Exception in thread main java lang ArrayIndexOutOfBoundsException

Question

I am a beginner to programming  I m a few weeks into my first programming class  so please bear with me  I am not a person to ask for help  so I have searched for an answer extensively with no luck  This is also my first time posting anything in any type of forum  so if my question structure is off I m sorry and I will correct for future posts   This is the question I am tackling      Write a program that declares an array  alpha  of 50 elements of type  double    Initialize the array so that the first 25 elements are equal to the square of the index variable and the last 25 elements are equal to three times the index variable  Output the array so that 10 elements per line are printed    This is what I got while running the program   Exception in thread  main  java lang ArrayIndexOutOfBoundsException 50 on line 23    And this is the code I m working on   import java util    import java lang    public class ProgrammingProblem5 4       public static void main String   args                 int i 0          int count 0          double   alpha   new double 50             if  i  gt   25              alpha i    3 i          System out print alpha i                    count            if  count  10                System out println   n                count 0                        Thank you in advance for any help  I m not looking to have this done for me  I m just stuck and need help finding my way

User · Answer

First you should learn about loops  in this case most suitable is for loop  For instance let s initialize whole table with increasing values starting with 0   final int SIZE   10  int   array   new int SIZE   for  int i   0  i  lt  SIZE  i          array i    i      Now you can modify it to initialize your table with values as per your assignment  But what happen if you replace condition i  lt  SIZE with i  lt  11  Well  you will get IndexOutOfBoundException  as you try to access  at some point  an object under index 10  but the highest index in 10-element array is 9  So you are trying  in other words  to find friend s home with number 11  but there are only 10 houses in the street   In case of the code you presented  well  there must be more of it  as you can not get this error  exception  from that code

User · Answer

ArrayIndexOutOfBoundsException in simple words is -  you have 10 students in your class  int array size 10  and you want to view the value of the 11th student  a student who does not exist   if you make this int i 3  then i takes values i 0  i 1  i 2   for your problem try this code structure   double   array   new double 50        for  int i   0  i  lt  24  i                  for  int j   25  j  lt  50  j

User · Answer

i don t see any for loop to initalize the variables you can do something like this   for i 0 i lt 50 i         Code which is necessary with a simple if statement

User · Answer

I still remember the first weeks of my programming courses and I totally understand how you feel  Here is the code that solves your problem  In order to learn from this answer  try to run it adding several  print  in the loop  so you can see the progress of the variables    import java util    import java lang     public class foo       public static void main String   args              double   alpha   new double 50         int count   0         for  int i 0  i lt 50  i                         System out print  variable i       i     n              if  i  lt  25                              alpha i    i i                        else                   alpha i    3 i                         if  count  lt  10                          System out print alpha i                                  else               System out print   n                 System out print alpha i                      count   0                         count                   System out print   n

[java] Exception in thread "main" java.lang.ArrayIndexOutOfBoundsException

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