How do I access the values in an object inside a HashMap

Question

I'm attempting to access values that are held inside a Class which is listed in a HashMap.

In my first class I create a HashMap which links to the "LiftingStats" class.

Map<String, LiftingStats> fitnessGoals = new HashMap<String, LiftingStats>();

In the LiftingStats class I do the following...

public class LiftingStats
{
   public String activity;
   public String weightType;
   public int weight;
   public double difficulty;

   /**
    * Constructor for objects of class LiftingStats
    */
   public LiftingStats()
   {
      this.run();
   }

   /**
    * test method to fill values
    */
   public void run(){
      //code
      this.activity = "bench press";
      this.weightType = "Kg";
      this.weight = 100;
      this.difficulty = 8.5;
   }

I'm running a test method to fill the hashmap with some values

   public void testMethod(){
      fitness.put("activityone", new LiftingStats());
      fitness.put("activitytwo", new LiftingStats());

`fitness.values()` gives you a `Collection`; just iterate that. — Andy Turner, Mar 14 '16 at 13:20
You are using the wrong terminology. You're title question should be: "How do I access the values in an *object* inside a HashMap?" — ControlAltDel, Mar 14 '16 at 13:21
What exactly are you trying to do? Read values from the `fitness` map (i.e. from the `activityone` `LiftingStats` object)? — Ori Lentz, Mar 14 '16 at 13:21
So the key is activityone & activitytwo - I want to get the instance variables that are in LiftingStats that are linked to activityone and activitytwo if that makes sense? — , Mar 14 '16 at 13:23

score 2 · Accepted Answer · answered Mar 14 '16 at 13:29

There are many ways to access them.

For retrieving the value of a specific key entry

LiftingStats valueForOne = fitness.get("activityone");

For retrieving values without concern for keys

Collection<LiftingStats> values = fitness.values();

For retrieving key and value pairs

Set<Map.Entry<String, LiftingStats>> entries = fitness.entrySet();
for (Map.Entry<String, LiftingStats> entry : entries) {
   entry.getValue();
}

or some variant.

score 1 · Answer 2 · answered Mar 14 '16 at 13:24

A Map is a Data Structure consisting of Key, Value pairs. In this case you have two keys that reference two instances of LiftingStats objects. To access these objects simply use your specific key to retrieve the object(s). Ex:

LiftingStats current = fitness.get("activityone");

With your reference to current you can perform operations on that specific LiftingStats object.

Similarly, you can 'daisy-chain' function calls together like this and still mutate the object within the Map. Ex:

fitness.get("activityone").someMethod();

score 1 · Answer 3 · edited May 23 '17 at 10:28

1

You can adapt this answer to your problem : How to efficiently iterate over each Entry in a Map?

Map<String, LiftingStats> fitnessGoals = new HashMap<String, LiftingStats>();
for (Map.Entry<String, LiftingStats> entry : fitnessGoals.entrySet())
{
    //What you need to do with your map
}

edited May 23 '17 at 10:28

Community

1
1

answered Mar 14 '16 at 13:27

Laurent-P

145
1
9

score 0 · Answer 4 · answered Feb 24 '21 at 06:58

Another way by which you can access variables of an object in HashMap is by typecasting the data fetched by getValue() method of a Hashmap into the user defined class.

You can use the following code:

Map<String, LiftingStats> lstats= new HashMap<String, LiftingStats>();
for (Map.Entry ls:lstats.entrySet()) {
    System.out.println(ls.getKey()+" "+((LiftingStats)ls.getValue()).activity);
}

Any variable present in the class can be accessed simply by using ((LiftingStats)ls.getValue()).Var_name . where Var_name is the name of any class variable.

How do I access the values in an object inside a HashMap

4 Answers4