Java hardcoded switch vs hashmap

Question

Some Message class is able to return a tag name based on tag number

Since this class is instanciated many times, I am a bit reluctant to create a HashMap for each instance:

public class Message {
  private HashMap<Integer,String> tagMap;

  public Message() {
    this.tagMap = new HashMap<Integer,String>();
    this.tagMap.put( 1, "tag1Name");
    this.tagMap.put( 2, "tag2Name");
    this.tagMap.put( 3, "tag3Name");
  }

  public String getTagName( int tagNumber) {
    return this.tagMap.get( tagNumber);
  }
}

In favor of hardcoding:

public class Message {
  public Message() {
  }

  public String getTagName( int tagNumber) {
    switch( tagNumber) {
      case 1: return "tag1Name";
      case 2: return "tag2Name";
      case 3: return "tag3Name";
      default return null;
    }
  }
}

When you put everything in the mix ( Memory, Performance, GC, ...)

Is there any reason to stick to HashMap?

Answer 1

Initialize MAP in a static block.

And since you will be creating many objects of Message.you should write code like this

public class Message {

  private static HashMap tagMap;

  static {
     tagMap = new HashMap();
     tagMap.put( 1, "tag1Name");
     tagMap.put( 2, "tag2Name");
     tagMap.put( 3, "tag3Name");
  }

  public Message() {

  }

  public String getTagName( int tagNumber) {
    return tagMap.get( tagNumber);
  }
}

Answer 2

Map can be used as command pattern in which key represents condition and value represents command to be executed the only drawback is object gets created before used so if you have large number of such conditions then you can opt for map else switch is always elegant approach if your conditions are few.