CODEWITHSUNDEEP
javaarraylistreplace
Rafał Praczyk
Rafał Praczyk

Reputation: 441

Replace part of ArrayList with other ArrayList

Is there any simple way (for example library function) to replace fragment of one ArrayList with another ArrayList? What I want to do is:

 ArrayList<Byte> fileArr = // some bytes //
 ArrayList<Byte> toReplace = // some bytes I want to replace in fileArray //
 ArrayList<Byte> window = // window with bytes from file and size of toReplace List  //
 ArrayList<Byte> replacing = // bytes I want to replace with //
 for(int i = 0; i <= (maxElementOfFileArray - sizeOfToReplace); i++){
 window = fileArr.subList(i, i+sizeOfToReplace) 
 if(window.equals(toReplace){
      fileArr.replaceAll(i, toReplace, replacing) 
 }
i= indexOfReplacingListFinishInFileList -1; 
}

where the replaceAll function would replace elements of file ArrayList from index where subList toReplace occurs with elements of replacing list, and here's the catch: toReplace and replacing may be diffrent size Lists. Because if they would be the same size I just would do that with set function of ArraList in "for(E e : elements)" . So replace function can change size of file ArrayList it's changing.

Upvotes: 3

Views: 4054

Answers (3)

TechTrip
TechTrip

Reputation: 4537

Write a utility method to accept a generic array and replace a given subarray, if found, with all the possible checks.

You can test for the presence of the subarray:

    int firstIndex = Collections.indexOfSubList(source, target);

    if (firstIndex == -1 ){
        // the sublist doesn't exist
    }

    int lastIndex = Collections.lastIndexOfSubList(source, target);

From there you have your insertion points and can use a library to insert or write a brute force method. For instance you can get the sublist from the List interface and make the changes to that sublist.

Upvotes: 0

Philippe Banwarth
Philippe Banwarth

Reputation: 17725

You can clear, then add the new elements to the window.

By the ways you can use Collections.indexOfSubList to find the window position.

    List<Byte> fileArr = new ArrayList(Arrays.asList(new Byte[]{1, 2, 3, 4, 5, 6}));
    List<Byte> toReplace = Arrays.asList(new Byte[]{3, 4});
    List<Byte> replacing = Arrays.asList(new Byte[]{13, 14, 15, 16, 17, 18});

    int idx = Collections.indexOfSubList(fileArr, toReplace);

    if (idx >= 0) {
        List<Byte> window = fileArr.subList(idx, idx + toReplace.size());
        window.clear();
        window.addAll(replacing);
    }

    System.out.println(fileArr);


    [1, 2, 13, 14, 15, 16, 17, 18, 5, 6]

Upvotes: 2

vikingsteve
vikingsteve

Reputation: 40378

You could try

fileArr.removeRange(i, i+sizeOfToReplace);
fileArr.addAll(i, replacing);

Upvotes: 4

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