What are the common methods of List in Java basics

1. Introduction to List interface

List is an ordered collection and a repeatable collection. It inherits the Collection interface. Repeated elements can appear in the List collection, and the element at the specified position can be accessed through the index (subscript).

2. List common methods - void add (int index, Obejct element) method

1. The void add (int index, Obejct element) method is to insert the element element into the specified Position, the following element is moved one element back.

2.void add(int index,Object element) method example:

import java.util.ArrayList; import java.util.List; public class p6 { public static void main(String[] args) {         // TODO Auto-generated method stub         List l = new ArrayList();         l.add("Java");         l.add("数据库原理及其应用");         l.add("软件测试");         l.add("Python实战");         //l集合所有的元素         System.out.println("l集合所有的元素"+l);         //在指定位置插入元素         l.add(1,"数据结构");         //插入元素后l集合所有元素         System.out.println("插入元素后l集合所有元素"+l);     } }

The result of the operation is:

3. List Commonly used methods - boolean addAll (int index, Collection c) method

1. The boolean addAll (int index, Collection c) method is: insert all elements of collection c into the specified position of the List collection.

2.boolean addAll(int index,Collection c) method example:

import java.util.ArrayList; public class p7 { public static void main(String[] args) {         // TODO Auto-generated method stub         ArrayList<string> a1 = new ArrayList<string>();         a1.add("Java");         a1.add("数据库原理及其应用");         a1.add("C语言");         System.out.println("a1的所有元素："+a1);         ArrayList<string> a2 = new ArrayList<string>();         a2.add("软件测试");         a2.add("Python实战");         a2.add("Java EE");         System.out.println("a2的所有元素："+a2);         //在a1指定位置插入a2所有元素         a1.addAll(2,a2);         System.out.println("在a1指定位置插入a2所有元素，a1的所有元素有："+a1);     } }</string></string></string></string>

The running result is:

four , List common methods - Object get (int index) method

1. The Object get (int index) method returns the element at the specified position in the List collection.

2.Object get(int index) method example

import java.util.ArrayList; public class p8 { public static void main(String[] args) {         // TODO Auto-generated method stub         ArrayList<string> a = new ArrayList<string>();         a.add("软件测试");         a.add("Java");         a.add("Python实战");         a.add("PHP+MYSQL");         System.out.print("索引值为3的元素："+a.get(3));     } }</string></string>

The running result is:

5. Common methods of List—&mdash ;Object remove(int index) method

1.Object remove(int index) method is to delete the element at the specified position.

2.Object remove(int index) method example

import java.util.ArrayList; public class p8 { public static void main(String[] args) {         // TODO Auto-generated method stub         ArrayList<string> a = new ArrayList<string>();         a.add("软件测试");         a.add("Java");         a.add("Python实战");         a.add("PHP+MYSQL");         System.out.println("删除索引值为3的元素："+a.remove(3));         System.out.println("a中所有的元素："+a);     } }</string></string>

The result of the operation is:

6. List common methods— —int indexOf(Object o) method

1. The int indexOf(Object o) method returns the index of the position where object o appears in the List collection. If object o does not appear, it returns -1.

2. The code is as follows:

import java.util.ArrayList; public class p9 { public static void main(String[] args) {         // TODO Auto-generated method stub         ArrayList<string> a = new ArrayList<string>();         a.add("软件测试");         a.add("Java");         a.add("Python实战");         a.add("PHP+MYSQL");         System.out.println("a中所有的元素有："+a);         int num=a.indexOf("Python实战");         System.out.println("第一次出现\"Python实战\"的索引值为："+num);         num=a.indexOf("数据结构");         System.out.println("第一次出现\"数据结构\"的索引值为："+num);       } }</string></string>

The result of the operation is:

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