我想知道如何将一组字符串类型的数组列表添加到数组列表中

Question

I want to add a set of string type arraylist objects into a another arraylist to store that string type arraylist objects.

ex: [[<, int, char], [12, &&, text], [<<, ||], [., .]]

I have created a string type arraylist to store string values. And another ArrayList type arraylist to store string type arraylists.

I give file path as input. That file has content like this

while (j < 6 || j > 90) {
            i = 1;
            while (i < 6) {
                System.out.print("* ");
                i++;
            }
            System.out.println();
            j++;
    }

    switch ( rt ) {
        case t1:

        case 12:

        case e3:

        case 43e:
    }
}

csCalculator sizeObject = new csCalculator();

                    List<Integer> csMarkList = new ArrayList<Integer>();
                    ArrayList<String> singleLineIdentiedTokens = new ArrayList<>();
                    Collection<ArrayList<String>> allLineIdentiedTokens = new ArrayList<>();
                    int returnCsMark = 0;

                    for(String obj:list)  {
                        singleLineIdentiedTokens = (ArrayList<String>) sizeObject.calcCsOfStatement(obj);                       
                        csMarkList.add(singleLineIdentiedTokens.size());
                        allLineIdentiedTokens.add(singleLineIdentiedTokens);

                        System.out.println(singleLineIdentiedTokens);
                        System.out.println(allLineIdentiedTokens);

                        if (!(singleLineIdentiedTokens.isEmpty())) {
                            singleLineIdentiedTokens.clear();
                        }

                     } 
                    System.out.println("CS MARK OF STATEMENT");
                    System.out.println(singleLineIdentiedTokens);
                    System.out.println(csMarkList);

I want expected an array like this. [[<, int, char], [12, &&, text], [<<, ||], [., .]]

But it gives an array with last string arraylist replacing all the previous arraylist objects like this.

[[., .], [., .], [., .], [., .]]

I want correct that replacing defect.

Answer 1

You're repeatedly adding singleLineIdentiedTokens to allLineIdentiedTokens . This means that all these adds refer to the same ArrayList. Your println(allLineIdentiedTokens) will print something like this:

[singleLineIdentiedTokens.toString(), singleLineIdentiedTokens.toString(), ... ]

That is exactly what you're seeing, as you get: [[., .], [., .], [., .], [., .]] . As you can see, the only value being kept is the last value assigned to singleLineIdentiedTokens . You can remedy this by altering the code as so:

... //logic
for(String obj:list)  {
    singleLineIdentiedTokens = (ArrayList<String>) sizeObject.calcCsOfStatement(obj);                       
    csMarkList.add(singleLineIdentiedTokens.size());
    allLineIdentiedTokens.add(new ArrayList<>(singleLineIdentiedTokens));// <- change this line

    System.out.println(singleLineIdentiedTokens);
    System.out.println(allLineIdentiedTokens);

    if (!(singleLineIdentiedTokens.isEmpty())) {
        singleLineIdentiedTokens.clear();
    }
}
... //more logic

What this does is keep a copy of singleLineIdentiedTokens at the current point in time, instead of repeatedly adding one reference that could change in value later.