MainActivity

package com.example.a07act;

import android.content.ContentValues;
import android.os.Bundle;
import android.widget.TextView;

import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {

    TextView one, two, three, four;
    SqliteHelper sqliteHelper;
    SqliteHelper.Queries query;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        sqliteHelper = new SqliteHelper(this);
        query = new SqliteHelper.Queries(this);

        SetUIVariables();
        populateData();
        setDataOne();
        setDataTwo();
        setDataThree();
        setDataFour();
    }

    void setDataOne() {
        String s = "";
        for (String x : query.retrieveItemCode()) {
            s += x + "\n";
        }
        one.setText(s);
    }

    void setDataTwo() {
        String s = "";
        for (String x : query.retrieveAllCol()) {
            s += x + "\n";
        }
        two.setText(s);
    }

    void setDataThree() {
        String s = "";
        for (String x : query.retrieveAllCol(75)) {
            s += x + "\n";
        }
        three.setText(s);
    }

    void setDataFour() {
        query.changePrice(101, 75);
        String s = "";
        for (String x : query.retrieveAllCol()) {
            s += x + "\n";
        }
        four.setText(s);
    }

    void populateData() {
        ContentValues[] values = new ContentValues[4];
        values[0] = new ContentValues();
        values[0].put("ItemCode", 50);
        values[0].put("ItemDesc", "Laptop");
        values[0].put("Price", 150);

        values[1] = new ContentValues();
        values[1].put("ItemCode", 63);
        values[1].put("ItemDesc", "Mouse");
        values[1].put("Price", 20);

        values[2] = new ContentValues();
        values[2].put("ItemCode", 90);
        values[2].put("ItemDesc", "Headphone");
        values[2].put("Price", 45);

        values[3] = new ContentValues();
        values[3].put("ItemCode", 101);
        values[3].put("ItemDesc", "Keyboard");
        values[3].put("Price", 85);

        for (ContentValues v : values) {
            query.populateData(v);
        }
    }

    void SetUIVariables() {
        one = findViewById(R.id.one);
        two = findViewById(R.id.two);
        three = findViewById(R.id.three);
        four = findViewById(R.id.four);
    }
}