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Tag: arraylist

Android NullPointer Attempt to invoke virtual method ‘boolean java.util.ArrayList.add(java.lang.Object)’ on a null object reference

I’m getting this error: java.lang.NullPointerException: Attempt to invoke virtual method ‘boolean java.util.ArrayList.add(java.lang.Object)’ on a null object reference and just to make it clear is that I know others with the same issue have asked the same question and I have read the solutions which are usually that you have to instantiate your ArrayList which however I am obviously doing but

How to return arraylist vertically

I am trying to return an array list vertically but I’m having some issues trying to implement it. Below is my code, and the return results; Output is what I’m trying to get to be vertically } My current output is [2, 4, -1] I’d like it to be Any help would be appreciated. Thank you in advance Answer Hi

Check if ArrayList Contains same array order ignored

I’ve initialized an ArrayList holding int arrays as such: ArrayList<int[]> holder = new ArrayList<int[]>(); If I add an int[] like this: int[] first = {1, 2, 3}; holder.add(first); If I do this check, I want the function to return true, but it returns false right now int[] second = {2, 1, 3}; if(holder.contains(second)) return true; else return false Answer You

Decrease the number of calls

I have arraylist of filenames (java) and I want to delete these files using rm but it is time consuming can I do batching using xargs or something else which can help to delete files faster. Answer Don’t use rm. Use Java. As others have pointed out, spawning a process is much slower than doing it in your program. Also,

How to cast an object of an ArrayList of objects (of type superclass) to an object of type subclass

If I have a superclass, let’s call it Car, with the constructor parameters String name, String color, double wheelSize, and a subclass of this, let’s call it Truck, with the constructor parameters String name, String color, double wheelSize, and double truckBedArea, and in the subclass (Truck), I have a method called modifyCar with the paramaters Car car, String newName, String

How can I convert arraylist to arraylist

My goal is to find on which specific index is String from ArrayList and add them to new ArrayList, So if house is [0] than i want to return new ArrayList with integer. At the begging I have ArrayList like this Input : And I want to get new ArrayList like this Output: Answer You can do it just by

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