java - 文字列を配列に追加し、配列リストを返す

Question

文字列 s をリスト配列に追加し、s を追加した後にリストを返し、arrayadapter に追加してリストビューに表示したいと考えています。

 ArrayList<String> arraylist;
 for (int i = 0; i < friendsData.length(); i++) 
 {
   JSONObject friend = friendsData.getJSONObject(i);
   String s=friend.getString("name");
   arraylist.add(s);
 }
 ArrayAdapter<String> adapter=new  ArrayAdapter(myactivity.this,android.R.layout.simple_list_item1,arraylist);
 listview.setAdapter(adapter);

しかし、リストビューにはアイテムが表示されず、エラーnull poiter.Help me.

Answer 1

ArrayList<String> arraylist;

You are just declaring a reference without creating the arraylist and making the reference pointing to it. However, what you need is:

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

where new ArrayList<String>(); creates the arraylist in the memory, and = makes the reference arraylist pointing to that arraylist.

Answer 2

You didn't initialize your arrayList

ArrayList<String> arraylist=new ArrayList<String>;

Answer 3

object must be initialized中古品です。

ArrayList<String> arraylist = new ArrayList<String>;