What is the difference between treemap and hashmap in java?

Difference: 1. The elements in HashMap have no order; all elements in TreeMap have a certain fixed order. 2. HashMap inherits the AbstractMap class and is implemented based on the hash table; TreeMap inherits the SortedMap class and is implemented based on the red-black tree.

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TreeMap and HashMap The difference

Map: In an array, its content is indexed through the array subscript, while in Map, the object is indexed through the object. The object used for indexing is called Key key, its corresponding object is called value;

1. HashMap uses hashcode() to quickly search its content; the elements in HashMap are not in order;

In TreeMap All elements have a certain fixed order. If you need to get an ordered result, you should use TreeMap;

2, HashMap and TreeMap are not thread-safe;

3 , HashMap inherits the AbstractMap class; it overrides the hashcode() and equals() methods to ensure that two equal mappings return the same hash value;

TreeMap inherits the SortedMap class; it maintains the ordered order of keys;

4. HashMap: implemented based on hash table; the key class required to be added using HashMap clearly defines hashcode() and equals() (this method can be overridden); in order to optimize the space usage of HashMap, you can adjust Optimize initial capacity and load factor;

TreeMap: implemented based on red-black tree; TreeMap has no tuning options, because red-black tree is always in a balanced state;

5, HashMap: Suitable for Map insertion, deletion, and positioning elements;

TreeMap: Suitable for traversing keys in natural order or custom order;

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