Array Length Vs Arraylist Size Inward Java

One of the confusing purpose inwards learning Java for a beginner to empathize how to detect the length of array too ArrayList inwards Java? Main argue for the confusion is an inconsistent means of calculating length betwixt two. Calling size() method on arrays too length, or fifty-fifty length() on ArrayList is mutual programming mistake made yesteryear beginners. The principal argue for confusion is the special treatment of an array inwards Java.  Java native arrays accept built-in length attribute exactly no size() method spell the Java library containers, known every bit Collection classes e.g. ArrayList<>, Vector<>, etc,  all accept a size() method. There is 1 to a greater extent than affair which adds to this confusion, that is capacity, at whatever indicate capacity of whatever collection class is the maximum release of elements collection tin hold. the size of collection must endure less than or equal to its capacity.

Though inwards reality, collection resize themselves fifty-fifty earlier it reaches its capacity, controlled yesteryear laod factor.  I accept mentioned this earlier on my post service difference betwixt ArrayList too Array inwards Java, if y'all non read it already, y'all may detect roughly useful exceptional in that location every bit well.

So, utilization length attribute to acquire release of elements inwards a array, likewise known every bit length, too for same affair inwards Collection classes e.g. ArrayList, Vector, utilization size() method. To give y'all to a greater extent than context, watch next lines of code, tin y'all spot the error, which is bothering our beginner friend:

Array length vs ArrayList Size

import java.util.*;   public class ArrayListTest {     public static void main(String[] args) {         ArrayList<String> arrList = new ArrayList<String>();         String[] items = { "One", "Two", "Three", "Four", "Five" };         for(String str: items){             arrList.add(str);         }         int size = items.size();         System.out.println(size);     } }

initialize ArrayList inwards 1 line every bit shown inwards next illustration :

Arrays.asList("First", "Second", "Third", "Fourth", "Fifth");

It's handy means to declare too initialize ArrayList inwards same place, similar to array inwards Java.  So adjacent fourth dimension don't confuse betwixt length too size(), array are special object inwards Java too has attribute called length, which specifies release of buckets inwards array, spell ArrayList is a Collection class, which inherit size() method, which returns release of elements within Collection. Remember, size is dissimilar than capacity of collection. At whatever point, size <= capacity of collection.

Further Learning
Java In-Depth: Become a Complete Java Engineer
Java Fundamentals: Collections
Data Structures too Algorithms: Deep Dive Using Java
Algorithms too Data Structures - Part 1 too 2
Data Structures inwards Java nine yesteryear Heinz Kabutz