I need to convert a HashMap<String, Object>
to an array; could anyone show me how it's done?
This question is related to
java
arrays
collections
hashmap
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]);
}
}
HashMap<String, String> hashMap = new HashMap<>();
String[] stringValues= new String[hashMap.values().size()];
hashMap.values().toArray(stringValues);
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
@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;
}
To guarantee the correct order for each array of Keys and Values, use this (the other answers use individual Set
s 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.
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]);
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.
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 Object
s are String
s and you need a String[][]
, try:
map.entrySet()
.stream()
.map(e -> new String[]{e.getKey(), e.getValue().toString()})
.toArray(String[][]::new);
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++;
}
Source: Stackoverflow.com