Comparison on HashMap, TreeMap, LinkedHashMap:
| HashMap | TreeMap | LinkedHashMap |
| No Duplicate Key are allowed, But values can be anything. | No Duplicate Key are allowed, But values can be anything. | No Duplicate Key are allowed, But values can be anything. |
| Orders cannot be predicted, in can print the data in any order | TreeMap will follow the natural ordering of key, All Keys in the TreeMap should be in same type | LinkedHashMap insertion order will be maintained, Adding duplicate key will not affect the existing order. |
| Supports 1 null Key | Does not support null key elements | Supports 1 null elements |
| Gives good performance on read and write | Slow when compared with HashMap, use this only when you need ordering by default | Slow when compared with HashMap, but faster than TreeMap, Use this if you need to maintain the insertion order of the data. |
Example:
package com.candidjava.core;
import java.util.HashMap;
import java.util.LinkedHashMap;
import java.util.TreeMap;
public class MapComparison {
public static void main(String[] args) {
HashMap<String, String> hm=new HashMap<String, String>();
hm.put("name","candid");
hm.put("email","candid@gmail.com");
hm.put("password", "123456");
hm.put("street", "shanthi nagar");
hm.put("password", "789");
hm.put("altemail", null);
hm.put("altph", null);
TreeMap<String, String> tm=new TreeMap<String, String>();
tm.putAll(hm);
LinkedHashMap<String, String> lhm=new LinkedHashMap<String, String>();
lhm.putAll(hm);
System.out.println("HashMap: " + hm);
System.out.println("TreeMap: " + tm);
System.out.println("LinkedHashMap: " + lhm);
}
}
Output:
HashMap: {password=789, altemail=null, street=shanthi nagar, name=candid, altph=null, email=candid@gmail.com}
TreeMap: {altemail=null, altph=null, email=candid@gmail.com, name=candid, password=789, street=shanthi nagar}
LinkedHashMap: {password=789, altemail=null, street=shanthi nagar, name=candid, altph=null, email=candid@gmail.com}