CODEWITHSUNDEEP
javaarraylisthashmap
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Reputation: 101

HashMap to ArrayList using resultSet values

I want to query sql statement and create a hashmap to store 2 values. One being id and other the name. Then I want to add it to an ArrayList. There's something wrong with my code and it doesn't match the specific types. I don't understand what's wrong with it. Could you please explain what I'm doing wrong here? As far as I'm aware you can't add a hashmap of type <String, String> to ArrayList but how can I achieve it in other way?

ArrayList<String> KEYWORDS = new ArrayList<String>();

String sql = "SELECT da_tag_name, da_tag_id FROM da_tags WHERE da_tag_type_id = 8";
PreparedStatement stmt = conn.prepareStatement(sql);
ResultSet resultSet = stmt.executeQuery();

while (resultSet.next()) {
    HashMap<String, String> row = new HashMap<String, String>();
    row.put(resultSet.getString(1).toString(), resultSet.getString(2).toString());
    KEYWORDS.add(row);
}

Upvotes: 0

Views: 1002

Answers (3)

Zaki Petrov
Zaki Petrov

Reputation: 86

The best thing you can do is to create a custom class that represent your database Keyword object. For example: 

class Keyword {

         private final long id;
         private final String name;

         public Keyword(long id, String name) {
              this.id = id;
              this.name = name;
         }

         public long getId() {
              return this.id;
         }

         public String getName() {
              return this.name;
         }
    }

Also it is better to use the interface List instead of ArrayList. And then it goes like that: 

List<Keyword> keywords = new ArrayList<>();

Then in the while loop you can add all the keywords from the ResultSet

    while (resultSet.next()) {
         Keyword keyword = new Keyword(resultSet.getLong(2), resultSet.getString(1));
         keywords.add(keyword);
    }

Upvotes: 1

Ben Thurley
Ben Thurley

Reputation: 7141

There are a few problems with this code.

  1. The generic type for the List doesn't match what you're trying to add to it
  2. You should get in the habit of programming to the interface and not the implementation
  3. A variable should be camelCase (all uppercase is for constants)

Something like this: 

// Note: as of Java 7 you can simplify generics using the diamond operator   
List<Map<String, String>> keywords= new ArrayList<>();

String sql = "SELECT da_tag_name, da_tag_id FROM da_tags WHERE da_tag_type_id = 8";
PreparedStatement stmt = conn.prepareStatement(sql);
ResultSet resultSet = stmt.executeQuery();

while (resultSet.next()) {    
    Map<String, String> row = new HashMap<>();
    row.put(resultSet.getString(1).toString(), resultSet.getString(2).toString());    
    keywords.add(row);    
}

Finally I would consider the design and question the use of a HashMap that only ever has one entry.

Upvotes: 3

Ravi
Ravi

Reputation: 31397

You need to change 

ArrayList<String> keyword = new ArrayList<String>();

to 

ArrayList<HashMap<String, String>> keyword = new ArrayList<>();

Because, you are trying to add row, which is type of HashMap to List.

keyword.add(row);

Upvotes: 1

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