ArrayList删除重复元素

Question

我正在使用ArrayList将JSON数据解析为ListView，现在我想知道如何将remove duplicate条目从ArrayList填入ListView之前。

这是我的 JSON ：

{
  "data": [
    {
      "city": "Delhi"
    },
    {
      "city": "Mumbai"
    },
    {
      "city": "Delhi"
    },
    {
      "city": "Mumbai"
    }    
  ]
}

MainActivity.java

public class MainActivity extends Activity {

    ArrayList<Destination> destinationArrayList;    
    MainAdapter adapter;
    EditText editText;
    Destination destination;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        editText = (EditText) findViewById(R.id.editLocation);

        destinationArrayList = new ArrayList<Destination>();

        new JSONAsyncTask().execute("my api link");

        ListView listview = (ListView)findViewById(R.id.list);
        adapter = new MainAdapter(getApplicationContext(), R.layout.row, destinationArrayList);

        listview.setAdapter(adapter);                       
    }


    class JSONAsyncTask extends AsyncTask<String, Void, Boolean> {

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
        }

        @Override
        protected Boolean doInBackground(String... urls) {
            try {
                ....
                if (status == 200) {
                    HttpEntity entity = response.getEntity();
                    String data = EntityUtils.toString(entity);

                    JSONObject jsono = new JSONObject(data);
                    JSONArray jarray = jsono.getJSONArray("data");

                    for (int i = 0; i < jarray.length(); i++) {
                        JSONObject object = jarray.getJSONObject(i);

                        destination = new Destination();                                                
                        destination.setCity(object.getString("city"));                          
                        destinationArrayList.add(destination);

                    }
                    return true;
                }

            ......
            return false;
        }

        protected void onPostExecute(Boolean result) {
            adapter.notifyDataSetChanged();             
        }
    }

}

Answer 1

您可以使用HashSet。如果您使用模型类，则需要创建模型类的arraylist。

ArrayList<Destination> destinationArrayList = new ArrayList<Destination>();
Set<Destination> hashset = new HashSet<>(); 
hashset.addAll(destinationArrayList); 
destinationArrayList.clear(); 
destinationArrayList.addAll(hashset);

Answer 2

保留Set<String>城市名称。当您看到每个城市时，将其添加到集合中，然后仅在set.add(...)方法返回true时将其添加到列表中（从而表明它已添加到集合中，这意味着它之前不存在，这意味着这是你第一次看到这个城市。）

Answer 3

您可以将ArrayList传递给HashSet，并且将处理重复的元素。

Answer 4

如果您使用HashSet，则会删除重复项：

HashSet<string> hashset = new HashSet<>(destinationArrayList);

hashset将有一个唯一的列表

Answer 5

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    editText = (EditText) findViewById(R.id.editLocation);

    destinationArrayList = new ArrayList<Destination>();

    new JSONAsyncTask().execute("my api link");
    Set<String> hs = new HashSet<>();
    hs.addAll(destinationArrayList );
    destinationArrayList .clear();
    destinationArrayList .addAll(hs);

    ListView listview = (ListView)findViewById(R.id.list);
    adapter = new MainAdapter(getApplicationContext(), R.layout.row, destinationArrayList);

    listview.setAdapter(adapter);                       
}    

Answer 6

你能试试吗

public static void main( String[] args )
{

    List<String> withDuplicatesCities = new ArrayList<String>();
    withDuplicatesCities.add( "Dehli" );
    withDuplicatesCities.add( "Mumbai" );
    withDuplicatesCities.add( "Dehli" );
    withDuplicatesCities.add( "Mumbai" );

    List<String> withoutDuplicates = removeDuplicates( withDuplicatesCities );
    System.out.println( withoutDuplicates );

}

private static List<String> removeDuplicates( List<String> withDuplicatesCities )
{
    Set<String> set = new TreeSet<String>();
    List<String> newList = new ArrayList<String>();

    for( String city : withDuplicatesCities )
    {
        set.add( city );
    }
    newList.addAll( set );

    return newList;
}

Answer 7

使用此

HashSet<String> hs=new HashSet<>(list);