Read HashMap<String, HashMap<Double, Integer>

Question

There is a HashMap:

HashMap aircraftHandling = new HashMap<String, HashMap<Double, Integer>>();

This HashMap contains the following entries:

HashMap<"M", HashMap<1.22, 200>>();
HashMap<"M", HashMap<5.62, 300>>();
HashMap<"L", HashMap<10.11, 900>>();

I need to get entries for the key "M", i.e. HashMap<1.22, 200> and HashMap<5.62, 300>. I do this in the following way:

HashMap lines = (HashMap<Double, Integer>) aircraftHandling.get("M");

The question is how to get Double and Integer, ie (1.22, 200) and (5.62, 300), into two separate variables?

for (int i=0; i<lines.size(); i++)
{
  //doubleValue = [i]???
  //integerValue = [i]???
}

You can't have two entries with the same key. The first will be overwrite. — GMZ
– GMZ, Commented Jun 21, 2013 at 8:29
@GMZ I believe that entries are inside map that is stored under "M" key. — Pshemo
– Pshemo, Commented Jun 21, 2013 at 8:31
In this example with one HashMap named aircraftHandling and three entries it will have only 2 entries because the first (HashMap<"M", HashMap<1.22, 200>>();) will be override by the second (HashMap<"M", HashMap<5.62, 300>>();). That's how I understud this question. — GMZ
– GMZ, Commented Jun 21, 2013 at 8:36
@GMZ You might be right, but there is also small chance that OP is using something like pastebin.com/mb53kYLx but he didn't described it correctly in his question. Anyway you are right about part that under one key there can be only one value. — Pshemo
– Pshemo, Commented Jun 21, 2013 at 8:42
The code you posted implies that your inner map will be better represented by it's own class instead of a key/value pair — Mataniko
– Mataniko, Commented Jun 21, 2013 at 8:51

AllTooSir · Accepted Answer · 2013-06-21 08:32:05Z

3

You can use an enhanced for loop just to read elements :

for (Map.Entry<Double, Integer> entry : lines.entrySet()) {
   Double key = entry.getKey();
   Integer value = entry.getValue();
}

This HashMap contains the following entries:

HashMap<"M", HashMap<1.22, 200>>();
HashMap<"M", HashMap<5.62, 300>>();
HashMap<"L", HashMap<10.11, 900>>();

I need to get entries for the key "M", i.e. HashMap<1.22, 200> and HashMap<5.62, 300>. I do this in the following way:

Not considering the syntax used , since the key is a String , the second time you try to put() a value in the Map using a String key which already exists in Map the new value will override the old value.

answered Jun 21, 2013 at 8:32

AllTooSir

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Comments

darijan · Accepted Answer · 2013-06-21 08:27:16Z

This is how you would extract a key-value pair of the HashMap by iterating over a keyset:

Iterator<Double> it= lines.keySet().iterator();
while (it.hasNext()) {
    Double key= it.next();
    Integer value= lines.get(key);
}

On the side note, I don't know if this is an error, or just a bad representation of your data:

HashMap<"M", HashMap<1.22, 200>>();
HashMap<"M", HashMap<5.62, 300>>();

But if it is how it looks, this is impossible. A Map can have a single value for a single key! That means, if you put some value for a key "M" and you do it again for the same key, the latter will overwrite the previous value. What you should do is:

//get the inner map for "M"
HashMap<Double, Integer> innerMap= aircraftHandling.get("M");
if (innerMap == null) {
    //if it does not exist instantiate it
    innerMap= new HashMap<Double, Integer>();
    aircraftHandling.put("M", innerMap);
}

and now, in the innerMap you add other values, e.g.:

innerMap.put(1.22, 200);
innerMap.put(5.62, 300);

Pshemo · Accepted Answer · 2013-06-21 08:30:30Z

2

Try maybe this way

Map<Double, Integer> lines = (HashMap<Double, Integer>) aircraftHandling.get("M");
// ^add this generic types here so you wont have to cast them later with getters
for (Map.Entry<Double, Integer> entry:lines.entrySet()){
    Double key = entry.getKey();
    Integer value = entry.getValue();
}

answered Jun 21, 2013 at 8:30

Pshemo

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Comments

maqjav · Accepted Answer · 2013-06-21 08:31:22Z

2

Here you have it:

HashMap<String, HashMap<Double, Integer>> aircraftHandling = new HashMap<String,    HashMap<Double, Integer>>();

HashMap<Double, Integer> subMap1 = new HashMap<Double, Integer>();
subMap1.put(1.22, 200);

HashMap<Double, Integer> subMap2 = new HashMap<Double, Integer>();
subMap1.put(5.62, 300);

aircraftHandling.put("M", subMap1);
aircraftHandling.put("L", subMap2);

HashMap<Double, Integer> lines = aircraftHandling.get("M");

for (Entry<Double, Integer> set : lines.entrySet()) {
    Double doubleValue = set.getKey();
    Integer integerValue = set.getValue();
}

answered Jun 21, 2013 at 8:31

maqjav

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Comments

Masudul · Accepted Answer · 2013-06-21 08:31:29Z

2

First, Map can't have duplicate key. If you insert duplicate key then previous one will disappear. You can use following code to separate key and value:

     HashMap lines = (HashMap<Double, Integer>) aircraftHandling.get("M");

     for(Map.Entry<Double, Integer> entry: lines ){

        doubleValue = entry.getKey();
        integerValue =entry.getValue();
     }

answered Jun 21, 2013 at 8:31

Masudul

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Comments

Arnaud Denoyelle · Accepted Answer · 2013-06-21 08:31:29Z

2

with a foreach loop and method HashMap.entrySet() :

HashMap<Double, Integer> map=...
for(Entry<Double,Integer> entry : map.entrySet()){
   Double d = entry.getKey();
   Integer i = entry.getValue();
}

answered Jun 21, 2013 at 8:31

Arnaud Denoyelle

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Comments

divyanshm · Accepted Answer · 2013-06-21 08:39:45Z

1

You cannot have 2 values for the key M. I hope you've taken care of that while putting the values. You should have put one hashmap for the value M.

You simply need to fetch the hashmap corresponding to key M

HashMap lines = (HashMap<Double, Integer>) aircraftHandling.get("M");

And then iterate over all entries in this map

Iterator it = lines.entrySet().iterator();
while (it.hasNext()) {
    Map.Entry pairs = (Map.Entry)it.next();
    double d = pairs.getKey().doubleValue();
    int i = pairs.getValue().intValue();
}

EDIT - Had answered from my mobile so missed a few details. Adding them now.

edited Jun 21, 2013 at 8:39

answered Jun 21, 2013 at 8:34

divyanshm

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