Java中的数组与数组列表

让我们在标题中简要讨论数组和ArrayList的概念，以结合对Java程序的理解，以便稍后登陆它们之间的决定性差异。众所周知，数组是线性数据结构，提供了在内存地址空间中以连续方式添加元素的功能，而 ArrayList 是属于 Collection 框架的类。作为一名优秀的程序员，尽管知道这两者之间的区别，但他已经意识到在数组上使用 ArrayList。现在继续前进，即使使用 ArrayList 也有一个功能可以传递应该存储在 ArrayList 中的元素的数据类型类型，可以是对象、字符串、整数、双精度、浮点数等。

Note: As a side note, ArrayList in Java can be seen as similar to vector in C++. 

创建数组的方法

在Java中，以下是创建数组的两种不同方法。

1. 简单的固定大小数组
2. 动态大小的数组

int arr[] = new int[10]   

语法：声明一个静态数组数组

它可以进一步定义为两种类型：

• 类型 1 ：同时声明和初始化
• 类型 2：声明而不是稍后初始化元素。

类型 1

Type array_name [array_size] ;
Type array_name = { Element1, Element2, Element3, Element4,...., ElementN } ;
// It is preferable if we have very limited array elements 

类型 2

int arr [100] ;
// This does means we are declaring a memory block named 'arr' 
// which is containing continuous 100 block associated in it

Note: arr(0) returns the first element of the array so it does mean that if we try to print out arr(0) then we will get Element1. It is very important statement and is left unveiliable when it comes to deep understanding of memory storage in arrays.

现在让我们详细讨论 ArrayList 的下一个概念，如下所示

语法：声明一个 Arraylist

Arraylist al = new ArrayList ;
// Here Type is the type of elements in ArrayList to be created

Note: ArrayList in Java (equivalent to vector in C++) having dynamic size. It can be shrunk or expanded based on size. ArrayList is a part of the collection framework and is present in java.util package. 

现在让我们借助 Array 和 ArrayList 之间的差异来说明示例

Base 1：数组是Java提供的基本功能。 ArrayList 是Java中集合框架的一部分。因此使用 [] 访问数组成员，而 ArrayList 有一组方法来访问元素并修改它们。

例子：

Java

// Java program to demonstrate differences between
// Array and ArrayList
 
// Importing required classes
import java.util.ArrayList;
import java.util.Arrays;
 
// Main class
class GFG {
   
    // Main driver method
    public static void main(String args[])
    {
        // Input array
        int[] arr = new int[2];
        arr[0] = 1;
        arr[1] = 2;
 
        // Printing first element of array
        System.out.println(arr[0]);
 
        // ArrayList
        // Creating an arrayList with initial capacity
        // say bi it 2
        ArrayList arrL = new ArrayList(2);
 
        // Adding elements to ArrayList
        // using add() method
        arrL.add(1);
        arrL.add(2);
 
        // Printing alongside accessing
        // elements of ArrayList
        System.out.println(arrL.get(0));
    }
}

Java

import java.util.ArrayList;
class Test
{
    public static void main(String args[])
    {
       // allowed
        int[] array = new int[3];
 
        // allowed, however, need to be initialized
        Test[] array1 = new Test[3];
 
        // not allowed (Uncommenting below line causes
        // compiler error)
        // ArrayList arrL = new ArrayList();
 
        // Allowed
        ArrayList arrL1 = new ArrayList<>();
        ArrayList arrL2 = new ArrayList<>();
        ArrayList