Add ArrayList to another ArrayList in java

Then you need a ArrayList of ArrayLists: ArrayList<ArrayList<String>> nodes = new ArrayList<ArrayList<String>>(); ArrayList<String> nodeList = new ArrayList<String>(); nodes.add(nodeList); Note that NodeList has been changed to nodeList. In Java Naming Conventions variables start with a lower case. Classes start with an upper case.

How to remove specific object from ArrayList in Java?

ArrayList removes objects based on the equals(Object obj) method. So you should implement properly this method. Something like: public boolean equals(Object obj) { if (obj == null) return false; if (obj == this) return true; if (!(obj instanceof ArrayTest)) return false; ArrayTest o = (ArrayTest) obj; return o.i == this.i; } Or public boolean equals(Object … Read more

Java Generic with ArrayList

ArrayList<? extends A> means an ArrayList of some unknown type that extends A. That type might not be C, so you can’t add a C to the ArrayList. In fact, since you don’t know what the ArrayList is supposed to contain, you can’t add anything to the ArrayList. If you want an ArrayList that can … Read more

ArrayList vs LinkedList from memory allocation perspective

LinkedList might allocate fewer entries, but those entries are astronomically more expensive than they’d be for ArrayList — enough that even the worst-case ArrayList is cheaper as far as memory is concerned. (FYI, I think you’ve got it wrong; ArrayList grows by 1.5x when it’s full, not 2x.) See e.g. https://github.com/DimitrisAndreou/memory-measurer/blob/master/ElementCostInDataStructures.txt : LinkedList consumes 24 … Read more

How does ArrayList work?

Internally an ArrayList uses an Object[]. As you add items to an ArrayList, the list checks to see if the backing array has room left. If there is room, the new item is just added at the next empty space. If there is not room, a new, larger, array is created, and the old array … Read more

Time complexity of contains(Object o), in an ArrayList of Objects

O(n) The size, isEmpty, get, set, iterator, and listIterator operations run in constant time. The add operation runs in amortized constant time, that is, adding n elements requires O(n) time. All of the other operations run in linear time (roughly speaking). The constant factor is low compared to that for the LinkedList implementation. http://download.oracle.com/javase/6/docs/api/java/util/ArrayList.html

How can I create an array in Kotlin like in Java by just providing a size?

According to the reference, arrays are created in the following way: For Java’s primitive types there are distinct types IntArray, DoubleArray etc. which store unboxed values. They are created with the corresponding constructors and factory functions: val arrayOfZeros = IntArray(size) //equivalent in Java: new int[size] val numbersFromOne = IntArray(size) { it + 1 } val … Read more