How to iterate through LinkedHashMap with lists as values
JavaCollectionsLinkedhashmapJava Problem Overview
I have following LinkedHashMap declaration.
LinkedHashMap<String, ArrayList<String>> test1
my point is how can i iterate through this hash map. I want to do this following, for each key get the corresponding arraylist and print the values of the arraylist one by one against the key.
I tried this but get only returns string,
String key = iterator.next().toString();
ArrayList<String> value = (ArrayList<String> )test1.get(key)
Java Solutions
Solution 1 - Java
for (Map.Entry<String, ArrayList<String>> entry : test1.entrySet()) {
String key = entry.getKey();
ArrayList<String> value = entry.getValue();
// now work with key and value...
}
By the way, you should really declare your variables as the interface type instead, such as Map<String, List<String>>
.
Solution 2 - Java
I'm assuming you have a typo in your get statement and that it should be test1.get(key). If so, I'm not sure why it is not returning an ArrayList
This should work:
// populate the map
Map<String, List<String>> test1 = new LinkedHashMap<String, List<String>>();
test1.put("key1", new ArrayList<String>());
test1.put("key2", new ArrayList<String>());
// loop over the set using an entry set
for( Map.Entry<String,List<String>> entry : test1.entrySet()){
String key = entry.getKey();
List<String>value = entry.getValue();
// ...
}
or you can use
// second alternative - loop over the keys and get the value per key
for( String key : test1.keySet() ){
List<String>value = test1.get(key);
// ...
}
You should use the interface names when declaring your vars (and in your generic params) unless you have a very specific reason why you are defining using the implementation.
Solution 3 - Java
In Java 8:
Map<String, List<String>> test1 = new LinkedHashMap<String, List<String>>();
test1.forEach((key,value) -> {
System.out.println(key + " -> " + value);
});
Solution 4 - Java
You can use the entry set and iterate over the entries which allows you to access both, key and value, directly.
for (Entry<String, ArrayList<String>> entry : test1.entrySet()) {
System.out.println(entry.getKey() + "/" + entry.getValue());
}
> I tried this but get only returns string
Why do you think so? The method get
returns the type E
for which the generic type parameter was chosen, in your case ArrayList<String>
.
Solution 5 - Java
// iterate over the map
for(Entry<String, ArrayList<String>> entry : test1.entrySet()){
// iterate over each entry
for(String item : entry.getValue()){
// print the map's key with each value in the ArrayList
System.out.println(entry.getKey() + ": " + item);
}
}