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)
This question is related to
java
collections
linkedhashmap
// 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);
}
}
In Java 8:
Map<String, List<String>> test1 = new LinkedHashMap<String, List<String>>();
test1.forEach((key,value) -> {
System.out.println(key + " -> " + value);
});
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>
.
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 unless you are not putting in the correct type in the map in the first place.
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.
Source: Stackoverflow.com