I need to add elements to an ArrayList queue whatever, but when I call the function to add an element, I want it to add the element at the beginning of the array (so it has the lowest index) and if the array has 10 elements adding a new results in deleting the oldest element … Read more
How can I split an ArrayList (size=1000) in multiple ArrayLists of the same size (=10) ? ArrayList<Integer> results; 21 Answers 21
I need help with this java please. I created an ArrayList of bulbs, and I’m trying to replace a bulb at specific index with another bulb. So with the following heading, how do I proceed? public void replaceBulb(int index, Bulbs theBulb) { } 7 Answers 7
I was reading Java’s ArrayList source code and noticed some comparisons in if-statements. In Java 7, the method grow(int) uses if (newCapacity – minCapacity < 0) newCapacity = minCapacity; In Java 6, grow didn’t exist. The method ensureCapacity(int) however uses if (newCapacity < minCapacity) newCapacity = minCapacity; What was the reason behind the change? Was … Read more
I have an ArrayList l1 of size 10. I assign l1 to new list reference type l2. Will l1 and l2 point to same ArrayList object? Or is a copy of the ArrayList object assigned to l2? When using the l2 reference, if I update the list object, it reflects the changes in the l1 … Read more
I have two arraylist filelist and imgList which related to each other, e.g. “H1.txt” related to “e1.jpg”. How to automatically randomized the list of imgList according to the randomization of fileList? Like in excel, if we sort certain column, the other column will automatically follow? String [] file = {“H1.txt”,”H2.txt”,”H3.txt”,”M4.txt”,”M5.txt”,”M6.txt”}; ArrayList<String> fileList = new ArrayList<String>(Arrays.asList(file)); … Read more
I have an ArrayList that I want to iterate over. While iterating over it I have to remove elements at the same time. Obviously this throws a java.util.ConcurrentModificationException. What is the best practice to handle this problem? Should I clone the list first? I remove the elements not in the loop itself but another part … Read more
This question already has answers here: Create ArrayList from array (40 answers) Initialization of an ArrayList in one line (33 answers) Closed 5 years ago. I am aware that you can initialize an array during instantiation as follows: String[] names = new String[] {“Ryan”, “Julie”, “Bob”}; Is there a way to do the same thing … Read more
I try to add objects to a List<String> instance but it throws an UnsupportedOperationException. Does anyone know why? My Java code: String[] membersArray = request.getParameterValues(‘members’); List<String> membersList = Arrays.asList(membersArray); for (String member : membersList) { Person person = Dao.findByName(member); List<String> seeAlso; seeAlso = person.getSeeAlso(); if (!seeAlso.contains(groupDn)){ seeAlso.add(groupDn); person.setSeeAlso(seeAlso); } } The error message: java.lang.UnsupportedOperationException java.util.AbstractList.add(Unknown … Read more
Assuming that arraylist is defined as ArrayList<String> arraylist, is arraylist.removeAll(arraylist) equivalent to arraylist.clear()? If so, can I assume that the clear() method is more efficient for emptying the array list? Are there any caveats in using arraylist.removeAll(arraylist) instead of arraylist.clear()? 9 Answers 9
