Android Day of Week Calculator

Pavlex4

I have created program that calculates day of week when entered date in format "January 7 2000" .Why do I get NullPointerException exception when I click button to calculate day of week? Here is source code of app:

public class MainActivity extends AppCompatActivity
{
private int position;
private int value;
private Button button;
private EditText editText;
private TextView textView1,textView2;
private Spinner spinner,spinner2;
private ArrayAdapter adapter;

private boolean isValid;
private Date date;
private int inMonth, inDay, inYear;

static boolean isDateValid(int month, int day, int year)
{
    boolean validation = true;
    int\[\] daysInMonth = { 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 };

    if (month < 1 || month > 12)
    {
        validation = false;
    }

    if (day < 1 || day > daysInMonth\[month - 1\])
    {
        validation = false;
    }

    if (year < 1700 || year > 3000)
    {
        validation = false;
    }
    return validation;
}

static String zellerCalc(int month, int day, int year)
{
    String dayOfWeek;
    int m = -1; 
    int h = -1; 
    int q = day;
    int k;
    int j;

    if (month == 1)
    {
        m = 13;
    }
    else if (month == 2)
    {
        m = 14;
    }
    else
    {
        m = month;
    }

    if (m == 13 || m == 14)
    {
        year--;
    }

    k = year % 100;
    j = year / 100; 

    h = (q + (int)((13 \* (m + 1)) / 5.0) + k + (int)(k / 4.0) + (int)(j / 4.0) + (5 \* j)) % 7;

    if (h == 0)
    {
        dayOfWeek = "Subota";
    }
    else if (h == 1)
    {
        dayOfWeek = "Nedelja";
    }
    else if (h == 2)
    {
        dayOfWeek = "Ponedeljak";
    }
    else if (h == 3)
    {
        dayOfWeek = "Utorak";
    }
    else if (h == 4)
    {
        dayOfWeek = "Sreda";
    }
    else if (h == 5)
    {
        dayOfWeek = "Četvrtak";
    }
    else
        dayOfWeek = "Petak";

    return dayOfWeek;
}

@Override
protected void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity\_main);
    Too

David Crow

Seriously? A NullPointerException is being thrown on line 230 because date is null. A simple walkthrough with the debugger would have revealed this. :doh:

"One man's wage rise is another man's price increase." - Harold Wilson

"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons

"You can easily judge the character of a man by how he treats those who can do nothing for him." - James D. Miles

Pavlex4

I have initialized Date date = new Date(); but now I get application has stopped working and error is still in the same line!!!

try
{
Date date = new Date();
String getdate = spinner.getItemAtPosition(position).toString() + value
+ textView2.getText().toString();
date = sdf.parse(getdate);
} catch (ParseException ex)
{
// handle parsing exception if date string was different from the pattern applying into the SimpleDateFormat contructor
}
// isDateValid function call
isValid = isDateValid(date.getMonth(), date.getDay(), date.getYear());

David Crow

Pavlex4 wrote:

I have initialized Date date = new Date();

Which is not the one being passed to isDateValid().

"One man's wage rise is another man's price increase." - Harold Wilson

"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons

"You can easily judge the character of a man by how he treats those who can do nothing for him." - James D. Miles

Pavlex4

So,what should I do?

David Crow

Maybe look at (or around) line 12.

"One man's wage rise is another man's price increase." - Harold Wilson

"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons

"You can easily judge the character of a man by how he treats those who can do nothing for him." - James D. Miles

Pavlex4

You mean this "private Date date;" ?

David Crow

Correct.

"One man's wage rise is another man's price increase." - Harold Wilson

"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons

"You can easily judge the character of a man by how he treats those who can do nothing for him." - James D. Miles

Pavlex4

What is problem with that line?

Lost User

Nothing.

Pavlex4

I added date = new Date(); to button onclicklistener but when I click button inside app it gets pressed and stays like that and nothing happens!!!

button.setOnClickListener(new View.OnClickListener()
{
@Override
public void onClick(View view)
{
String dayOfWeek;
boolean isValid;

            **date = new Date();**

            Calendar c = Calendar.getInstance();
            SimpleDateFormat sdf = new SimpleDateFormat("yyyyMMdd\_HHmmss");
            String strDate = sdf.format(c.getTime());

Lost User

You really need to make more effort to do some debugging of your code first. You have a problem which could be caused by any part of your code, so you need to do the troubleshooting to collect more information. Also you have a try/catch block in your code that reads:

        try
            {
                String getdate = spinner.getItemAtPosition(position).toString() + value
                        + textView2.getText().toString();
                Date date = sdf.parse(getdate);
            }
            catch (ParseException ex)
            {

            }

Do not do this, you are just hiding any problems that may occur. Put some proper code in the catch block to help you find errors.

David Crow

Can you not see that you have two Date objects (in separate scopes)?

"One man's wage rise is another man's price increase." - Harold Wilson

"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons

"You can easily judge the character of a man by how he treats those who can do nothing for him." - James D. Miles

Lost User

Why check your own code when you can get it done for free at CodeProject? ;P