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Java Java Data Structures - Retired Exploring the Java Collection Framework Maps

edumorlom
edumorlom
4,073 Points
Posted by edumorlom
edumorlom
4,073 Points

Why is it sorting my HashMap automatically. I don't want that.

My code:

import java.util.*;
class Main {
  public static void main(String[] args) {
    Map<String, Integer> peopleByAge = new HashMap<String, Integer>();
    peopleByAge.put("Alvaro", 21);
    peopleByAge.put("Eduardo", 19);
    peopleByAge.put("Carlos", 13);
    peopleByAge.put("Pedro", 29);
    System.out.println(peopleByAge);
    for (Map.Entry mapEntry : peopleByAge.entrySet()){
        System.out.println(mapEntry.getKey() + " is " + mapEntry.getValue() + " years old");
    }
  }
}

The programs output is:

//Notice how I put Pedro after Carlos, yet HashMap is showing Pedro first.
{Eduardo=19, Alvaro=21, Pedro=29, Carlos=13}
Eduardo is 19 years old
Alvaro is 21 years old
Pedro is 29 years old
Carlos is 13 years old

Also, why is it that when I import java.util.HashMap instead of the entire java.util.* library, my code fails?

1 Answer

markmneimneh
markmneimneh
14,132 Points

Hello

re:

Why is it sorting my HashMap automatically. I don't want that.

Please read this ... http://beginnersbook.com/2013/12/hashmap-in-java-with-example/

the compiler, by design, does not guarantee that the order you get back when you print out a hashmap, is same as the one you put in.

Hashmap, by definition, is an un-ordered list of key-value items.

re: Also, why is it that when I import java.util.HashMap instead of the entire java.util.* library, my code fails?

probably it is failing because you also need:

import java.util.Map;

I see you are using Map in your example

If this answers the question, please mark the question as answered.

Thanks