How can I declare dynamic String array in Java

Question

I am using String Array declare as zoom z   new String 422    But this array stores value from 0 to 32  so I got null pointer exception after looping value 32    How to solve this problem in java   How can I declare a dynamic array in java

User · Answer

no  there is no way to make array length dynamic in java   you can use ArrayList or other List implementations instead

User · Answer

The Array newInstance Class lt   gt  componentType  int length  method is to be used to create an array with dynamically length   Multi-dimensional arrays can be created similarly with the Array newInstance Class lt   gt  componentType  int    dimensions  method

User · Answer

What your looking for is the DefaultListModel - Dynamic String List Variable   Here is a whole class that uses the DefaultListModel as though it were the TStringList of Delphi   The difference is that you can add Strings to the list without limitation and you have the same ability at getting a single entry by specifying the entry int   FileName  StringList java  package YOUR PACKAGE GOES HERE     This is the StringList Class by i2programmer   You may delete these comments   This code is offered freely at no requirements   You may alter the code as you wish import java io File  import java io FileReader  import java io FileWriter  import java io IOException  import java util logging Level  import java util logging Logger  import javax swing DefaultListModel   public class StringList        public static String OutputAsString DefaultListModel list  int entry            return GetEntry list  entry              public static Object OutputAsObject DefaultListModel list  int entry            return GetEntry list  entry              public static int OutputAsInteger DefaultListModel list  int entry            return Integer parseInt list getElementAt entry  toString                public static double OutputAsDouble DefaultListModel list  int entry            return Double parseDouble list getElementAt entry  toString                public static byte OutputAsByte DefaultListModel list  int entry            return Byte parseByte list getElementAt entry  toString                public static char OutputAsCharacter DefaultListModel list  int entry            return list getElementAt entry  toString   charAt 0              public static String GetEntry DefaultListModel list  int entry            String result               result   list getElementAt entry  toString            return result             public static void AddEntry DefaultListModel list  String entry            list addElement entry              public static void RemoveEntry DefaultListModel list  int entry            list removeElementAt entry              public static DefaultListModel StrToList String input  String delimiter            DefaultListModel dlmtemp   new DefaultListModel            input   input trim            delimiter   delimiter trim            while  input toLowerCase   contains delimiter toLowerCase                   int index   input toLowerCase   indexOf delimiter toLowerCase                 dlmtemp addElement input substring 0  index  trim                 input   input substring index   delimiter length    input length    trim                      return dlmtemp             public static String ListToStr DefaultListModel list  String delimiter            String result               for  int i   0  i  lt  list size    i                  result   list getElementAt i  toString     delimiter                    result   result trim            return result             public static String LoadFile String inputfile  throws IOException           int len          char   chr   new char 4096           final StringBuffer buffer   new StringBuffer            final FileReader reader   new FileReader new File inputfile            try               while   len   reader read chr    gt  0                    buffer append chr  0  len                           finally               reader close                      return buffer toString               public static void SaveFile String outputfile  String outputstring            try               FileWriter f0   new FileWriter new File outputfile                f0 write outputstring               f0 flush                f0 close              catch  IOException ex                Logger getLogger StringList class getName    log Level SEVERE  null  ex                       OutputAs methods are for outputting an entry as int  double  etc    so that you don t have to convert from string on the other side   SaveFile  amp  LoadFile are to save and load strings to and from files   StrToList  amp  ListToStr are to place delimiters between each entry   ex  1 lt  2 lt  3 lt  4 lt   if   lt    is the delimiter and 1 2 3  amp  4 are the entries   AddEntry  amp  GetEntry are to add and get strings to and from the DefaultListModel   RemoveEntry is to delete a string from the DefaultListModel   You use the DefaultListModel instead of an array here like this   DefaultListModel list   new DefaultListModel      now that you have a list  you can run it through the above class methods

User · Answer

You want to use a Set or List implementation  e g  HashSet  TreeSet  etc  or ArrayList  LinkedList  etc     since Java does not have dynamically sized arrays   List lt String gt  zoom   new ArrayList lt  gt     zoom add  String 1    zoom add  String 2     for  String z   zoom        System err println z       Edit  Here is a more succinct way to initialize your List with an arbitrary number of values using varargs   List lt String gt  zoom   Arrays asList  String 1    String 2    String n

User · Answer

Maybe you are looking for Vector  It s capacity is automatically expanded if needed   It s not the best choice but will do in simple situations  It s worth your time to read up on ArrayList instead

[java] How can I declare dynamic String array in Java

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