How to interchange List<List<String>> array values using index in java?

Question

I am having List<List<String>> data this way,

List<List<String>> repdata = [
    ["1185","R","4t","G","06","L","GT","04309","2546","2015","CF FE","01H1","20","23840","FF20"],
    ["1186","R","5t","R","01","L","TP","00110","1854","2016","FE LL","06W3","01","19065","FB01"],
    ["1187","R","6t","H","06","L","TP","04333","1864","2015","CF FE SL","0209","FD22","19845",null],
    ["1188","R","7t","H","06","L","PR","04041","6951","2015","CC CT FE GN PC","0070","00","36590","LB00"],
    ["1189","R","8t","H","06","L","WS","04290","4450","2014","CF   EN   FE   PC   TP","0070","EA30","28320.00",null],
    ["1190","R","9t","H","06","L","LA","04915","4430","2015","CF DK FE RR TC","0040","10","23680","FB10"],
    ["1191","R","10t","H","06","L","LF","04335","2532","2015","CF FE GE","0040","FC10","22970",null],
    ["1192","R","11t","H","06","L","SA","04772","8345","2015","BZ C8 FE","01D6","13","33390","LC13"]]

I want to compare and interchange elements in each inner list : particularly values at 12th and 14th indexes in the innerlists.

ex: in this inner list data

[["1185","R","4t","G","06","L","GT","04309","2546","2015","CF FE","01H1","20","23840","FF20"]]

I want to compare and interchange '20' with 'FF20' using this logic .

    If 14th index value != null then assign,

       12th index=14th index value.

    else if 14th index value ==null,

then leave 12th index=12th index value as it is.

And this has to be repeated for all the inner lists in the List<List<String>> repdata.

So, my final List> would be this way,

List<List<String>> repdata = [
["1185","R","4t","G","06","L","GT","04309","2546","2015","CF FE","01H1","FF20","23840","FF20"],//interchange 12th with 14th as 14th !=null
["1186","R","5t","R","01","L","TP","00110","1854","2016","FE LL","06W3","FB01","19065","FB01"],//interchange 12th with 14th as 14th !=null
["1187","R","6t","H","06","L","TP","04333","1864","2015","CF FE SL","0209","FD22","19845",null],//leave 12th as IT IS as 14th ==null
["1188","R","7t","H","06","L","PR","04041","6951","2015","CC CT FE GN PC","0070","00","36590","LB00"],//interchange 12th with 14th as 14th !=null
["1189","R","8t","H","06","L","WS","04290","4450","2014","CF   EN   FE   PC   TP","0070","EA30","28320.00",null],//leave 12th as IT IS as 14th ==null
["1190","R","9t","H","06","L","LA","04915","4430","2015","CF DK FE RR TC","0040","10","23680","FB10"],//interchange 12th with 14th as 14th !=null
["1191","R","10t","H","06","L","LF","04335","2532","2015","CF FE GE","0040","FC10","22970",null],//leave 12th as IT IS as 14th ==null
["1192","R","11t","H","06","L","SA","04772","8345","2015","BZ C8 FE","01D6","13","33390","LC13"]]//interchange 12th with 14th as 14th !=null

I tried removing 12th index and then adding 14th index value at 12th index.

But i am continuously getting concurrentmodificationexception.

Can anyone help me in this issue?

Answer 1

In order to replace the 12th element of a list with the 14th element, you'll have to write code as follows:

List<List<String>> listOfLists = ...;
for( List<String> list: listOfLists ){
    String el;
    if( list.size() > 14 &&              // list is long enough
        (el = list.get(14)) != null ){   // element is not null
        list.set( 12, el );              // replace element at index 12
    }  
}