How to convert HashMap of objects to ArrayList of strings
I have it HashMap
like this:
Hashmap<String, Object> map = new Hashmap<String, Object>();
map.put(1, {id_student:"1;2;3"});
map.put(2, {id_student:"4;5"});
I want to get the values and put them in ArrayList
like:
array = [0] - 1
[1] - 2
[2] - 3
[3] - 4
[4] - 5
what i tried to do:
private Set<String> checked = new TreeSet<String>();
String idsAlunos = "";
for (Iterator<Map.Entry<String, GPSEscolas>> it = aMap.entrySet().iterator(); it.hasNext(); ) {
Map.Entry<String, GPSEscolas> entry = it.next();
String id_escola = entry.getKey();
String ids_aluno = entry.getValue().getAlunos();
idsAlunos += ";" + ids_aluno;
checked.add(idsAlunos.substring(1));
}
but I am getting this result from the code above: [4, 4;1;2;3, 4;5, 4;5;1;2;3]
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3 answers
You need to do it step by step:
- Iterate over the keys of the Map, or get the values of the Map as a Collection and repeat that.
- Separate each comma separated String value into separate tokens and add them to the list or set of values you want.
- Sorting the list of values after it appears.
Use Set if you don't have duplicates.
Similar to JSON. Are you using JSONSimple? Perhaps you should be.
Here's an example.
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
/**
* MapToArrayExample
* User: mduffy
* Date: 6/24/2015
* Time: 3:17 PM
* @link http://stackoverflow.com/questions/31034737/how-to-convert-a-hashmap-of-objects-into-an-arraylist-of-strings/31034794?noredirect=1#comment50094533_31034794
*/
public class MapToArrayExample {
public static void main(String[] args) {
Map<Integer, String> data = new HashMap<Integer, String>() {{
put(1, "3, 2, 3, 3, 1");
put(2, "4, 5, 5, 6, 7");
}};
List<String> result = parseMapOfJson(data);
System.out.println(result);
}
public static List<String> parseMapOfJson(Map<Integer, String> map) {
List<String> values = new ArrayList<String>();
for (Integer key : map.keySet()) {
String csv = map.get(key);
String [] tokens = csv.split(",");
for (String token : tokens) {
values.add(token.trim());
}
}
Collections.sort(values);
return values;
}
}
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Ok I figured it out like this:
idsAlunos = "";
for (Iterator<Map.Entry<String, GPSEscolas>> it = aMap.entrySet().iterator(); it.hasNext(); ) {
Map.Entry<String, GPSEscolas> entry = it.next();
String id_escola = entry.getKey();
String ids_aluno = entry.getValue().getAlunos();
idsAlunos += ";" + ids_aluno;
String[] array = idsAlunos.substring(1).split(";");
list = new ArrayList<String>(Arrays.asList(array));
}
System.out.println(list);
and this gives me what I want, namely: [4,5,1,2,3]
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Try the following:
HashMap<String, String> map = new HashMap<String, String>();
map.put("1", "1;2;3");
map.put("2", "4;5");
Set<String> checked = new TreeSet<String>();
for (Iterator i = map.entrySet().iterator(); i.hasNext();) {
Map.Entry<String, String> e = (Map.Entry<String, String>) i.next();
checked.addAll(Arrays.asList(e.getValue().split("\\s*;\\s*")));
}
System.out.println(checked);
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