Replace part of ArrayList with other ArrayList

Question

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.

vikingsteve · Accepted Answer · 2014-09-18 11:07:53Z

4

You could try

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

answered Sep 18, 2014 at 11:07

vikingsteve

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2 Comments

Erik Vesteraas Over a year ago

Checking the code of ArrayList, this mostly does the work using System.arraycopy, so should not be terribly slow. There is one loop nulling the data on the end of the array, so if you're doing this a lot, consider testing if a custom method is more efficient.

Rafał Praczyk Over a year ago

Yet, removeRange is protected AbstractList function, so I was forced to call it indirectly with "fileArr.subList(i, i + sizeOfToReplace).clear()". Thank you very much.

Philippe Banwarth · Accepted Answer · 2014-09-18 11:30:35Z

2

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]

answered Sep 18, 2014 at 11:30

Philippe Banwarth

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Comments

TechTrip · Accepted Answer · 2014-09-18 11:41:37Z

0

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.

edited Sep 18, 2014 at 11:41

answered Sep 18, 2014 at 11:33

TechTrip

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