CODEWITHSUNDEEP
javalist
Tony
Tony

Reputation: 2748

Need help in list Java

Not sure how I can achieve this. I have a object list, where it consists of multiple data example

ABC1231211
ABC1231111
ABC4562222
ABC4562456

Now I trying to seperate the list according to their code, which is 123 and 456, and add header and tailer to them. So my expected result would be

Head
ABC1231211
ABC1231111
Tail

Head2
ABC4562222
ABC4562456
Tail2

But the result I get is 

Head
ABC1231211
Tail

Head
ABC1231111
Tail

Head2
ABC4562222
Tail2

Head2
ABC4562456
Tail2

Code

 @Override
    public List process(List<Detail> l) throws Exception {

        for (Detail d : l) {
            if (d.Code().equals("123")) {
                list = generateS(d);
            }
            if (d.Code().equals("456")) {
                list = generateR(d);
            }
        }

        return list;
    }


 public List<String> generateS(Detail d) throws Exception {

        try {
            list.add(new HDR("Head").getHeader());

            DetailL x = new DetailL();
            x.setType(d.getType());
            ....

            list.add(x.getDetail());

            list.add(new TLR("Tail").getTailer());
        } catch (Exception ex) {
            throw new BatchException(DetailProcessor.class, ex);
        }
        return list;
    }

Any help would be much appreciated

Upvotes: 1

Views: 116

Answers (4)

daniu
daniu

Reputation: 14999

If you're using Java 8, you can use streams:

public void process(List<Detail> details) throws Exception {

    Map<String, List<Detail>> byCode =
        details.stream().collect(Collectors.groupingBy(Detail::getCode));

    byCode.entrySet().stream().forEach(entry -> {
        System.out.println(headerFromType(entry.getKey()));
        entry.getValue().foreach(System.out::println);
        System.out.println(tailFromType(entry.getKey()));
}

with headerFromType and tailFromType returning "Head"/"Head2" or "Tail"/"Tail2", depending on the given type.

Upvotes: 1

Stefan
Stefan

Reputation: 2385

Here is another implemetation that takes another approach:

private void go() {
    List<String> list = new ArrayList<>();
    list.add("ABC1231211");
    list.add("ABC1231111");
    list.add("ABC4562222");
    list.add("ABC4562456");

    String lastTag = null;
    int startPos = 0;
    for (int i = 0; i < list.size(); i++) {
        String tag = list.get(i).substring(3, 6);
        if (!tag.equals(lastTag) && lastTag != null) {
            print(list.subList(startPos, i));
            startPos = i;
        }
        lastTag = tag;
    }
    print(list.subList(startPos, list.size()));
}

private void print(List<String> list) {
    System.out.println("Head");
    for (String item : list) {
        System.out.println(item);
    }
    System.out.println("Tail");
}

Simply "If you come accross an element with a different tag, print the previous sublist". (And print whatever is left at the end since that sublist's printout is not triggered by a new tag.)

Upvotes: 1

pwain
pwain

Reputation: 279

You create a new header and a new tail every time you call generateS or generateR but you should just create a new header once if you find a new code ( for example 123).

Solution: You collect your details into a list before you call generateS or generateR and put all the details from collected list into your DetailL.

Upvotes: 1

Haem
Haem

Reputation: 929

You are generating a new head and tail for each element instead of adding to the already-generated list.

For each Detail, you should first check if the list exists, and if it doesn't, then call generateS or generateR as appropriate. If the list exists, you want to call e.g. sList.add(sList.size()-1, d.getDetail()). You'll of course want to replace the call d.getDetail() with the value that's supposed to go into the list or a method call that returns that value.

Then you probably want to use list.addAll(sList) to add the generated lists' contents to list.

Another solution is to generate the combined list on demand, and store the two lists separately. In that case, you would check if the corresponding list is null in the beginning of generateS or generateR, and initialize it if it is.

Upvotes: 1

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