Question

Actually I am developing one application in that when application run
first time it will create one txt file and if file is already exists then it will simply write that on file.
But I don’t know how to check programatically that
file is exist or not.I have tried,

try  
    {  
        FPartyCreation = new File ("/data/data/com.MediExcel/files/","dbPartyCreation.dat");  
        if (FPartyCreation.exists())  
        {  
            writeOnFile();
        }  
        else  
        {  
            FPartyCreation.createNewFile();  
            writeOnFile();
        }  
    }  
    catch (IOException ioe)  
    {  
        ioe.printStackTrace();  
    }  

But it gives following errors , and also file is not created on same path.

07-06 01:39:26.183: E/AndroidRuntime(23107): FATAL EXCEPTION: main
07-06 01:39:26.183: E/AndroidRuntime(23107): java.lang.NullPointerException
07-06 01:39:26.183: E/AndroidRuntime(23107):    at com.MediExcel.AddMethodPartyCreation.getMethod(AddMethodPartyCreation.java:28)
07-06 01:39:26.183: E/AndroidRuntime(23107):    at com.MediExcel.PartyCreationActivity$1.onClick(PartyCreationActivity.java:64)
07-06 01:39:26.183: E/AndroidRuntime(23107):    at android.view.View.performClick(View.java:3511)
07-06 01:39:26.183: E/AndroidRuntime(23107):    at android.view.View$PerformClick.run(View.java:14105)
07-06 01:39:26.183: E/AndroidRuntime(23107):    at android.os.Handler.handleCallback(Handler.java:605)
07-06 01:39:26.183: E/AndroidRuntime(23107):    at android.os.Handler.dispatchMessage(Handler.java:92)
07-06 01:39:26.183: E/AndroidRuntime(23107):    at android.os.Looper.loop(Looper.java:137)
07-06 01:39:26.183: E/AndroidRuntime(23107):    at android.app.ActivityThread.main(ActivityThread.java:4424)
07-06 01:39:26.183: E/AndroidRuntime(23107):    at java.lang.reflect.Method.invokeNative(Native Method)
07-06 01:39:26.183: E/AndroidRuntime(23107):    at java.lang.reflect.Method.invoke(Method.java:511)
07-06 01:39:26.183: E/AndroidRuntime(23107):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
07-06 01:39:26.183: E/AndroidRuntime(23107):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
07-06 01:39:26.183: E/AndroidRuntime(23107):    at dalvik.system.NativeStart.main(Native Method)

Please help me

Thanks

Answer 1

Creating SQLite Database –

public class DatabaseHelper extends SQLiteOpenHelper {

static final String dbName="demoDB";
static final String employeeTable="Employees";
static final String colID="EmployeeID";
static final String colName="EmployeeName";
static final String colAge="Age";
static final String colDept="Dept";

static final String deptTable="Dept";
static final String colDeptID="DeptID";
static final String colDeptName="DeptName";

static final String viewEmps="ViewEmps";

Creating the Database

public void onCreate(SQLiteDatabase db) 
{
    // TODO Auto-generated method stub

    db.execSQL("CREATE TABLE "+deptTable+" ("+colDeptID+ " INTEGER PRIMARY KEY , "+
    colDeptName+ " TEXT)");

  db.execSQL("CREATE TABLE "+employeeTable+" 
    ("+colID+" INTEGER PRIMARY KEY AUTOINCREMENT, "+
        colName+" TEXT, "+colAge+" Integer, "+colDept+" 
    INTEGER NOT NULL ,FOREIGN KEY ("+colDept+") REFERENCES 
    "+deptTable+" ("+colDeptID+"));");


  db.execSQL("CREATE TRIGGER fk_empdept_deptid " +
    " BEFORE INSERT "+
    " ON "+employeeTable+

    " FOR EACH ROW BEGIN"+
    " SELECT CASE WHEN ((SELECT "+colDeptID+" FROM "+deptTable+" 
    WHERE "+colDeptID+"=new."+colDept+" ) IS NULL)"+
    " THEN RAISE (ABORT,'Foreign Key Violation') END;"+
    "  END;");

  db.execSQL("CREATE VIEW "+viewEmps+
    " AS SELECT "+employeeTable+"."+colID+" AS _id,"+
    " "+employeeTable+"."+colName+","+
    " "+employeeTable+"."+colAge+","+
    " "+deptTable+"."+colDeptName+""+
    " FROM "+employeeTable+" JOIN "+deptTable+
    " ON "+employeeTable+"."+colDept+" ="+deptTable+"."+colDeptID
    );
  //Inserts pre-defined departments
  InsertDepts(db);  
 }

Have a look at this Using-SQLite-Database-with-Android blog. Hope this blog is enough for your queries.