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Thread: Conversion of string into integer in Java

  1. #1
    mmm.. coffee JavaPF's Avatar
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    Default Conversion of string into integer in Java

    public static void main(String[] args) {
     
    String yourString = "420";
    int yourInt = Integer.parseInt(yourString);
     
    System.out.println(yourInt);
    }
    Please use [highlight=Java] code [/highlight] tags when posting your code.
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    Default Re: How to convert String to int

    Dude you just help me big time now i can finish like 7 programs!

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    Administrator copeg's Avatar
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    Default Re: How to convert String to int

    If you are unsure of the input, make sure to catch any NumberFormatExceptions that can be thrown when trying to parse something that can't be parsed
    public static void main(String[] args) {
         int yourInt = -1;
        if ( args.length > 0 ){     
            try{
                yourInt = Integer.parseInt(args[0]);
            }catch ( NumberFormatException e ){
                System.out.println("Wrong number...");
                return;
            }
        }else{
            System.out.println("No input....");
            return;
        }
        System.out.println(yourInt);
    }
    Last edited by copeg; October 25th, 2009 at 10:24 PM.

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    Super Moderator Json's Avatar
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    Default Re: How to convert String to int

    Personally I'd check the input before trying to parse it as exceptions are slow.

    // Json

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    Administrator copeg's Avatar
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    Default Re: How to convert String to int

    Quote Originally Posted by Json View Post
    Personally I'd check the input before trying to parse it as exceptions are slow.

    // Json
    Good point. Out of curiosity though...according to this benchmark below going through the try/catch block is 10 times faster than validation (with correct input of course). For incorrect input the validation is 2 times faster than try/catch. I know in the real world things are much different, and there are probably other ways that are potentially faster to do validation, but its just food for thought.

    public class ExceptionTest{
     
    	public static void main( String[] args ){
    		String input = "126";
    		long start = System.currentTimeMillis();
     
    		for ( int i = 0 ; i < 100000; i++ ){
    			try{
    				int st = Integer.parseInt(input);
    			}catch ( NumberFormatException e ){
    				//System.out.println("Error");
    			}
    		}
     
    		System.out.println(System.currentTimeMillis() - start );
    		start = System.currentTimeMillis();
    		for ( int i = 0 ; i < 100000; i++ ){
    			if ( !input.matches("[0-9]+") ){
    				//System.out.println("Error");
    			}else{
                                   int st = Integer.parseInt(input);
                            }
     
    		}
    		System.out.println(System.currentTimeMillis() - start );
    	}
    }
    Last edited by copeg; October 26th, 2009 at 01:45 PM.

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    Super Moderator Json's Avatar
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    Default Re: How to convert String to int

    I updated your code somewhat to add an input checker of my own.

    package uk.co.cdl.testing.io;
     
    public class ExceptionTest1 {
        public static void main(String[] args) {
            String input = "126h";
            long start = System.currentTimeMillis();
     
            for (int i = 0; i < 100000; i++) {
                try {
                    int st = Integer.parseInt(input);
                } catch (NumberFormatException e) {
                    //System.out.println("Error");
                }
            }
     
            System.out.println("Exceptions: " + (System.currentTimeMillis() - start) + "ms");
            start = System.currentTimeMillis();
            for (int i = 0; i < 100000; i++) {
                if (!input.matches("[0-9]+")) {
                    //System.out.println("Error");
                } else {
                    int st = Integer.parseInt(input);
                }
     
            }
            System.out.println("Regexp: " + (System.currentTimeMillis() - start) + "ms");
     
     
            start = System.currentTimeMillis();
            for (int i = 0; i < 100000; i++) {
                if (isDigits(input)) {
                    int st = Integer.parseInt(input);
                }
            }
            System.out.println("isDigits: " + (System.currentTimeMillis() - start) + "ms");
        }
     
        public static boolean isDigits(final String input) {
            if (input == null) {
                return false;
            } else if ("".equals(input)) {
                return false;
            } else {
                for (int i = 0; i < input.length(); ++i) {
                    if (!Character.isDigit(input.charAt(i))) {
                        return false;
                    }
                }
            }
     
            return true;
        }
    }

    In the case where the input is not a number I get the following output.

    Exceptions: 203ms
    Regexp: 141ms
    isDigits: 0ms
    And in the case were the input is a number I get the following output.

    Exceptions: 0ms
    Regexp: 141ms
    isDigits: 0ms
    // Json

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    copeg (October 27th, 2009)

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    Default Re: How to convert String to int

    Thanks for posting that code Json.

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    Default Re: How to convert String to int

    when i tried this code

    String yourString = "Ashar";
    int yourInt = Integer.parseInt(yourString);
     
    System.out.println(yourInt);

    it compiled showing no errors ... however when I run the program i get an exception in thread "main" java.lang.NumberFormatException: for input String "Ashar" along with other things on the console after running the program

    I want to know why that happens ... I thought this statement will give me the ASCII equivalent to the string "Ashar"

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    Default Re: How to convert String to int

    Quote Originally Posted by Ashar View Post
    when i tried this code

    String yourString = "Ashar";
    int yourInt = Integer.parseInt(yourString);
     
    System.out.println(yourInt);

    it compiled showing no errors ... however when I run the program i get an exception in thread "main" java.lang.NumberFormatException: for input String "Ashar" along with other things on the console after running the program

    I want to know why that happens ... I thought this statement will give me the ASCII equivalent to the string "Ashar"
    No this is designed for converting a String representation of a Numerical value into a numerical value.

    I.e "1" would become integer 1 and "8" would become integer 8 rather than string literals.

    the following would print each of the ascii values.

    public void printAscii(String s){
       for(int i = s.length-1; i > -1; i--)
          System.out.print((int)s.charAt(i));
       System.out.println();
    }

    Chris
    Last edited by Freaky Chris; December 4th, 2009 at 08:27 AM.
    chris[at]javaprogrammingforums[dot]com

    Prifysgol Bangor University, North Wales

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    Ashar (December 4th, 2009)

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    Default Re: How to convert String to int

    Thank you chris

    can you tell me why was it used in a program to read a number .. does JOptioPane always reads strings?
    like this :
     int x = Integer parseInt(JOprionPane.showInputDialog("Enter number") ;

  13. #11
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    Default Re: How to convert String to int

    JOptionPane.showInputDialog() does indeed always return a String
    chris[at]javaprogrammingforums[dot]com

    Prifysgol Bangor University, North Wales

  14. #12
    Super Moderator Json's Avatar
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    Default Re: How to convert String to int

    Or null?

    // Json

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    Default Re: How to convert String to int

    Well yes or null i suppose, but its a null String lol
    chris[at]javaprogrammingforums[dot]com

    Prifysgol Bangor University, North Wales

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    Super Moderator Json's Avatar
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    Default Re: How to convert String to int

    hehe

    // Json

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    Question Re: How to convert String to int

    Hi guys, I don't understand a thing...
    Let me give you some code first:

    public class Airplane {
     
    	private String plane, firstLetter, lastLetter;
    	private int nRows;
    	private int columns;
    	String[] windowsSeats;
    	String[] aisleSeats;
     
     
     
    	public Airplane(String plane, int nRows, String firstLetter, String lastLetter) {
    		this.plane=plane;
    		this.nRows=nRows;
    		this.firstLetter=firstLetter;
    		this.lastLetter=lastLetter;
     
     
    		try{
    			this.columns=Integer.parseInt(lastLetter)-Integer.parseInt(firstLetter)+1;
            }catch ( NumberFormatException e ){
                System.out.println("Wrong number...");
                return;
            }
    ...
     
    	}

    I throw it with a kind of main like:

    public class MainExample {
     
     
    	public static void main(String[] args) throws FullFlight, SeatTaken, NoPlane, NoSeat {
     
     
    		FlightManager  fm = new FlightManager();
    		fm.addAirplane("B737-1", 32, "A", "F");
    		fm.addAirplane("B737-2", 42, "A", "F");
     
    		...
    }

    I obtain always the error message.. Can you explain why the conversion (this.columns..) doesn't succeed?

  18. #16
    Super Moderator Json's Avatar
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    Default Re: How to convert String to int

    Hello there, its because you are trying to find a numeric value in a string which is the letter "F" or "A", this will always throw a NumberFormatException because neither A or F are numbers.

    If you wish to convert this into their ASCII equivalents you can use this.

    Character.getNumericValue(lastLetter);

    You also need to make sure that lastLetter and firstLetter is a char instead of a String.

    Hope that helps.

    // Json

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    Cool Re: How to convert String to int

    Hi Json and thanks for the answer first!
    I understood your thesis but unfortunately I can not change the type of firstLetter and lastLetter. they're passed as String in the function.

    Can I find another way to solve it?
    Take into account that it is a Flight Manager program, the function "addAirplane" receives these 2 String as parameters, and I must be able to, when I make a reservation, understand how many "columns" of seats there are and also for compute the capacity of an airplane (rows*columns).

    I accept any kind of explanation and help.
    Is very important to me to understand because it is part of an exam at univerisity.

    Thanks

  20. #18
    Super Moderator Json's Avatar
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    Default Re: How to convert String to int

    If you know that the 2 strings are always going to be 1 character long you can do this.

    char character = firstLetter.charAt(0);

    That will grab the character at the first position in the string and then you can use that to get the int value.

    // Json

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    Daddo (January 23rd, 2010)

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