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

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

    /*** 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

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> 但是，此操作不是必须的，所以看自己选择。

2.2.add(int index, E element)

2.2.1.源码

    /*** 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 &lt; 0 || index &gt; size()</tt>)*/void add(int index, E element);

2.2.2.示例截图

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

    /*** 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);

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

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

四、set(int index,E element)

4.1.元素替换方法：set(int index,E element)

4.1.1.源码

    /*** 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。