The source code for clear(): public void clear() { modCount++; // Let gc do its work for (int i = 0; i < size; i++) elementData[i] = null; size = 0; } The source code for removeAll()(As defined in AbstractCollection): public boolean removeAll(Collection<?> c) { boolean modified = false; Iterator<?> e = iterator(); while (e.hasNext()) … Read more
ArrayList implements the List Interface. If you look at the Javadoc for List at the contains method you will see that it uses the equals() method to evaluate if two objects are the same.
You’re confusing the size of the array list with its capacity: the size is the number of elements in the list; the capacity is how many elements the list can potentially accommodate without reallocating its internal structures. When you call new ArrayList<Integer>(10), you are setting the list’s initial capacity, not its size. In other words, … Read more
In Java 8 or later: String listString = String.join(“, “, list); In case the list is not of type String, a joining collector can be used: String listString = list.stream().map(Object::toString) .collect(Collectors.joining(“, “));
After API 11 the SharedPreferences Editor accepts Sets. You could convert your List into a HashSet or something similar and store it like that. When you read it back, convert it into an ArrayList, sort it if needed and you’re good to go. //Retrieve the values Set<String> set = myScores.getStringSet(“key”, null); //Set the values Set<String> … Read more
Collections.reverse(aList); Example (Reference): ArrayList aList = new ArrayList(); //Add elements to ArrayList object aList.add(“1”); aList.add(“2”); aList.add(“3”); aList.add(“4”); aList.add(“5”); Collections.reverse(aList); System.out.println(“After Reverse Order, ArrayList Contains : ” + aList);
Use an Iterator and call remove(): Iterator<String> iter = myArrayList.iterator(); while (iter.hasNext()) { String str = iter.next(); if (someCondition) iter.remove(); }
Fixed size List The easiest way, that I know of, is to create a fixed-size single element List with Arrays.asList(T…) like // Returns a List backed by a varargs T. return Arrays.asList(s); Variable size List If it needs vary in size you can construct an ArrayList and the fixed-sizeList like return new ArrayList<String>(Arrays.asList(s)); and (in … Read more
If you are using java-8 there’s also another way to do this. int[] arr = list.stream().mapToInt(i -> i).toArray(); What it does is: getting a Stream<Integer> from the list obtaining an IntStream by mapping each element to itself (identity function), unboxing the int value hold by each Integer object (done automatically since Java 5) getting the … Read more
Differences Vectors are synchronized, ArrayLists are not. Data Growth Methods Use ArrayLists if there is no specific requirement to use Vectors. Synchronization If multiple threads access an ArrayList concurrently then we must externally synchronize the block of code which modifies the list either structurally or simply modifies an element. Structural modification means addition or deletion … Read more