Android math operator - android

I need calculate a thing. but my formula sentence has occur some problem.
TextView ticketP = (TextView)findViewById (R.id.ticketQ);
ticketP.setText(oneSession.getTicketOder());
String Ctotal = "";
Ctotal = jsonObject.optString("price");
String OneTotal = oneSession.getTicketOder() * Ctotal; // this part has occur the problem which is the operator * .

You'll need to convert the Strings to numeric type before performing any multiplication. Depending on the type of numeric value you are using take a look Double.parseDouble(String string) or Integer.parseInt(String string).

int oneTotal = Integer.valueOf(oneSession.getTicketOder()) * Integer.valueOf(Ctotal);
to convert it again to String use
String.valueOf(oneTotal)

Yes. Your going to have to use the parsing methods in order to convert the string to a native numerical type. You also need to be care about a few things with your code.
json.optString() can return null. opt = optional.
I would suggest using json.getInt() or json.getDouble() this will not only give you the correct type, but also throw an exception if the values aren't correct.
Secondly your going to have to convert your numerical answer back to a string if you want to display it. But this is easy enough with a .toString() or + "" if you are lazy.

Related

How can i show the value before the "." sign?

I'm creating a currency application but some of values are like "194.23564" or "1187.7594" so i want to show the user before the "." sign values. How can i make this with Kotlin ?
There is no need for data type conversion before the extraction of the integer part.
You can use substringBefore():
val number = "194.23564"
val intPart = number.substringBefore(".")
If you want the result as an integer number you can use now toIntOrNull(), instead of toInt(), so to avoid an exception in case the initial string has no integer part (like ".015"):
val intPart = number.substringBefore(".").toIntOrNull()
Other than suggested, I would not convert to Float. This is susceptible to rounding errors and may not return the value before the decimal point.
Example:
val num = "0.99999999"
println(num.toFloat().toInt()) // gives 1
Instead, split the string at the decimal point:
val num = "0.99999999"
val split = num.split('.')
println(split[0]) // gives 0
A nice side effect of this implementation is that it even works for integral numbers without a decimal point. If you need the result as an Int, simply call split[0].toInt().
There is no need to use float in this case. If you want to get the value before ".", you need to use int instead of float. When you use float you will get value in points, but when you use int, you will get the value before ","

How to parse a String which is a multidimensional array representaion

I'm now working on Java on Android platform and facing problem extracting the strings out of a string as followings
result.toString();
The toString is expected to return the results as following:
[ search[name = Tulsa, code = 1234], search[name = Victo, code = 1232] ]
Then, may I know what is the best and the efficient way to store the results returned into arrays like followings:
array[0][0] = "Tulsa";
array[0][1] = 1234;
array[1][0] = "Victo";
array[1][1] = 1232;
or is there any more efficient, better way available for storing?
Well you can use result.toString().split(",") which will return you a String array. But it seems that not your case.
P.S. Could you specify what the "code" in toString method is?
P.S. I think the most efficient way is to use Map. In that case you could just use
map.put("Tulsa",1234)
map.put("Victo",1234)
etc

Minusing string number values in android

I am making an android application where i got a set of strings that i load from SharedPreferences so that i can save the strings. The strings contain only numbers, but it is not an int value, its a string value. And i wounder how i can minus the numbers that's in there, becuase usually, i would have been using something like an int value = value - value; But that doesn't seem to work since it's a string and not an int value. How can i do this even though it's a string? I know i could use int values instead, but as i didn't think of this before now, when i'm almost done, it would be alot of work changing all of the code that's related to this. Please help me and thanks so much in advance!
You will have to convert your strings to ints first, then operate on them, then save the string back:
String value = preferences.getString("key:");
int intValue = Integer.valueOf(value);
intValue = intValue - 1;
preferences.edit().putString("key", Integer.toString(intValue)).commit();
Try using Integer.valueOf(string) or Integer.parseInt(string).
Learning basic programming the the concept of casting will help you tremendously. One datatype can be converted to another using the base classes, which often times deal with String. For instance look at the Documentation of Integer.
Well as you have said that it is a lot of work to change the code and save it as int, I would suggest converting the string into an integer, refer to this link for more information, someone has asked about converting strings to integers, and as Android is Java-based, this can apply to your project:
Converting a string to an integer on Android
Hope this helps.

Android SDK. String index out of bound exception

I FINALLY have the map and points(arrays) working for my app. Quick question: I have a fatal exception with substring(), a "stringIndexOutOfBoundException"
In general, what is that referring to?
An I going past the end of a string using substring()?
Thanks,
testing.substring(1,2);
(I want to parse each character to find specific characters)
I wouldn't use substring() for grabbing 1-length strings (which is just a single character), but rather charAt(int) for specific positions. If you need to go over all characters in the string, you're probably better off with by converting the whole thing to a char[] first (using toCharArray()) and iterate over that.
Yes, you're going past the end of your strings bounds generally.
The Java API even tells you so...
IndexOutOfBoundsException - if beginIndex is negative or larger than the length of this String object.
You should get used to using the API. It tells you what exceptions a method throws and why.
Try printing the Strings length and value before attempting substring. That'll help you see the problem.
For example...
String testing = "Hello StackOverflow";
System.out.println("Length of testing = " + testing.length);
System.out.println("Value of testing = " + testing);
testing.substring(1,2);
Like stated in the official doc here:
public String substring(int beginIndex)
Returns a new string that is a substring of this string. The substring begins with the character at the specified index and extends to the end of this string.
Throws: IndexOutOfBoundsException - if beginIndex is negative or
larger than the length of this String object.

Why does this trigger a force close on Android?

Why does this code trigger a force close in Android?
`score.setText(Integer.parseInt((String) score.getText())+1);`
score is a TextView, and I am simply increasing the number by 1. I have predefined a String resource to be the initial number in the score TextView.
I am quite frustrated.
First off you should try breaking down your code so you can actually see what is going on with it.
Instead of
score.setText(Integer.parseInt((String) score.getText())+1);
try
String tmp = score.getText().toString();
int score;
score = Integer.parseInt(tmp) + 1;
score.setText(String.valueOf(score));
EDIT: Upon further reading of the documentation, setText has several overloads, one of which DOES take an int, but it takes the int of a resource ID. My guess is that your score is not a valid resource ID, thus crashing your application.
public final void setText (int resid)
Oh and as far as the frequent FC's when beginning Android Dev, it happens to the best of us. The key is to learn WHY the FC's happen, and have a LOT of patience.
mostly u need to do this
score.setText(Integer.parseInt(score.getText().toString())+1);
coz.. getText() returns a Editable Object which cannot be parsed to Integer. So it give NumberFormat Exception.
AndMake sure to set TextView,s Text to an integer initially..
try this way
score.setText(String.valueOf(Integer.parseInt(score.getText().toString())+1));
as you can pass the integer value that's why getting force the application
TextEdit.setText takes a CharSequence as input.
You are supplying an integer through Integer.parseInt((String) score.getText())+1
See, if converting it back to string and using it in setText helps.
You can convert an integer to string using Integer.toString.
PS: I am new to java myself.
The compiler should have ideally caught this error.
It's possible java uses some implicit type conversions from string to int.

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