I need to convert a HashMap<String, Object> to an array; could anyone show me how it's done?

14 Answers

hashMap.keySet().toArray(); // returns an array of keys hashMap.values().toArray(); // returns an array of values 

Edit

It should be noted that the ordering of both arrays may not be the same, See oxbow_lakes answer for a better approach for iteration when the pair key/values are needed.

If you want the keys and values, you can always do this via the entrySet:

hashMap.entrySet().toArray(); // returns a Map.Entry<K,V>[] 

From each entry you can (of course) get both the key and value via the getKey and getValue methods

If you have HashMap<String, SomeObject> hashMap then:

hashMap.values().toArray(); 

Will return an Object[]. If instead you want an array of the type SomeObject, you could use:

hashMap.values().toArray(new SomeObject[0]); 

To guarantee the correct order for each array of Keys and Values, use this (the other answers use individual Sets which offer no guarantee as to order.

Map<String, Object> map = new HashMap<String, Object>(); String[] keys = new String[map.size()]; Object[] values = new Object[map.size()]; int index = 0; for (Map.Entry<String, Object> mapEntry : map.entrySet()) { keys[index] = mapEntry.getKey(); values[index] = mapEntry.getValue(); index++; } 

An alternative to CrackerJacks suggestion, if you want the HashMap to maintain order you could consider using a LinkedHashMap instead. As far as im aware it's functionality is identical to a HashMap but it is FIFO so it maintains the order in which items were added.

I used almost the same as @kmccoy, but instead of a keySet() I did this

hashMap.values().toArray(new MyObject[0]); 

If you are using Java 8+ and need a 2 dimensional Array, perhaps for TestNG data providers, you can try:

map.entrySet() .stream() .map(e -> new Object[]{e.getKey(), e.getValue()}) .toArray(Object[][]::new); 

If your Objects are Strings and you need a String[][], try:

map.entrySet() .stream() .map(e -> new String[]{e.getKey(), e.getValue().toString()}) .toArray(String[][]::new); 

Map<String, String> map = new HashMap<String, String>(); map.put("key1", "value1"); map.put("key2", "value2"); Object[][] twoDarray = new Object[map.size()][2]; Object[] keys = map.keySet().toArray(); Object[] values = map.values().toArray(); for (int row = 0; row < twoDarray.length; row++) { twoDarray[row][0] = keys[row]; twoDarray[row][1] = values[row]; } // Print out the new 2D array for (int i = 0; i < twoDarray.length; i++) { for (int j = 0; j < twoDarray[i].length; j++) { System.out.println(twoDarray[i][j]); } } 

To Get in One Dimension Array.

 String[] arr1 = new String[hashmap.size()]; String[] arr2 = new String[hashmap.size()]; Set entries = hashmap.entrySet(); Iterator entriesIterator = entries.iterator(); int i = 0; while(entriesIterator.hasNext()){ Map.Entry mapping = (Map.Entry) entriesIterator.next(); arr1[i] = mapping.getKey().toString(); arr2[i] = mapping.getValue().toString(); i++; } 

To Get in two Dimension Array.

 String[][] arr = new String[hashmap.size()][2]; Set entries = hashmap.entrySet(); Iterator entriesIterator = entries.iterator(); int i = 0; while(entriesIterator.hasNext()){ Map.Entry mapping = (Map.Entry) entriesIterator.next(); arr[i][0] = mapping.getKey().toString(); arr[i][1] = mapping.getValue().toString(); i++; } 

In the case keys and values are strings and you want to alternate key and value in the same array:

String[] result = myMap.entrySet() .stream() .flatMap(entry -> Stream.of(entry.getKey(),entry.getValue())) .toArray(String[]::new); // result = {key_1, value_1, key_2, value_2 ...} 

You may try this too.

public static String[][] getArrayFromHash(Hashtable<String,String> data){ String[][] str = null; { Object[] keys = data.keySet().toArray(); Object[] values = data.values().toArray(); str = new String[keys.length][values.length]; for(int i=0;i<keys.length;i++) { str[0][i] = (String)keys[i]; str[1][i] = (String)values[i]; } } return str; } 

Here I am using String as return type. You may change it to required return type by you.

@SuppressWarnings("unchecked") public static <E,T> E[] hashMapKeysToArray(HashMap<E,T> map) { int s; if(map == null || (s = map.size())<1) return null; E[] temp; E typeHelper; try { Iterator<Entry<E, T>> iterator = map.entrySet().iterator(); Entry<E, T> iK = iterator.next(); typeHelper = iK.getKey(); Object o = Array.newInstance(typeHelper.getClass(), s); temp = (E[]) o; int index = 0; for (Map.Entry<E,T> mapEntry : map.entrySet()) { temp[index++] = mapEntry.getKey(); } } catch (Exception e) { return null; } return temp; } //-------------------------------------------------------- @SuppressWarnings("unchecked") public static <E,T> T[] hashMapValuesToArray(HashMap<E,T> map) { int s; if(map == null || (s = map.size())<1) return null; T[] temp; T typeHelper; try { Iterator<Entry<E, T>> iterator = map.entrySet().iterator(); Entry<E, T> iK = iterator.next(); typeHelper = iK.getValue(); Object o = Array.newInstance(typeHelper.getClass(), s); temp = (T[]) o; int index = 0; for (Map.Entry<E,T> mapEntry : map.entrySet()) { temp[index++] = mapEntry.getValue(); } } catch (Exception e) {return null;} return temp; } 

HashMap<String, String> hashMap = new HashMap<>(); String[] stringValues= new String[hashMap.values().size()]; hashMap.values().toArray(stringValues); 

if you need to pass values to an array of objects try:

Array: Object[] object= hashMap.values().toArray(new Object[0]); Arraylist: ArrayList<Object> object=new ArrayList<>(hashMap.values());