What Is a Numberformatexception and How to Fix It

How to fix NumberFormatException?

This answer is not about the number format exception but about the date format mistake you have made.

For the moment, you are parsing 1986-03-01 into the date 1985-12-03 because your String dob contains -. You need two distinct formaters to get your result:

SimpleDateFormat sdfIn = new SimpleDateFormat("yyyy-MM-dd");
SimpleDateFormat sdfOut = new SimpleDateFormat("yyyyMMdd");

String dob = "1985-03-01";
Date dt = sdfIn.parse(dob);
dob = sdfOut.format(dt);

System.out.println(dob);

19850301

Of course, one could argue about the need to parse into a Date just to get a "similar" String, if you are sure about your data being a date, you can just remove - using :

dob = dob.replaceAll("-", "");

Last thing, you should use java.time API.

String dob = "1985-03-01";

LocalDate date = LocalDate.parse(dob, DateTimeFormatter.ofPattern("yyyy-MM-dd"));
dob = date.format(DateTimeFormatter.ofPattern("yyyyMMdd"));

System.out.println(date);
System.out.println(dob);

How can i fix it java.lang.NumberFormatException

The valid range for int is from -0b10000000_00000000_00000000_00000000 to 0b1111111_11111111_11111111_11111111 but the string being parsed is "10000000001000000000101000000001" (one additional bit - the sign bit).

This is valid as an unsigned int, not a primitive type in Java, but it can be parsed using:

Integer.parseUnsignedInt(correct, 2)

(It could also be parsed as a long and converted (cast) to an int)

(there is no unsigned int in Java, all IPs starting with 128 or greater will result in a negative int.)

How to fix NumberFormatException in Java?

Error message seems pretty self explanatory:

java.lang.NumberFormatException: For input string: "4.0"
       at java.lang.Integer.parseInt()

Your string looks like floating point value, not integer.

EDIT

In fact this parsing

centerX = Integer.parseInt(Double.toString(roundedX));

is not needed at all as you can cast double to int directly:

centerX = (int)roundedX;

See type casting

NumberFormatException when trying to use parseInt()and trim() does not fix it

4of is not an integer string and therefore, you can not parse it into an int. You can replace its non-digit characters (\D) with "" and then you can parse it to an int. Learn more about regex patterns from the documentation of java.util.regex.Pattern.

The problem can be solved in the following simple steps:

1. Split the sentence on space (which you have already done).
2. Create an int[] original and populate it with embedded numeric values from the resulting, String[] unordered.
3. Create a clone of original[] and sort the same. Let's say this clone is int[] order.
4. Populate a String[] ordered based on order[].
5. Join the elements of ordered[] on space.

Demo:

import java.util.Arrays;

public class Main {
    public static void main(String[] args) {
        String words = "4of Fo1r pe6ople g3ood th5e the2";
        String[] unordered = words.split(" ");
        String[] ordered = new String[unordered.length];
        int[] original = new int[unordered.length];

        // Populate order with embedded numeric values
        for (int i = 0; i < unordered.length; i++) {
            original[i] = Integer.parseInt(unordered[i].replaceAll("\\D", ""));
        }

        // Create a clone of original[] and sort it
        int[] order = original.clone();
        Arrays.sort(order);

        // Populate ordered[] based on order[]
        for (int i = 0; i < order.length; i++) {
            for (int j = 0; j < original.length; j++) {
                if (order[i] == original[j]) {
                    ordered[i] = unordered[j];
                    break;
                }
            }
        }

        // Join the elements of ordered[] on space
        String result = String.join(" ", ordered);

        System.out.println(result);
    }
}

Output:

Fo1r the2 g3ood 4of th5e pe6ople

How do I fix the error of NumberFormatException everytime I run the program?

NumberFormat is meant to create a human readable string. 70.78% isn't a number. 70.78 is, but with the percent sign, it's a string. It seems like what you're trying to do is use the number formatting functionality to round the number. This question has some suggestions for how to properly round a number and keep it as a number.

To answer your other question, the proper way to use a try/catch would be like this:

 double result;
 try{
   result = Double.parseDouble(nf.format(relationship));
 }catch(NumberFormatException e){
   e.printStackTrace();
   result = 0.0;
 }
 return result;

But the only thing that will do is cause your program to not crash and you'll always get 0.0 returned from the calculate() method. Instead you need to fix the source of the exception.

how to solve Number Format Exception

The problem is Integer.parseInt(binding.a.getText().toString()) and all the subsequent statements eg: binding.b.getText().toString() is empty when the activity onCreate method is called. Integer.parseInt needs a valid number in a string to be able to parse it.

To fix this, check if the value is empty or not, maybe using binding.a.getText().toString().length() != 0. If no, then go ahead and do the parsing.

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