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Java Java Data Structures Exploring the Java Collection Framework Maps

György Varga
György Varga
19,198 Points

Don't understand treetsByAuthor!


Can somebody please explain line by line what this code do in the video?

Map<String, List<Treet>> treetsByAuthor = new HashMap<String, List<Treet>>(); 
    for (Treet treet : treets) {
      List<Treet> authoredTreets = treetsByAuthor.get(treet.getAuthor());
      if (authoredTreets == null) {
        authoredTreets = new ArrayList<Treet>();
        treetsByAuthor.put(treet.getAuthor(), authoredTreets);
    System.out.printf("Treets by author: %s %n ", treetsByAuthor);
    System.out.printf("Treets by nickrp: %s %n ", treetsByAuthor.get("nickrp"));

Thank you very much!