What are the overview and common methods of Java's ArrayList class?

1. Overview of the ArrayList class

What is a collection:

Provides a storage model with variable storage space, and the stored data capacity can change

ArrayList collection Features:

The bottom layer is implemented as an array, and the length can be changed

Use of generics:

Used to constrain the data type of elements stored in the collection

2. Common methods of ArrayList class

Construction method

Method name	Description
public ArrayList()	Create an empty collection object

Member method

Method Name	Description
public boolean remove(Object o)	Deletes the specified element and returns whether the deletion is successful
public E remove(int index)	Delete the element at the specified index and return the deleted element
public E set(int index,E element )	Modify the element at the specified index and return the modified element
public E get(int index)	Return the element at the specified index
public int size()	Returns the number of elements in the collection
public boolean add(E e)	Append the specified element to the end of this collection
public void add(int index,E element)	Specified in this collection Insert the specified element at the position

Sample code:

public class ArrayListDemo02 {
    public static void main(String[] args) {
        //创建集合
        ArrayList<String> array = new ArrayList<String>();
 
        //添加元素
        array.add("hello");
        array.add("world");
        array.add("java");
 
        //public boolean remove(Object o)：删除指定的元素，返回删除是否成功
        System.out.println(array.remove("world"));
        System.out.println(array.remove("javaee"));
 
        //public E remove(int index)：删除指定索引处的元素，返回被删除的元素
        System.out.println(array.remove(1));
        //IndexOutOfBoundsException
        System.out.println(array.remove(3));
 
        //public E set(int index,E element)：修改指定索引处的元素，返回被修改的元素
        System.out.println(array.set(1,"javaee"));
        //IndexOutOfBoundsException
        System.out.println(array.set(3,"javaee"));
 
        //public E get(int index)：返回指定索引处的元素
        System.out.println(array.get(0));
        System.out.println(array.get(1));
        System.out.println(array.get(2));
 
        //public int size()：返回集合中的元素的个数
        System.out.println(array.size());
 
        //输出集合
        System.out.println("array:" + array);
    }
}

3. ArrayList stores strings and traverses

Requirements: Create a storage character A collection of strings that stores 3 string elements. Use a program to traverse the collection on the console

Ideas:

1. Create a collection object

2. Add to the collection Add a string object

3. Traverse the collection. First, you must be able to obtain each element in the collection. This is achieved through the get(int index) method.

4. Traverse the collection. Secondly, you must be able to Get the length of the collection, which is implemented through the size() method

5. General format for traversing collections

Code implementation:

public class ArrayListTest01 {
    public static void main(String[] args) {
        //创建集合对象
        ArrayList<String> array = new ArrayList<String>();
        //往集合中添加字符串对象
        array.add("张三");
        array.add("李四");
        array.add("王五");
        //遍历集合，其次要能够获取到集合的长度，这个通过size()方法实现
        System.out.println(array.size());
        //遍历集合的通用格式
        for(int i=0; i<array.size(); i++) {
            String s = array.get(i);
            System.out.println(s);
        }
    }
}

4. ArrayList stores student objects and traverses

Requirements: Create a collection to store student objects, store 3 learning objects, and use a program to traverse the collection on the console

Ideas:

1. Define the student class

2. Create a collection object

3. Create a student object

4. Add a student object to the collection

5. Traverse the collection using general traversal Format implementation

Code implementation:

public class ArrayListTest02 {
    public static void main(String[] args) {
        //创建集合对象
        ArrayList<Student> array = new ArrayList<>();
        //创建学生对象
        Student s1 = new Student("张三", 30);
        Student s2 = new Student("李四", 33);
        Student s3 = new Student("王五", 28);
        //添加学生对象到集合中
        array.add(s1);
        array.add(s2);
        array.add(s3);
        //遍历集合，采用通用遍历格式实现
        for (int i = 0; i < array.size(); i++) {
            Student s = array.get(i);
            System.out.println(s.getName() + "," + s.getAge());
        }
    }

5. ArrayList stores student objects and traverses the upgraded version

Requirements: Create a collection to store student objects and store 3 student objects. Use a program to traverse the collection on the console. The student's name and age come from keyboard input

Ideas:

1. Define the student class. In order to facilitate keyboard input of data, put the student class in Member variables are all defined as String type

2. Create a collection object

3. Enter the data required for the student object with the keyboard

4. Create the student object and input the data with the keyboard Assign data to the member variables of the student object

5. Add the student object to the collection

6. Traverse the collection and use the general traversal format to implement

Code implementation:

public class ArrayListTest {
    public static void main(String[] args) {
        //创建集合对象
        ArrayList<Student> array = new ArrayList<Student>();
        //为了提高代码的复用性，我们用方法来改进程序
        addStudent(array);
        addStudent(array);
        addStudent(array);
        //遍历集合，采用通用遍历格式实现
        for (int i = 0; i < array.size(); i++) {
            Student s = array.get(i);
            System.out.println(s.getName() + "," + s.getAge());
        }
    }
    /*
        两个明确：
            返回值类型：void
            参数：ArrayList<Student> array
     */
    public static void addStudent(ArrayList<Student> array) {
        //键盘录入学生对象所需要的数据
        Scanner sc = new Scanner(System.in);
        System.out.println("请输入学生姓名:");
        String name = sc.nextLine();
        System.out.println("请输入学生年龄:");
        String age = sc.nextLine();
        //创建学生对象，把键盘录入的数据赋值给学生对象的成员变量
        Student s = new Student();
        s.setName(name);
        s.setAge(age);
        //往集合中添加学生对象
        array.add(s);
    }
}

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