Get keys from hashmap and store in String array using java

Question

I have created one hashmap. All I need to do is get the keys from the hashmap and store in a String[] array.
This is what I was doing but it's not correct.

 HashMap<String, String> columnHeaders = new HashMap<String, String>();
        columnHeaders.put("Id", "101");
        columnHeaders.put("First Name","AAA");
        columnHeaders.put("Last Name","BBB");
        columnHeaders.put("Country","CCC");
        columnHeaders.put("City","DDD");
        columnHeaders.put("State","EEE");
        columnHeaders.put("Province","FFF");
}

 String[] keyHeaders=null;
            for(Map.Entry<String, String> param : columnHeaders.entrySet()){
            String key = param.getKey();
            keyHeaders = key.split(";");
            Arrays.toString(keyHeaders);
   }

I kept the String[] global because I need pass it to a for loop.
Could please someone help me with this?

Why are you splitting the key if none has ;? If you can use the keys as they are, just use String[] keyHeaders = columnHeaders.keySet().toArray(new String[0]);. — Thomas
– Thomas, Commented Aug 3, 2021 at 14:21
You are overthinking this way to much. HashMap already has a method to return a Set of your keys, and Set has a method to convert itself to an array: String[] keys = columnHeaders.keySet().toArray(new String[0]); — user6073886
– user6073886, Commented Aug 3, 2021 at 14:21
So I don't need this for each loop to iterate through the map? — XXXX
– XXXX, Commented Aug 3, 2021 at 14:33

WJS · Accepted Answer · 2021-08-03 14:29:26Z

1

You can do it like this.

HashMap<String, String> columnHeaders =
        new HashMap<String, String>();
columnHeaders.put("Id", "101");
columnHeaders.put("First Name", "AAA");
columnHeaders.put("Last Name", "BBB");
columnHeaders.put("Country", "CCC");
columnHeaders.put("City", "DDD");
columnHeaders.put("State", "EEE");
columnHeaders.put("Province", "FFF");

String[] keys = columnHeaders.keySet().toArray(String[]::new);

for (String k : keys) {
    System.out.println(k);
}

Prints

State
First Name
Country
Id
City
Last Name
Province

answered Aug 3, 2021 at 14:29

WJS

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2 Comments

Rajanboy Over a year ago

what do we mean by String[]::new inside toArray. would you please tell what does it have wrong String[] keys = columnHeaders.keySet().toArray()

WJS Over a year ago

Since the stream is of an Object, toArray would return an array of object (e.g. Object[]); But to change to a specific Object[] type you need to tell it which type. I could also have done String[] keys = columnHeaders.keySet().toArray(new String[0]). See the Collection Interface for more detail.

user16583109 · Accepted Answer · 2021-08-03 15:00:19Z

0

Try change 101 to "101" or String.value (101)

answered Aug 3, 2021 at 15:00

user16583109

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