Java ArrayList

Java ArrayList: The Ultimate Guide

ArrayList is a powerful data structure in Java that enables dynamic size arrays to be implemented with ease. With its capabilities to grow and shrink in size, it is an essential part of any Java programmer’s toolkit. In this comprehensive guide, we will explore the ArrayList class in detail, including its creation, manipulation, and usage in real-world scenarios. （ArrayList是Java中功能强大的数据结构，可轻松实现动态大小数组。凭借其增长和缩小尺寸的能力，它是任何Java程序员工具包的重要组成部分。在本综合指南中，我们将详细探讨ArrayList类，包括其创建、操作和在现实场景中的使用。）

What is an ArrayList in Java? #

What is an ArrayList in Java? （Java中的ArrayList是什么？）

An ArrayList in Java is a resizable array implementation of the List interface. It allows for elements to be added and removed from the list dynamically, as opposed to the traditional arrays which have a fixed size. The ArrayList class is part of the Java Collection framework and offers a wide range of functionality that makes it an ideal choice for many programming tasks. （Java中的ArrayList是List接口的可调整大小的数组实现。它允许动态地从列表中添加和删除元素，而不是具有固定大小的传统数组。ArrayList类是Java集合框架的一部分，提供了广泛的功能，使其成为许多编程任务的理想选择。）

Creating an ArrayList #

Creating an ArrayList （创建ArrayList）

The process of creating an ArrayList in Java is simple and straightforward. The ArrayList class provides several constructors to choose from, including a default constructor, one that takes an initial capacity as an argument, and one that takes a Collection object. （在Java中创建ArrayList的过程简单明了。ArrayList类提供了几个可供选择的构造函数，包括一个默认构造函数，一个将初始容量作为参数，一个将Collection对象作为参数。）

ArrayList<Integer> numbers = new ArrayList<>();
ArrayList<String> names = new ArrayList<>(10);
ArrayList<Boolean> flags = new ArrayList<>(Arrays.asList(true, false, true));

Manipulating an ArrayList #

Manipulating an ArrayList （操作ArrayList）

One of the strengths of ArrayList is its ability to manipulate its elements with ease. Adding, removing, and modifying elements in an ArrayList can be accomplished with several methods provided by the ArrayList class. （ArrayList的优势之一是能够轻松操作其元素。在ArrayList中添加、删除和修改元素可以使用ArrayList类提供的多个方法来完成。）

Adding Elements #

Elements can be added to an ArrayList using the add method. This method takes an element as an argument and adds it to the end of the list. （可以使用add方法将元素添加到ArrayList。此方法将元素作为参数，并将其添加到列表的末尾。）

ArrayList<String> names = new ArrayList<>();
names.add("John");
names.add("Jane");
names.add("Jim");

Removing Elements #

Elements can be removed from an ArrayList using the remove method. This method takes either an index or an object as an argument and removes the corresponding element from the list. （可以使用remove方法从ArrayList中删除元素。此方法将索引或对象作为参数，并从列表中删除相应的元素。）

ArrayList<String> names = new ArrayList<>(Arrays.asList("John", "Jane", "Jim"));
names.remove(1); // removes "Jane"
names.remove("John"); // removes "John"

Modifying Elements #

Elements can be modified in an ArrayList using the set method. This method takes an index and an object as arguments and sets the element at the specified index to the given object. （可以使用set方法在ArrayList中修改元素。此方法将索引和对象作为参数，并将指定索引处的元素设置为给定对象。）

ArrayList<String> names = new ArrayList<>(Arrays.asList("John", "Jane", "Jim"));
names.set(1, "Jill"); // replaces "Jane" with "Jill"

Using an ArrayList in Real-World Scenarios #

Using an ArrayList in Real-World Scenarios （在真实场景中使用ArrayList）

ArrayList can be used in a variety of real-world scenarios, from simple tasks such as storing a list of names to more complex tasks such as representing a graph. In this section, we will explore some of the most common uses of ArrayList. （ArrayList可用于各种真实场景，从存储名称列表等简单任务到表示图形等更复杂的任务。在本节中，我们将探讨ArrayList的一些最常见用途。）

Storing a List of Objects #

ArrayList can be used to store a list of objects, such as strings, integers, or custom objects. This makes it an ideal choice for tasks such as reading data from a file or database and storing it in memory for processing. （ArrayList可用于存储对象列表，例如字符串、整数或自定义对象。这使其成为从文件或数据库读取数据并将其存储在内存中进行处理等任务的理想选择。）

ArrayList<Person>
people = new ArrayList<>();
people.add(new Person("John Doe", 30));
people.add(new Person("Jane Doe", 28));
people.add(new Person("Jim Smith", 35));

Implementing a Stack #

ArrayList can be used to implement a stack data structure, where elements are added and removed in a Last In First Out (LIFO) order. This can be accomplished by adding and removing elements from the end of the list. （ArrayList可用于实现堆栈数据结构，其中以最后进先出（ LIFO ）顺序添加和删除元素。这可以通过从列表末尾添加和删除元素来实现。）

ArrayList<Integer> stack = new ArrayList<>();
stack.add(1);
stack.add(2);
stack.add(3);
System.out.println(stack.remove(stack.size()-1)); // Outputs 3
System.out.println(stack.remove(stack.size()-1)); // Outputs 2
System.out.println(stack.remove(stack.size()-1)); // Outputs 1

Conclusion #

Conclusion （小结）

ArrayList is a versatile and essential data structure in Java, offering a dynamic and flexible way to store and manipulate elements. Whether it’s used to store a list of objects, implement a stack, or represent a graph, ArrayList is an indispensable tool for any Java programmer. With its ease of use and wide range of functionality, it’s no wonder that ArrayList is one of the most popular data structures in Java. （ArrayList是Java中一种多功能且必不可少的数据结构，提供了一种动态且灵活的方式来存储和操作元素。无论是用于存储对象列表、实现堆栈还是表示图形， ArrayList都是任何Java程序员不可或缺的工具。ArrayList具有易用性和广泛的功能，因此它是Java中最受欢迎的数据结构之一也就不足为奇了。）