list赋值方法add()...和set()简介

朱雀 2023-10-12 19:04 33阅读 0赞

**目录**

一、方法展示

二、add() 方法介绍

2.1.add（E element）

2.1.1源码

2.1.2.实例截图

2.1.3.Null引起的题外话

2.2.add(int index, E element)

2.2.1.源码

2.2.2.示例截图

2.2.3. add()引起IndexOutOfBoundsException简介

三、addAll()方法介绍

3.1.addAll

3.1.1.源码

3.1.2.代码示例

3.1.3.运行截图

四、set(int index,E element)

4.1.元素替换方法：set(int index,E element)

4.1.1.源码

--------------------

## 一、方法展示 ##

## ![580770be31664062809759beaabf7f6c.png][] ##

由上图可以看出，Java中线性表List接口的插入方法大概分为三大类，add、addAll和set。

## 二、add() 方法介绍 ##

### 2.1.add（E element） ###

#### 2.1.1源码 ####

![0f7ce441f35847e09a18251e083ce806.png][]

/**
         * Appends the specified element to the end of this list (optional
         * operation).
         * 将指定的元素追加到此list的末尾（可选操作）
         *
         * <p>Lists that support this operation may place limitations on what
         * elements may be added to this list.  
         * <p>支持此操作的列表可能会限制元素可以被添加到该list中。
         *
         * In particular, some lists will refuse to add null elements, and others will         
         * impose restrictions on the type of elements that may be added.  
         * 特别是一些list将拒绝添加null元素，其他列表将强制对可以添加的元素类型的限制。
         * 
         * List classes should clearly specify in their documentation any restrictions
         * on what elements may be added.
         * List类应该在其文档中明确规定任何限制关于可以添加哪些元素。
         *
         * @param e element to be appended to this list
         * @return <tt>true</tt> (as specified by {@link Collection#add})
         * @throws UnsupportedOperationException if the <tt>add</tt> operation
         *         is not supported by this list
         * @throws ClassCastException if the class of the specified element
         *         prevents it from being added to this list
         * @throws NullPointerException if the specified element is null and this
         *         list does not permit null elements
         * @throws IllegalArgumentException if some property of this element
         *         prevents it from being added to this list
         */
    
        boolean add(E e);

简单来说，此方法有三个要素：将新元素添加到list末尾、只能传入指定类型元素、部分list拒接添加null。

但据我所知，JDK中应该是没有原生的"NULL判断"来拒绝null的添加。

#### 2.1.2.实例截图 ####

![34a5d082bd3e4226bcc24cee5f1b3d8a.png][]

#### 2.1.3.Null引起的题外话 ####

Collection规范指出，当collection不支持null时，应引发NullPointerException。戳》》》[菜鸟教程Interface Collection<E>][Interface Collection_E] 但是，此操作不是必须的，所以看自己选择。![fa27ed5d20f942e1b67c0f8959d7e308.png][]

### 2.2.add(int index, E element) ###

#### 2.2.1.源码 ####

#### ![15c31cf411ec4013ab279f345485efbc.png][] ####

/**
         * Inserts the specified element at the specified position in this list
         * (optional operation).  
         * 在此列表中的指定位置插入指定的元素（可选操作）。
         * 
         * Shifts the element currently at that position (if any) and any subsequent 
         * elements to the right (adds one to their indices).
         * 将当前位于该位置的元素（如果有）和任何后续元素向右移动（在其索引中添加一个）。
         *
         * @param index index at which the specified element is to be inserted
         * @param element element to be inserted
         * @throws UnsupportedOperationException if the <tt>add</tt> operation
         *         is not supported by this list
         * @throws ClassCastException if the class of the specified element
         *         prevents it from being added to this list
         * @throws NullPointerException if the specified element is null and
         *         this list does not permit null elements
         * @throws IllegalArgumentException if some property of the specified
         *         element prevents it from being added to this list
         * @throws IndexOutOfBoundsException if the index is out of range
         *         (<tt>index < 0 || index > size()</tt>)
         */
    
        void add(int index, E element);

#### 2.2.2.示例截图 ####

![5f2c6352acd840e7b6f8b2fc6826f0f9.png][]

![f5095608061c4520a509758774e4644a.png][]

当①执行时，下标为1的元素A，将原本list中的元素2，3，4，5都给向后移动了。

当②和③执行时，新添加了元素B，但是出现了IndexOutOfBoundsException(下标越界异常)，由此可以看出，当使用 add(int index, E element) 时，需要满足两个条件之一：当前下标已经存在元素，或当前下标的前一个位置存在元素。

==》当list中没有元素时，add的下标就需要从0开始，否则也会出现下标越界问题。

#### 2.2.3. add()引起IndexOutOfBoundsException简介 ####

待补充...

## 三、addAll()方法介绍 ##

### 3.1.addAll ###

#### 3.1.1.源码 ####

![bd35a51c46c34b2cbeb8f142a99ea765.png][]

/**
         * Appends all of the elements in the specified collection to the end of
         * this list, in the order that they are returned by the specified
         * collection's iterator (optional operation).  
         * 按照指定集合的迭代器返回的顺序，将指定集合中的所有元素追加到此列表的末尾（可选操作）。
         *
         * The behavior of this operation is undefined if the specified collection is         
         * modified while the operation is in progress.  (Note that this will occur if the
         * specified collection is this list, and it's nonempty.)
         * 如果在操作进行期间修改了指定的集合，则此操作的行为是未定义的。
         * (请注意，如果指定的集合就是这个list，它不是空的。)
         *
         * @param c collection containing elements to be added to this list
         * @return <tt>true</tt> if this list changed as a result of the call
         * @throws UnsupportedOperationException if the <tt>addAll</tt> operation
         *         is not supported by this list
         * @throws ClassCastException if the class of an element of the specified
         *         collection prevents it from being added to this list
         * @throws NullPointerException if the specified collection contains one
         *         or more null elements and this list does not permit null
         *         elements, or if the specified collection is null
         * @throws IllegalArgumentException if some property of an element of the
         *         specified collection prevents it from being added to this list
         * @see #add(Object)
         */
    
        boolean addAll(Collection<? extends E> c);

![e2d546c0d2bf461c8a2a82a3da1583fe.png][]

由上述源码可知，addAll的两个方法与add的使用大体相同，都是在原list内添加或在原list指定位置添加，同时下标取值范围 不能符合(index < 0 || index > size())，不过

1、add添加的是元素，addAll添加的是 Collection<? extends E> c

2、add使用时，部分list中不允许添加null，但还是能在list中添加null元素的；

addAll则不允许添加null，但可以添加null元素

#### 3.1.2.代码示例 ####

package com.task.test;
    
    import java.util.ArrayList;
    import java.util.List;
    
    public class T1 {
    
        public static void main(String[] args) {
    
            List<String> list1 = new ArrayList<>();
            new T1().returnList1(list1);
    
            List<String> list2 = new ArrayList<>();
            new T1().returnList2(list2);
    
            List<String> list3 = new ArrayList<>();
            new T1().returnList3(list3);
    
            List<String> list4 = new ArrayList<>();
    
            List<String> list5 = null;
    
    
            List<String> listAll = new ArrayList<>();
            listAll.addAll(list1);
            System.out.println("1:listAll = " + listAll);
            listAll.addAll(list2);
            System.out.println("2:listAll = " + listAll);
            listAll.addAll(5,list3);
            System.out.println("3:listAll = " + listAll);
            listAll.addAll(list4);
            System.out.println("4:listAll = " + listAll);
            listAll.addAll(list5);
            System.out.println("5:listAll = " + listAll);
        }
    
        public void returnList1(List list){
            list.add("A1");
            list.add("B1");
            list.add("C1");
            list.add("D1");
            list.add("E1");
            list.add("F1");
            list.add("G1");
        }
        public void returnList2(List list){
            list.add("A2");
            list.add("B2");
            list.add("C2");
            list.add("D2");
            list.add("E2");
            list.add("F2");
            list.add("G2");
        }
    
        public void returnList3(List list){
            list.add(null);
        }
    }

#### 3.1.3.运行截图 ####

![5ad5449d95354ed8bc479607e2ea07d6.png][]

关于list4 和 list5 的区别，可以查看》》》[ArrayList初始化的小知识][ArrayList]

## 四、set(int index,E element) ##

### 4.1.元素替换方法：set(int index,E element) ###

#### 4.1.1.源码 ####

![4457fdd54294472ea0b1eb95785a7082.png][]

/**
         * Replaces the element at the specified position in this list with the
         * specified element (optional operation).
         * 将此列表中指定位置的元素替换为指定的元素（可选操作）。
         *
         * @param index index of the element to replace
         * @param element element to be stored at the specified position
         * @return the element previously at the specified position
         * @throws UnsupportedOperationException if the <tt>set</tt> operation
         *         is not supported by this list
         * @throws ClassCastException if the class of the specified element
         *         prevents it from being added to this list
         * @throws NullPointerException if the specified element is null and
         *         this list does not permit null elements
         * @throws IllegalArgumentException if some property of the specified
         *         element prevents it from being added to this list
         * @throws IndexOutOfBoundsException if the index is out of range
         *         (index < 0 || index >= size())
         */
    
        E set(int index, E element);

1、这是个元素替换方法。

2、使用set时的下标index 取值范围不能在(index < 0 || index >= size())之间。

[580770be31664062809759beaabf7f6c.png]: https://img-blog.csdnimg.cn/580770be31664062809759beaabf7f6c.png
[0f7ce441f35847e09a18251e083ce806.png]: https://img-blog.csdnimg.cn/0f7ce441f35847e09a18251e083ce806.png
[34a5d082bd3e4226bcc24cee5f1b3d8a.png]: https://img-blog.csdnimg.cn/34a5d082bd3e4226bcc24cee5f1b3d8a.png
[Interface Collection_E]: https://www.runoob.com/manual/jdk1.6/java.base/java/util/Collection.html
[fa27ed5d20f942e1b67c0f8959d7e308.png]: https://img-blog.csdnimg.cn/fa27ed5d20f942e1b67c0f8959d7e308.png
[15c31cf411ec4013ab279f345485efbc.png]: https://img-blog.csdnimg.cn/15c31cf411ec4013ab279f345485efbc.png
[5f2c6352acd840e7b6f8b2fc6826f0f9.png]: https://img-blog.csdnimg.cn/5f2c6352acd840e7b6f8b2fc6826f0f9.png
[f5095608061c4520a509758774e4644a.png]: https://img-blog.csdnimg.cn/f5095608061c4520a509758774e4644a.png
[bd35a51c46c34b2cbeb8f142a99ea765.png]: https://img-blog.csdnimg.cn/bd35a51c46c34b2cbeb8f142a99ea765.png
[e2d546c0d2bf461c8a2a82a3da1583fe.png]: https://img-blog.csdnimg.cn/e2d546c0d2bf461c8a2a82a3da1583fe.png
[5ad5449d95354ed8bc479607e2ea07d6.png]: https://img-blog.csdnimg.cn/5ad5449d95354ed8bc479607e2ea07d6.png
[ArrayList]: https://blog.csdn.net/weixin_52255395/article/details/130550572
[4457fdd54294472ea0b1eb95785a7082.png]: https://img-blog.csdnimg.cn/4457fdd54294472ea0b1eb95785a7082.png