Memory performance is an important design issue for contemporary systems given the ever increasing memory gap. This paper proposes a space-efficient Java object model for reducing the memory consumption of 64-bit Java virtual machines. We propose Selective Typed Virtual Addressing (STVA) which uses typed virtual addressing (TVA) or implicit typing for reducing the header of 64-bit Java objects. The idea behind TVA is to encode the object?s type in the object?s virtual address. In other words, all objects of a given type are allocated in a contiguous memory segment. As such, the type information can be removed from the object?s header which reduces the number of allocated bytes per object. Whenever type information is needed for the given object, masking is applied to the object?s virtual address. Unlike previous work on implicit typing, we apply TVA to a selected number of frequently allocated and/or long-lived object types. This limits the amount of memory fragmentation. We implement STVA in the 64-bit version of the Jikes RVM on an AIX IBM platform and compare its performance against a traditional VM implementation without STVA using a multitude of Java benchmarks. We conclude that STVA reduces memory consumption by on average 15.5% (and up to 39% for some benchmarks). In terms of performance, STVA generally does not affect performance, however for some benchmarks we observe statistically significant performance speedups, up to 24%.