I am trying to add an integer to my database but it wont let me.
int count =0;
public void editHighScores(){
HashMap<String, String> queryValues = new HashMap<String, String>();
queryValues.put("totalWins", count);
myDatabase.insertHighScores(queryValues);
}
You have define the Map to accept String keys and String values, so you can'y put an int as value.
If you are not sure the value type, then Keep it as Object like
HashMap<String, Object> queryValues = new HashMap<String, Object>();
Or, if you know values will be always int only, then define like
HashMap<String, Integer> queryValues = new HashMap<String, Integer>();
Okay, HashMap is expecting two strings. Try doing HashMap<String, Integer> = new HashMap<String, Integer>();
Related
Im storing 2 map with different structure in single map like below,
Map<String, List<String>> colMap = new HashMap<String, List<String>>();
Map<String, String> appMap = new HashMap<String, String>();
// colMap assigning some values
// appMap assigning some values
Map<String, Map> mainMap = new HashMap<String, Map>();
mainMap.put("appMap", appMap);
mainMap.put("colMap", colMap);
I want to get map one by one and iterate the map.
If I try get map like below, getting error,
.......
Map colMap = map.get("colMap");
for(Entry<String, List<String>> entry : colMap.entrySet())
Error: Type mismatch: cannot convert from element type Object to Map.Entry<String,List<String>>
Why not just create a simple container POJO class (or record in Java 16+) for the two maps instead of mainMap and keep the relevant type-safety which to do it Java-way?
public class MapPojo {
private final Map<String, List<String>> colMap;
private final Map<String, String> appMap;
public MapPojo(Map<String, List<String>> colMap, Map<String, String> appMap) {
this.colMap = colMap;
this.appMap = appMap;
}
// getters, etc.
}
MapPojo mainMap = new MapPojo(colMap, appMap);
Error you are getting because when you are doing map.get operation your reference is Just Map without any Generics which will treated as Object class's reference. You should use generics like below and it will work -
Map<String, List<String>> colMap = map.get("colMap");
for(Entry<String, List<String>> entry : colMap.entrySet())
I have an outerMap which contains an innerMap for each key it got. At first, every innerMap is the same (here, they contain {1=1}.
I want to change the value of one certain innermap, for a certain key.
Here is my code:
public class HelloWorld
{
public static void main(String args[]){
HashMap<String, HashMap<String, Integer>> outerMap = new HashMap<String, HashMap<String, Integer>>();
HashMap<String, Integer> innerMap = new HashMap<String, Integer>();
outerMap.put("1001",innerMap);
outerMap.put("1002",innerMap);
outerMap.put("1003",innerMap);
innerMap.put("1", 1);
//My attempt to change only one innermap;
Map<String, Integer> map_to_change = outerMap.get("1001");
map_to_change.put("1", 0);
//And then I print them to see if it's working;
for(Map.Entry map : outerMap.entrySet() )
{
System.out.println(map.getKey()+" "+map.getValue());
}
}
}
However, the output here is
1003 {1=0}
1002 {1=0}
1001 {1=0}
Which shows that my code changes all innermaps, and not only the one linked with the key "1001".
What can I do?
You are pointing the same innerMap object in the outerMap,
outerMap.put("1001",new HashMap<String, Integer>());//create separate maps
outerMap.put("1002",new HashMap<String, Integer>());
outerMap.put("1003",new HashMap<String, Integer>());
HashMap<String, Integer> innerMap =outerMap.get("1001");//get the map you want to put value
innerMap.put("1", 1);//assign the value
Update:
If you want to retain a copy of Map which you have already created, you can copy and create a new Map from it using putAll method,
outerMap.put("1001",copyMap(innerMap));
outerMap.put("1002",copyMap(innerMap));
outerMap.put("1003",copyMap(innerMap));
copyMap method looks like,
private static HashMap<String, Integer> copyMap(HashMap<String, Integer> innerMap){
HashMap<String, Integer> copiedInnerMap = new HashMap<String, Integer>();
copiedInnerMap.putAll(innerMap);
return copiedInnerMap;
}
I have an ArrayList HashMap like the one below.
ArrayList<HashMap<String, String>> mArrType = new ArrayList<>();
with the following values added into it
HashMap<String, String> map;
map = new HashMap<String, String>();
map.put("type", "TRIMMER");
map.put("request", "5");
map.put("actual", "0");
mArrType.add(map);
map = new HashMap<String, String>();
map.put("type", "HAND ROUTER");
map.put("request", "6");
map.put("actual", "0");
mArrType.add(map);
map = new HashMap<String, String>();
map.put("type", "AIR COMPRESSOR");
map.put("request", "6");
map.put("actual", "0");
mArrType.add(map);
Question is how can i get the position of a hashmap from arraylist. eg : hashmap with 'type' trimmer has a position 0 in arraylist, I want to retrieve the position value "0"
I'll write a small util method
private static int getTrimmerTypeMapPosition(ArrayList<HashMap<String, String>> mArrType) {
for (int i = 0; i < mArrType.size(); i++) {
HashMap<String, String> mp = mArrType.get(i);
if (mp.get("type").equals("TRIMMER")) {
return i;
}
}
return -1;
}
To make this method very generic, have "type" and "TRIMMER" as method params, so that you can just pass any key and value pairs to check with.
That's not efficiently possible with your data structure. You can either store the own position in each HashMap or loop through all entries and search for the one with the type you are looking for.
You can, of course, define another HashMap<String, Integer> which maps all your type strings to the corresponding ArrayList index.
Others answer is also correct, but you can do this thing using Java8 also.
E.g.:
int index = IntStream.range(0, mArrType.size()).
filter(i -> mArrType.get(i).get("type").equals("TRIMMER"))
.findFirst().getAsInt();
I want to add an Arraylist<String> object(inputArrListObj) into my already existing Map<String, String> (param) which has some input values to be sent.
Map<String,String> param = new HashMap<String, String>();
List<String> obj = inputArrListObj;
param.put("1","Value");
//param.put("2",<Input list values>);
What should be the ideal approach to do the same?
It is not possible with your current declaration.
You must consider changing your map declaration to
Map<String,List<String>> param = new HashMap<String, List<String>>();
That allows you to insert a List as value.
However for the first case (param.put("1","Value");), your List will have only one String in it.
It's look like you want to store in your map abstract named values. If so try to use Map<String, Object> and cast to specific class when you get values from map.
Map<String, Object> param = new HashMap<String, Object>();
List<String> obj = inputArrListObj;
param.put("1", "Value");
param.put("2", obj);
...
List<String> param2 = (List<String>) param.get("2");
I have map of maps
Map<String, Map<String,Integer>> outerMap = new HashMap<String, Map<String, Integer>>();
and I want to put some values to inner map. Is that correct way? Or it can be done better?
class SampleMap {
Map<String, Map<String, Integer>> outerMap = new HashMap<String, Map<String, Integer>>();
public void add(String outerKey, String innerKey, Integer value) {
Map<String, Integer> tempMap = new HashMap<String, Integer>();
if (outerMap.size() > 0)
tempMap = outerMap.get(outerKey);
tempMap.put(innerKey, value);
outerMap.put(key, tempMap);
}
}
You can improve the code by avoiding the creation of a new inner map eagerly, until the point when you know that you must create it.
In addition, if you know that the inner map instance came from the outer map, you don't have to spend time putting it back where it came from.
public void add(String outerKey, String innerKey, Integer value) {
Map<String, Integer> tempMap
if (outerMap.containsKey(outerKey)) {
tempMap = outerMap.get(outerKey);
} else {
tempMap = new HashMap<String, Integer>();
outerMap.put(outerKey, tempMap);
}
tempMap.put(innerKey, value);
}
Technically there is nothing wrong in your code (except a minor improvement suggested by dasblinkenlight), but is map of maps what you really need?
If you want to read/write values by two keys, probably it's better to create map from pair of two keys (MultiKey or Pair implementation can be used) or another data structure (see this comment for details https://stackoverflow.com/a/3093993/554281)