Update Existing Table

UpgradeTable.java

public void upgradeTable(SQLiteDatabase db) {
        MyTableHandler mth = new MyTableHandler();
        mth.createTable(db);

        ArrayList<String> columns = getColumns(db, TABLE_NAME);
        String alterQuery = "ALTER TABLE " + TABLE_NAME + " RENAME TO temp_" + TABLE_NAME;
        db.execSQL(alterQuery);

        mth.createTable(db);
        columns.retainAll(DatabaseHandler.getColumns(db, TABLE_NAME));
        String cols = join(columns, ",");
        db.execSQL(String.format("INSERT INTO %s (%s) SELECT %s FROM temp_%s",
                TABLE_NAME, cols, cols, TABLE_NAME));
        String dropQuery = "DROP TABLE temp_" + TABLE_NAME;
        db.execSQL(dropQuery);
    }


public ArrayList<String> getColumns(SQLiteDatabase db, String tableName) {
        ArrayList<String> al = null;
        Cursor c = null;
        try {
            c = db.rawQuery("SELECT * FROM " + tableName + " LIMIT 1", null);
            if (c != null) {
                al = new ArrayList<>(Arrays.asList(c.getColumnNames()));
            }
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            if (c != null)
                c.close();
        }
        return al;
    }

public String join(ArrayList<String> al, String delim) {
        StringBuilder sb = new StringBuilder();
        int num = al.size();
        for (int i = 0; i < num; i++) {
            if (i != 0)
                sb.append(delim);
            sb.append(al.get(i));
        }
        return sb.toString();
    }