Iterate through string array in Java

Question

I have String array with some components  this array has 5 components and it vary some times  What I would like to do is to iterate through that array and get the first component and the component next to that one  So the first time I would get the component number one and the component number 2  the second time would get the number 2 and 3  the third time number 3 and 4    And so on until you get to the last component    This how far I have come    String   elements      a    a   a   a      for  int i   0  i  lt   elements length - 1  i             get element number 0 and 1 and put it in a variable          and the next time get element      1 and 2 and put this in another variable       How can I accomplish this

User · Answer

I would argue instead of testing i less than  elements length - 1  testing i   1 less than elements length  You aren t changing the domain of the array that you are looking at  i e  ignoring the last element   but rather changing the greatest element you are looking at in each iteration   String   elements      a    a   a   a      for int i   0  i   1  lt  elements length  i          String first   elements i       String second   elements i 1         do something with the two strings

User · Answer

As long as this question remains unsanswered the OP s problem and Java has evolved over the years  I have decided to put my own one  Let s change for sake of clarity the input String array to have 5 unique items  String   elements     quot a quot    quot b quot    quot c quot    quot d quot    quot e quot     You want to access two siblings in the list with each iteration incremented by one index  for  int i 0  i lt elements length-1  i                note the condition     String left   elements i       String right   elements i 1        System out println left    quot   quot    right           prints 4 lines    Printing the pairs of left and right in four iterations result in the lines a b  b c  c d  d e in your console  What can happen if the input string array has less than 2 elements  Nothing prints our as long as this for-loop extracts always two sibling nodes  With less than 2 elements the program doesn t enter to the loop itself  As far as your snippet says you want to not discard the extracted values but add them an another  variable  assuming outside the scope of the for-loop  you want  to store them in either a list or an array  Let s say you want to concatenate the siblings with the   character  List lt String gt  list   new ArrayList lt  gt     String   array   new String elements length-1       note the defined size  for  int i 0  i lt elements length-1  i          String left   elements i       String right   elements i 1        list add left    quot   quot    right                 adds to the list     array i    left    quot   quot    right               adds to the array    Printing the contents both of the list and the array  Arrays toString array   results in   a b  b c  c d  d e   Java 8 As of Java 8  you might be tempted to use the advantage of Stream API  however  it was made for procesing the individual elements from a source collection  There is no such method for processing 2 or more sibling nodes at once  The only way is to use Stream API to process the indices instead and map them to the real value  As long as you start with a primitive Stream called IntStream you need to use IntStream  mapToObj method to get boxed Stream lt T gt   String   array   IntStream range 0  elements length-1       mapToObj i - gt  elements i     quot   quot    elements i   1        toArray String    new                                    a b  b c  c d  d e   List lt String gt  list   IntStream range 0  elements length-1       mapToObj i - gt  elements i     quot   quot    elements i   1        collect Collectors toList                                a b  b c  c d  d e

User · Answer

String current   elements i   if  i    elements length - 1       String next   elements i 1       This makes sure you don t get an ArrayIndexOutOfBoundsException for the last element  there is no  next  there   The other option is to iterate to i  lt  elements length - 1  It depends on your requirements

User · Answer

If you are looking for performance and the order of iteration is not relevant  you can iterate using an optimized reverse loop  int elemLength   elements length  if elemLength  lt  2        avoid ArrayIndexOutOfBoundsException       else     String elem1  elem2    for int i   elemLength -1  --i  gt   0         elem1   elements i       elem2   elements i 1          do whatever you want with those two strings        In such a way you are retrieving the length of the array once  then decrementing the index and comparing with zero in a single operation  Comparing with zero is a very fast operation  often optimized by many architectures  easier   faster than comparing to the length of the array

User · Answer

You have to maintain the serial how many times you are accessing the array Use like this  int lookUpTime 0       for int i lookUpTime i lt lookUpTime 2  amp  amp  i lt elements length   i                  do something with elements i         lookUpTime

User · Answer

Those algorithms are both incorrect because of the comparison   for  int i   0  i  lt  elements length - 1  i     or  for int i   0  i   1  lt  elements length  i       It s true that the array elements range from 0 to length - 1  but the comparison in that case should be less than or equal to  Those should be   for int i   0  i  lt  elements length  i       or  for int i   0  i  lt   elements length - 1  i       or  for int i   0  i   1  lt   elements length  i       The array   quot a quot    quot b quot   would iterate as   i   0 is  lt  2   elements 0  yields  quot a quot  i   1 is  lt  2   elements 1  yields  quot b quot   then exit the loop because 2 is not  lt  2  The incorrect examples both exit the loop prematurely and only execute with the first element in this simple case of two elements

User · Answer

You can do an enhanced for loop  for java 5 and higher  for iteration on array s elements   String   elements     a    a    a    a       for  String s  elements                     Do your stuff here     System out println s

User · Answer

String   elements      a    a    a    a      for  int i   0  i  lt  elements length - 1  i          String element   elements i       String nextElement   elements i 1       Note that in this case  elements length is 4  so you want to iterate from  0 2  to get elements 0 1  1 2 and 2 3

User · Answer

String   nameArray    John    Paul    Ringo    George        int numberOfItems   nameArray length      for  int i 0  i lt numberOfItems  i                  String name   nameArray i           System out println  Hello     name

User · Answer

String   elements      a    a   a   a      for  int i 0  i lt elements length-1  i          String s1   elements i       String s2   elements i 1

[java] Iterate through string array in Java

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