A system and method for use with garbage collected systems and languages, for enabling an allocated heap memory to be updated (e.g., increased or decreased) at runtime, subject to sufficient availability of physical memory. In accordance with an embodiment, a Java Virtual Machine (JVM) is associated with a management console, which allows a systems administrator to monitor current heap utilization at runtime. The heap is visualized as a contiguous chunk of memory with one or more extension points, e.g., by use of a trailing pointer to a null list. If later, at runtime, the heap size needs to be incremented then the trailing pointer can be set to a new chunk of memory with a size of (new value−old value), so that the cumulative new size is made equal to a new value specified on the console. The new chunk of memory can again end with a trailing pointer, to allow for further extension. The features can help ensure that an alert administrator will have the means to prevent an out-of-memory situation when the allocated heap proves insufficient at runtime.