Java Iteration through HashMap

Question

I'm struggling with a java HashMap. I want to return translationList as an array with strings. Example: word : "translated word".

Main class:

public static void main(String[] args) {
 Dictionary dictionary = new Dictionary();
 dictionary.add("apina", "monkey");
 dictionary.add("banaani", "banana");
 dictionary.add("cembalo", "harpsichord");
 ArrayList<String> translations = dictionary.translationList();
 for(String translation: translations) {
 System.out.println(translation);
 }
}

Dictionary class:

private HashMap<String, String> dictionary = new HashMap<String, String>();
public Dictionary(){};
public String translate(String word){
 if(dictionary.containsKey(word)){
 return dictionary.get(word);
 }
 return null;
}
public void add(String word, String translation){
 dictionary.put(word,translation);
}
public int amountOfWords() {
 return dictionary.size();
}
public ArrayList<String> translationList(){
 for ( String key : dictionary.keySet() ) {
 if(translationList().size()<dictionary.size()){
 translationList().add(key+" = "+dictionary.get(key));
 }
 }
 return translationList();
}

Java returns:

Exception in thread "main" java.lang.StackOverflowError
at java.base/java.util.HashMap$KeyIterator.<init>(HashMap.java:1515)
at java.base/java.util.HashMap$KeySet.iterator(HashMap.java:917)
at Dictionary.translationList(Dictionary.java:21)
at Dictionary.translationList(Dictionary.java:22)

Thanks for help :)

• RealSkeptic: You are calling your translationList() method instead of creating an actual list and adding to it. Why?
• Teifun2: If next time you include a runnable code, (with imports and class structure) help will be faster :)

Answer 1

Your translationList method is calling itself, leading to infinite recursive calls and StackOverflowError.

You probably intended to write something like:

public List<String> translationList(){
 List<String> list = new ArrayList<>();
 for ( String key : dictionary.keySet() ) {
 list.add(key+" = "+dictionary.get(key));
 }
 return list;
}

or

public List<String> translationList(){
 List<String> list = new ArrayList<>();
 for ( Map.Entry<String,String> entry : dictionary.entrySet() ) {
 list.add(entry.getKey()+" = "+entry.getValue());
 }
 return list;
}

You have to first create an ArrayList and then add Strings to it. Besides that, the if (translationList().size()<dictionary.size()) condition is pointless, even without the recursive call.

Answer 2

You're having a recursive call with return translationList();. This is probably accidental. Your code was probably intended to look something like:

public ArrayList<String> translationList(){
 List<String> translationList = new ArrayList<>();
 for ( String key : dictionary.keySet() ) {
 if(translationList().size()<dictionary.size()){
 translationList.add(key+" = "+dictionary.get(key));
 }
 }
 return translationList();
}

But an even simpler implementation can avoid extra lookups:

public List<String> translationList(){
 return dictionary.entrySet()
 .stream()
 .map(entry -> entry.getKey() + " = " + entry.getValue())
 .collect(Collectors.toList());
}