Java ArrayList of Arrays

Question

I want to create a mutli dimensional array without a fixed size   I need to be able to add items of String 2  to it   I have tried looking at   private ArrayList lt String   gt  action   new ArrayList lt String 2  gt       but that doesn t work   does anyone have any other ideas

User · Answer

Since the size of your string array is fixed at compile time, you'd be better off using a structure (like Pair) that mandates exactly two fields, and thus avoid the runtime errors possible with the array approach.

Code:

Since Java doesn't supply a Pair class, you'll need to define your own.

class Pair<A, B> {
  public final A first;
  public final B second;

  public Pair(final A first, final B second) {
    this.first = first;
    this.second = second;
  }

  //
  // Override 'equals', 'hashcode' and 'toString'
  //
}

and then use it as:

List<Pair<String, String>> action = new ArrayList<Pair<String, String>>();

[ Here I used List because it's considered a good practice to program to interfaces. ]

User · Answer

As already answered  you can create an ArrayList of String Arrays as  P  ter T  r  k written         Declaration of an ArrayList of String Arrays     ArrayList lt String   gt  listOfArrayList   new ArrayList lt String   gt       When assigning different String Arrays to this ArrayList  each String Array s length will be different   In the following example  4 different Array of String added  their lengths are varying   String Array  1  len  3 String Array  2  len  1 String Array  3  len  4 String Array  4  len  2   The Demonstration code is as below   import java util ArrayList   public class TestMultiArray        public static void main String   args              Declaration of an ArrayList of String Arrays         ArrayList lt String   gt  listOfArrayList   new ArrayList lt String   gt                Assignment of 4 different String Arrays with different lengths         listOfArrayList add  new String    line1  test String 1   line1  test String 2   line1  test String 3               listOfArrayList add  new String    line2  test String 1               listOfArrayList add  new String    line3  test String 1   line3  test String 2   line3  test String 3    line3  test String 4               listOfArrayList add  new String    line4  test String 1   line4  test String 2                   Printing out the ArrayList Contents of String Arrays                is used to indicate the String elements of String Arrays         for  int i   0  i  lt  listOfArrayList size    i                   for  int j   0  j  lt  listOfArrayList get i  length  j                     System out printf         listOfArrayList get i  j                 System out println                         And the output is as follows      line1  test String 1   line1  test String 2   line1  test String 3    line2  test String 1    line3  test String 1   line3  test String 2   line3  test String 3   line3  test String 4    line4  test String 1   line4  test String 2   Also notify that you can initialize a new Array of Sting as below   new String    str1  str2  str3           Assuming str s are String objects   So this is same with   String   newStringArray     str1  str2  str3       Assuming str s are String objects   I ve written this demonstration just to show that no theArrayList object  all the elements are references to different instantiations of String Arrays  thus the length of each String Arrays are not have to be the same  neither it is important   One last note  It will be best practice to use the ArrayList within a List interface  instead of which that you ve used in your question   It will be better to use the List interface as below         Declaration of an ArrayList of String Arrays     List lt String   gt  listOfArrayList   new ArrayList lt String   gt

User · Answer

Should be  private ArrayList lt String   gt  action   new ArrayList lt String   gt     action add new String 2          You can t specify the size of the array within the generic parameter  only add arrays of specific size to the list later  This also means that the compiler can t guarantee that all sub-arrays be of the same size  it must be ensured by you   A better solution might be to encapsulate this within a class  where you can ensure the uniform size of the arrays as a type invariant

User · Answer

This works very well   ArrayList lt String   gt  a   new ArrayList lt String   gt         a add new String 3        a get 0  0     Zubair       a get 0  1     Borkala       a get 0  2     Kerala   System out println a get 0  1      Result will be  Borkala

User · Answer

ArrayList lt String   gt  action   new ArrayList lt String   gt       Don t need String 2

User · Answer

BTW  you should prefer coding against an Interface   private ArrayList lt String   gt  action   new ArrayList lt String   gt       Should be  private List lt String   gt  action   new ArrayList lt String   gt

User · Answer

Create the ArrayList like ArrayList action   In JDK 1 5 or higher use ArrayList  lt string   gt  reference name   In JDK 1 4 or lower use ArrayList reference name  Specify the access specifiers    public  can be accessed anywhere private  accessed within the class protected  accessed within the class and different package subclasses  Then specify the reference it will be assigned in  action   new ArrayList lt String   gt      In JVM new keyword will allocate memory in runtime for the object   You should not assigned the value where declared  because you are asking without fixed size  Finally you can be use the add   method in ArrayList  Use like  action add new string how much you need     It will allocate the specific memory area in heap

[java] Java ArrayList of Arrays?

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