To be more precise, Java initially uses a linked list for nodes within a bin. If the number of items inside the bin crosses TREEIFY_THRESHOLD (which is 8), then

To be more precise, Java initially uses a linked list for nodes within a bin. If the number of items inside the bin crosses TREEIFY_THRESHOLD (which is 8), then that specific bin is converted into a RB tree. This is detailed in implementation notes comment here: https://github.com/openjdk/jdk/blob/56468c42bef8524e53a929dc2ae603cff05b55e3/src/java.base/share/classes/java/util/HashMap.java#L146 https://github.com/openjdk/jdk/blob/56468c42bef8524e53a929dc...