Here is what I'm trying to do.
Map<String, List<Address>> mapObj = someService.getSomeAddress();
Using above call I'm getting mapObj of type Map<String, List<Address>>
And I want to send mapObj as a parameter in a another method (that I cannot change) as a LinkedHashMap<String, List<LinkedHashMap>> which does some further processing.
Is there any way that I can solve this problem without affecting data inside mapObj?
You will need to perform a couple of conversion steps.
Convert all Address objects to LinkedHashMap objects.
Put all Map entries into a LinkedHashMap object.
For 1st one, you can write a utility method some where that can do this conversion. For example,
public static List<LinkedHashMap> addresstoMap(List<Address> addresses)
{
List<LinkedHashMap> list = new ArrayList<>();
for(Address a: addresses){
LinkedHashMap map = new LinkedHashMap();
// Add address fields to map here
list.add(map);
}
return list;
}
Then, for the 2nd step, you can do this:
LinkedHashMap<String, List<LinkedHashMap>> map = new LinkedHashMap<?,?>();
iterate through the entry sets of mapObj and put them into the above map object.
for (Map.Entry<String, List<Address>> e : m.entrySet()) {
map.put(e.getKey(), addresstoMap(e.getValue()));
}
The final map object above will contain the correct representation in the LinkedHashMap<String, List<LinkedHashMap>> datatype.
Hope this helps!
Related
I have method that should return Map<Strings, List<String>> but in the mean time my method gives me a Map<Strings, Object>, I want to transfer the values of object into a List of Strings.
Here is the current code:
#SuppressWarnings("unchecked")
static Map<String, List<String>> getQueryParameters(JsonObject inputJsonObject) {
JsonArray parameters = inputJsonObject.getJsonArray("parameters");
Optional<JsonObject> queryParameters = parameters.stream().
filter(JsonObject.class::isInstance).
map(JsonObject.class::cast).
filter(jsonObject -> jsonObject.getJsonObject("queryParameters") != null).
map(item -> item.getJsonObject("queryParameters")).findFirst();
Map<String, Object> paramMap = queryParameters.get().getMap();
paramMap contains key and value , values could be an arrays of integers
so I want to put them into the map below:
Map<String, List<String>> mystore = new LinkedHashMap<String, List<String>>();
My solution is this which did not work correctly
Map<String, List<String>> mystore = new LinkedHashMap<String, List<String>>();
Map<String, Object> paramMap = queryParameters.get().getMap();
Iterator it = paramMap.entrySet().iterator();
while (it.hasNext()) {
String key = it.next().toString();
if (!mystore.containsKey(key)) ;
mystore.put(key, new LinkedList<String>());
mystore.get(key).add(it.next().toString());
}
I was a key holding another key as value and is just a mix up , any suggestions?
After debuging what happens i see that mystore holds both "key and value" together as a key and value it hold the next "key and value as value
Should be something like this:
while (it.hasNext()) {
Map.Entry<String, Object> next = iterator.next();
String key = next.getKey();
Object value = next.getValue();
if (!mystore.containsKey(key)) mystore.put(key, new LinkedList<String>());
mystore.get(key).add(value.toString());
}
I'm not writing a program for you, but instead help you in finding a problem. You are confused with Entry. If you are using IDE, you should solve it easier. Look for this line :
String key = it.next().toString();
Entry has a K,V pair. The iterator returns an EntrySet and thus usage to get key is it.next().getKey() and it.next().getValue()
Now that you have a correct key, please go on debugging. Instead of putting and getting and manipulating in below lines of your code. Put with correct value instead?
Yours:
mystore.put(key, new LinkedList<String>());
mystore.get(key).add(it.next().toString());
What about?:
Entry entry = it.next();
//Get key and value here. DO coding using Entry's methods
List<String> ll = new LinkedList<String>();
ll.add(value)
mystore.put(key, ll);
Tip: Always have the Javadoc or reference documentation handy for knowing more. That's how you learn the language. Refer:https://docs.oracle.com/javase/7/docs/api/java/util/Map.Entry.html
For example, I want to create a map that is a map of a map of a map. So I have declared the map as so. From a resultset I want to create a JSON object.
Map<String, Map<String, Map<String, String>>> data = new LinkedHashMap<String, Map<String, Map<String, String>>>();
I could define as
Map<String, Object> map = new LinkedHashMap<String, Object>();
however I need to put items one at a time so I get the map I want and put it in. Then the same the following iterations so I would have to cast the object to the map which leaves unchecked warnings.
Is there a better way of declaration of this type of Collection?
You can use a Google Guava MultiMap, but really you're better off creating a new Object and referencing the entire collection of data from the single key.
public class MyObjectData {
private String string1;
private Map<String, String> map;
// Getters and setters
}
Then your map becomes Map<String, MyObjectData>
I have the following data structure:
Map<String,Map<String,String>>
I'd like to extract its value (which itself is another string Map) from this complex Map object. I am currently doing it as such:
Map<String, Map<String, String>> map = getStructure(data,format);
Map<String,String> newMap = new LinkedHashMap<String, String>();
for(Entry<String, Map<String,String>> entry : map.entrySet()) {
for (Entry<String, String> value : entry.getValue().entrySet()) {
newMap.put(value.getKey(),value.getValue());
}
}
The above implementation gives me a new Map object with repeating key-value pairs due to the outer foreach loop, it is iterating through. Seems like I'm missing something.
How can I extract the inner Map object from the complex Map object?
Edit:
Addressing AlexWien's comment
Original Data Structure:
The reasoning behind the original data structure is to store a single value for a pair of IDs (ID1 and ID2). ID1 and ID2 may be different. So it is structured as:
Map<String,Map<String,String>> ===> <someValue, <ID1,ID2>>
What I am trying to achieve is to get the entire list of the id pairs (ID1 and ID2) for every someValue. So I can store them in a database to keep track of aeronautical information.
Having an map of maps:
Map<String, Map<String, String>> map
you get the inner map simply by calling get
String key = ...; // TODO
Map<String, String> innerMap = map.get(key);
Update to your edit:
It further seems you need something like a map of pairs:
Map<String, Pair<String, String>> mapOfPairs.
Unfortuneatly java has no Pair class.
So write one yourself:
public class Pair {
String id1;
String id2;
}
and have a
Map<String, Pair> mapOfPairs;
I have this ArrayList
public ArrayList<HashMap<String, String>> xmlFileNames = new ArrayList<>();
and I want to convert this to:
HashMap<String, String> comparemap2 = new HashMap<>();
What I want is: I want all the Items inside the ArrayList and want to put them into the HashMap
My HashMap looks like:
KEY VALUE
job_id 032014091029309130921.xml
job_id 201302149014021492929.xml
job_id 203921904901920952099.xml
EDIT:
Later I want to compare this map with an existing map:
Properties properties = new Properties();
try {
properties.load(openFileInput("comparexml.kx_todo"));
} catch (IOException e) {
e.printStackTrace();
}
for (String key : properties.stringPropertyNames()) {
compareMap.put(key, properties.get(key).toString());
}
HashMap<String, String> oldCompareMap = new HashMap<>();
for (HashMap key : xmlFileNames) {
oldCompareMap.putAll(key);
}
isEqualMaps(oldCompareMap, compareMap);
I only want to compare, if the filename exists in the compareMap. If not, than add it to the xmlFileName Map
I've looked up in StackOverFlow, how I can convert ArrayList to HashMap. But the other Threads treat data types like Item or Product.
I hope you can help me!
Kind Regards
Given...
public ArrayList<HashMap<String, String>> xmlFileNames = new ArrayList<>();
then something like this should do it.
HashMap<String, String> nhm = new HashMap<>();
for (HashMap xmlFileHm : xmlFileNames ) {
nhm.putAll(xmlFileHm);
}
but be aware if you have duplicate keys in your hashmaps they will get overwritten.
You should also think about coding to interfaces. Take a look at Map and List rather than typing your collections to implementations (ArrayList and HashMap). Take a look at this thread which is quite interesting What does it mean to "program to an interface"?
Depending on what you are trying to do as well you might consider a MultiMap as this might server your purposes better
Edit After update to the question...
A multimap would be better here with one key and multiple values. Although arguably if the key never changes then you could just store the values in a list. For multiamps you can use Google's guava library or do one yourself. For example (not checked for compilation errors as Im doing this from my head)
Map<String, List<String>> m = new HashMap<>();
if (m.containsKey("key")) {
m.get("key").add("new value");
}
else {
List<String> l = new ArrayList<>();
l.add("new value");
m.put("key", l);
}
You can create a new HashMap, then iterate through the list and put all elements from the map from the list to the main map.
List<Map<String, String>> list = new ArrayList<>();
Map<String, String> map = new HashMap<>();
for (Map<String, String> mapFromList : list) {
map.putAll(mapFromList);
}
You can try something like this..
ArrayList<HashMap<String, String>> xmlFileNames = new ArrayList<>();
HashMap<String, String> comparemap2 = new HashMap<>();
for(HashMap<String, String> i:xmlFileNames){
comparemap2.putAll(i);
}
You may need to consider the case of duplicate keys. else they will get override.
Create a new map and put All each element of arrayList to the map.
But in that case if you have same keys in two element of arrayList (hashmap) then it will override the previous one.
I have got some troubles converting each value in my HashMap to a String.
private static HashMap<String, List<Music>> musiksammlung = new
HashMap<String, List<Music>>();
This is my constructor for the HashMap. The key represents the album, the value a list of tracks from this album.
Now I want to convert each Music object to a String without creating a new HashMap, is this
possible?
I've tried it with the Iterator scheme, for loop over the entry set and so on but nothing seems to work.
Edit://
My code for the convertmethod:
public HashMap<String, List<String>> generateFormatList() {
HashMap<String, List<String>> formatList = new HashMap<String, List<String>>();
for(String key : musiksammlung.keySet())
formatList.put(key, musiksammlung.get(key).toString());
return musiksammlung;
}
But this always results in an error "is not applicable for the Arguments (String, String) so I have no idea. Do I have to override toString()?
You're on the right path but you need to convert the existing List<Music> to a List<String> and put the List<String> into your new HashMap.
You also then want to return your newly created HashMap<String, List<String>> instead of your original one.
public HashMap<String, List<String>> generateFormatList() {
HashMap<String, List<String>> formatList = new HashMap<String, List<String>>();
for(String key : musiksammlung.keySet()) {
// Value to store in map
List<String> value = new ArrayList<String>();
// Get the List<Music>
List<Music> musicList = musiksammlung.get(key);
for (Music m: musicList) {
// Add String of each Music object to the List
value.add(m.toString);
}
// Add the value to your new map
formatList.put(key, value);
}
// Return the new map
return formatList;
}
So answer your question:
Now I want to convert each Music object to a String without creating a
new HashMap, is this possible?
You need to create a new HashMap, because it's storing different type of value: List<Music> is different from List<String>.
Also as mentioned in my previous answer, make sure you override Music.toString() so that it returns a meaningful String for you instead of the one it inherits from its parent classes, which includes at least java.lang.Object
formatList wants a List<String>, but musiksammlung.get(key).toString() returns a String (not a List<String>). Did you mean this?
HashMap<String, String> formatList = new HashMap<String, String>();
Have you tried something like this:
Iterator<String> it = musiksammlung.keySet().iterator();
while (it.hasNext()) {
List<Music> ml = musiksammlung.get(it.next());
for (Music m : ml)
System.out.println(m.toString());
}
And of course you should override the Music#toString() method with something you could use.
Try to change your HashMap like this:
private static HashMap<String, List<Object>> musiksammlung = new HashMap<String,List<Object>>();
So you can save any kind of objects in this HashMap. Also use instanceof to check the type of the object before using it.