Memory-efficient tail calls in the JVM with imperative functional objects. This paper presents FCore: a JVM implementation of system F with support for full tail-call elimination (TCE). Our compilation technique for FCore is innovative in two respects: it uses a new representation for first-class functions called imperative functional objects; and it provides a way to do TCE on the JVM using constant space. Unlike conventional TCE techniques on the JVM, allocated function objects are reused in chains of tail calls. Thus, programs written in FCore can use idiomatic functional programming styles, relying on TCE, and perform well without worrying about the JVM limitations. Our empirical results show that programs which use tail calls can run in constant space and with low execution time overhead when compiled with FCore.