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Difference between TreeMap, HashMap, and LinkedHashMap in Java
HashMap, TreeMap and LinkedHashMap all implements java.util.Map interface and following are their characteristics.
HashMap
HashMap has complexity of O(1) for insertion and lookup.
HashMap allows one null key and multiple null values.
HashMap does not maintain any order.
TreeMap
TreeMap has complexity of O(logN) for insertion and lookup.
TreeMap does not allow null key but allow multiple null values.
TreeMap maintains order. It stores keys in sorted and ascending order.
LinkedHashMap
LinkedHashMap has complexity of O(1) for insertion and lookup.
LinkedHashMap allows one null key and multiple null values.
LinkedHashMap maintains order in which key-value pairs are inserted.
Example
import java.util.HashMap;
import java.util.Hashtable;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.TreeMap;
public class Tester {
public static void main(String args[]) {
Map<String, String> map = new HashMap<String, String>();
map.put("One", "1");
map.put("Five", "5");
map.put("Four", "4");
map.put("Two", "2");
map.put("Three", "3");
System.out.println("HashMap: \n" + map);
Map<String, String> map1 = new LinkedHashMap<String, String>();
map1.put("One", "1");
map1.put("Five", "5");
map1.put("Four", "4");
map1.put("Two", "2");
map1.put("Three", "3");
System.out.println("LinkedHashMap: \n" + map1);
Map<String, String> map2 = new TreeMap<String, String>();
map2.put("One", "1");
map2.put("Five", "5");
map2.put("Four", "4");
map2.put("Two", "2");
map2.put("Three", "3");
System.out.println("TreeMap: \n" + map2);
}
}
Output
HashMap:
{Five = 5, One = 1, Four = 4, Two = 2, Three = 3}
LinkedHashMap:
{One = 1, Five = 5, Four = 4, Two = 2, Three = 3}
TreeMap:
{Five = 5, Four = 4, One = 1, Three = 3, Two = 2}
Here you see, HashMap has random order of Keys, LinkedHashMap has preserved the order in which keys are inserted and TreeMap has sorted order of keys.
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