1：Android might decide to shut down a process at some point, when memory is low and required by other processes that are more immediately serving the user. Application components running in the process that』s killed are consequently destroyed. A process is started again for those components when there』s again work for them to do.
2：When users switch between apps, Android keeps apps that are not foreground in a least-recently used (LRU) cache.
As the system runs low on memory, it kills processes in the LRU cache beginning with the process least recently used. The system also accounts for processes that hold onto the most memory and can terminate them to free up RAM.
3：When the system begins killing processes in the LRU cache, it primarily works bottom-up. The system also considers which processes consume more memory and thus provide the system more memory gain if killed. The less memory you consume while in the LRU list overall, the better your chances are to remain in the list and be able to quickly resume.
