How to use a declared array

Question

I can not do this it is showing this error:

I want to declare an array and then use it in while loop to assign a string variable in it.How can i do that?

package com.example.zaina.assignmentdb;

import android.database.Cursor;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.widget.ArrayAdapter;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.Toast;

import java.util.ArrayList;
import java.util.List;

public class Show extends AppCompatActivity {
    DB d=new DB(this);
    Cursor h;
    int j=0;
    String t;
    String []g;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_show);
        d.open();
        h=d.selectInfo();
        h.moveToFirst();
        while (h.moveToNext()){
            t=h.getString(j);
            g[]={t};
//            Toast.makeText(Show.this, t, Toast.LENGTH_SHORT).show();
        }
        ListAdapter listAdapter=new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1,g);
        ListView listView= (ListView) findViewById(R.id.listView);
        listView.setAdapter(listAdapter);
    }
}

`g[index here] = t`...You might consider using an `ArrayList` so you can dynamically add elements to it without knowing it's length before hand. — brso05, Jan 04 '17 at 18:26
first read this then you will come to know why compiler is complaining http://stackoverflow.com/questions/1200621/how-to-declare-an-array — RamPrakash, Jan 04 '17 at 18:27
Seconding RamPrakash. Read that article on how to declare arrays in Java. This will solve your issue. — Michael Dodd, Jan 08 '17 at 15:16

score 1 · Answer 1 · answered Jan 04 '17 at 20:15

1

I would use ArrayList<String> g = new ArrayList<>(); and then you can just use g.add("Your String")

it will also let you use a for each loop like so

for(String string : g) {Do something}

answered Jan 04 '17 at 20:15

HTMLlama

1,082
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score 0 · Answer 2 · answered Jan 04 '17 at 18:31

0

You could use an ArrayList and do something like this:

public class Show extends AppCompatActivity {
    DB d=new DB(this);
    Cursor h;
    int j=0;
    String t;
    ArrayList<String> g = new ArrayList<String>();
    String[] g1 = new String[1];
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_show);
        d.open();
        h=d.selectInfo();
        h.moveToFirst();
        while (h.moveToNext()){
            t=h.getString(j);
            g.add(t);
//            Toast.makeText(Show.this, t, Toast.LENGTH_SHORT).show();
        }
        g1 = (String [])g.toArray(g1);
        ListAdapter listAdapter=new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1, g1);
        ListView listView= (ListView) findViewById(R.id.listView);
        listView.setAdapter(listAdapter);
    }
}

answered Jan 04 '17 at 18:31

brso05

12,634
1
17
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I tried your'e code but it is giving error "Java null point exception",can you tell something?@brso05 – Zain Ul Abdin Jan 05 '17 at 12:41
it is not showing any line in android monitor,how should i send you a snapshot?@brso05 – Zain Ul Abdin Jan 05 '17 at 14:10
Process: com.example.zaina.assignmentdb, PID: 24557 java.lang.NullPointerException at android.widget.ArrayAdapter.createViewFromResource(ArrayAdapter.java:394)this is a small part of error which i am getting @brso05 – Zain Ul Abdin Jan 05 '17 at 14:16
@ZainUlAbdin is there anything in the `g1` array? – brso05 Jan 05 '17 at 18:17
Look i have a database and i want all the names it had to be shown in the form of list view that's what i am trying to do,so names will be added dynamically.But this code is showing error,i think g1 will have all names because we are assigning it here ' g1=(String[]) g.toArray(g1);'@brso05 – Zain Ul Abdin Jan 06 '17 at 09:00

score 0 · Answer 3 · answered Jan 04 '17 at 18:37

0

You forgot to initialize your variable g:

String[] g=new String[(Maximum index)]

answered Jan 04 '17 at 18:37

Tobi

116
4

How to use a declared array

3 Answers3