The advantages and disadvantages of HashMap expansion and ArryList expansion

HashMap expansion:

• advantage:
  1. Improved the load factor of the hash table: when expanding, HashMap recalculates hash values ​​and reallocates bucket bits, reducing the possibility of hash conflicts and improving query performance.
  2. Support more elements: Expansion allows HashMap to accommodate more elements, making it more efficient when storing large amounts of data.
• shortcoming:
  1. Memory consumption: Expansion requires reallocation of larger memory space, which may lead to increased memory usage, especially when the amount of data stored in HashMap is large.
  2. The expansion operation is time-consuming: The expansion process may take some time due to recalculation of hash values ​​and reallocation of bucket bits, especially if there are a large number of elements.

ArrayList expansion:

• advantage:
  1. Dynamic sizing: ArrayList expansion allows it to automatically resize as needed to accommodate more elements.
  2. Continuous memory allocation: The internal implementation of ArrayList uses continuous memory blocks. When expanding, you can simply allocate a larger memory block and copy existing elements to the new memory block, reducing the cost of moving elements.
• shortcoming:
  1. Performance overhead during expansion: When ArrayList expands, a larger memory block needs to be reallocated and existing elements copied to the new memory block. This process may require some time and computing resources.
  2. Frequent expansion leads to fragmentation: If ArrayList is frequently expanded, it may cause memory fragmentation, that is, there are a large number of discontinuous small memory spaces.