphony.xwork2.inject.util | Apache Struts |
| ReferenceCache | Class | com.opensymphony.xwork2.inject.util | Apache Struts | |
| ReferenceMap | Concurrent hash map that wraps keys and/or values in soft or weak references. | Class | com.opensymphony.xwork2.inject.util | Apache Struts |
| ReferenceMap .Strategy | Interface | com.opensymphony.xwork2.inject.util.ReferenceMap | Apache Struts | |
| ReferenceType | Reference type. | Class | com.opensymphony.xwork2.inject.util | Apache Struts |
| Strings | Class | com.opensymphony.xwork2.inject.util | Apache Struts | |