目录
List 接口
1. 特性描述
A List is an ordered Collection (sometimes called a sequence). Lists may contain duplicate elements.列表是有序的集合（有时称为序列）。 列表可能包含重复的元素。The Java platform contains two general-purpose List implementations. ArrayList, which is usually the better-performing implementation, and LinkedList which offers better performance under certain circumstances.Java 平台包含两个常用的 List 实现。 ArrayList 通常是性能较好的实现，而 LinkedList 在某些情况下可以提供更好的性能。
List 接口常用方法
E get ( int index ); // 获取给定位置的元素E set ( int index , E element ); // 修改给定位置的元素void add ( int index , E element ); // 在给定位置插入一个元素E remove ( int index ); // 移除给定位置的元素int indexOf ( Object o ); // 获取给定元素第一次出现的下标int lastIndexOf ( Object o ); // 获取给定元素最后一次出现的下标ListIterator < E > listIterator (); // 获取 List 集合专有的迭代器ListIterator < E > listIterator ( int index ); // 获取 List 集合专有的迭代器，从给定的下标位置开始的迭代器List < E > subList ( int fromIndex , int toIndex ); // 获取 List 集合的一个子集合
2. ArrayList
示例及源码解读
import java . util . ArrayList ;import java . util . Iterator ;import java . util . List ;import java . util . ListIterator ;public class ArrayListTest {public static void main ( String [] args ) {//集合有序是指存储顺序与遍历时取出来的顺序一致ArrayList < String > list = new ArrayList <> ();list . add ( "a" ); // 第一次调用 size =0;list . add ( "a" );list . add ( "b" );list . add ( "c" );list . add ( "d" );list . add ( 2 , "n" ); // a a b c d => a a b b c d => a a n b c dString old = list . set ( 1 , "g" );System . out . println ( old );System . out . println ( "====================" );for ( String str : list ){System . out . println ( str );}System . out . println ( "====================" );Iterator < String > iter = list . iterator ();while ( iter . hasNext ()){String s = iter . next ();System . out . println ( s );}System . out . println ( "====================" );ListIterator < String > listIterator = list . listIterator ();while ( listIterator . hasNext ()){String s = listIterator . next ();System . out . println ( s );}System . out . println ( "====================" );ListIterator < String > prevIterator = list . listIterator ( list . size ());while ( prevIterator . hasPrevious ()){String s = prevIterator . previous ();System . out . println ( s );}System . out . println ( "====================" );List < String > subList = list . subList ( 2 , 4 );for ( String str : subList ){System . out . println ( str );}System . out . println ( "====================" );int size = list . size ();for ( int i = 0 ; i < size ; i ++ ){String s = list . get ( i );System . out . println ( s );}System . out . println ( "===================" );ArrayList < Integer > numbers = new ArrayList <> ();numbers . add ( 1 );numbers . add ( 2 );numbers . add ( 3 );numbers . add ( 4 );//移除下标为 3 这个位置的元素numbers . remove ( 3 ); // 这是移除下标为 3 这个位置的元素还是移除 3 这个元素？//移除 3 这个元素numbers . remove (( Integer ) 3 );for ( Integer number : numbers ){System . out . println ( number );}numbers . add ( 2 );numbers . add ( 2 );int index1 = numbers . indexOf ( 2 );int index2 = numbers . lastIndexOf ( 2 );System . out . println ( index1 );System . out . println ( index2 );}}
- ArrayList 继承于 AbstractList ， AbstractList 继承于 AbstractColletion
- ensureCapacityInternal(int minCapacity) 确保数组有足够的容量来存储新添加的数据
- void grow(int minCapacity) 实现数组扩容，扩容至原来的1.5倍
- ListItr 可以从前到后对集合进行遍历，也可以从后往前对集合进行遍历,还可以向集合中添加元素，修改元素。而 Itr 只能从前到后对集合进行遍历。
ArrayList底层采用的是数组来存储元素，根据数组的特性， ArrayList 在随机访问时效率极高，在增加 和删除元素时效率偏低，因为在增加和删除元素时会涉及到数组中元素位置的移动。 ArrayList 在扩容 时每次扩容到原来的 1.5 倍
3. LinkedList
示例及源码解读
单向链表
package com . wq . list ;/*** 自定义单向链表* @param <T> 泛型变量*/public class MyNode < T > {private T data ; // 链中存储的数据private MyNode < T > next ; // 下一个链public MyNode ( T data , MyNode < T > next ) {this . data = data ;this . next = next ;}public T getData () {return data ;}public void setData ( T data ) {this . data = data ;}public MyNode < T > getNext () {return next ;}public void setNext ( MyNode < T > next ) {this . next = next ;}}package com . wq . list ;public class MyNodeTest {public static void main ( String [] args ) {MyNode < String > first = new MyNode <> ( " 第一个链 " , null );MyNode < String > second = new MyNode <> ( " 第二个链 " , null );first . setNext ( second );MyNode < String > third = new MyNode <> ( " 第三个链 " , null );second . setNext ( third );MyNode < String > fourth = new MyNode <> ( " 第四个链 " , null );third . setNext ( fourth );MyNode < String > nextNode = first ;while ( nextNode != null ){System . out . println ( nextNode . getData ());nextNode = nextNode . getNext ();}System . out . println ( "===================" );MyNode < Integer > number4 = new MyNode <> ( 4 , null );MyNode < Integer > number3 = new MyNode <> ( 3 , number4 );MyNode < Integer > number2 = new MyNode <> ( 2 , number3 );MyNode < Integer > number1 = new MyNode <> ( 1 , number2 );MyNode < Integer > next = number1 ;while ( next != null ){System . out . println ( next . getData ());next = next . getNext ();}}}
双向链表
package com . wq . list ;/*** 自定义双向链表* @param <T>*/public class DeNode < T > {private T data ; // 链中存储的数据private DeNode < T > prev ; // 前一个链private DeNode < T > next ; // 后一个链public DeNode ( T data , DeNode < T > prev , DeNode < T > next ) {this . data = data ;this . prev = prev ;this . next = next ;}public T getData () {return data ;}public void setData ( T data ) {this . data = data ;}public DeNode < T > getPrev () {return prev ;}public void setPrev ( DeNode < T > prev ) {this . prev = prev ;}public DeNode < T > getNext () {return next ;}public void setNext ( DeNode < T > next ) {this . next = next ;}}package com . wq . list ;public class DeNodeTest {public static void main ( String [] args ) {DeNode < Integer > number1 = new DeNode <> ( 1 , null , null );DeNode < Integer > number2 = new DeNode <> ( 2 , number1 , null );number1 . setNext ( number2 );DeNode < Integer > number3 = new DeNode <> ( 3 , number2 , null );number2 . setNext ( number3 );DeNode < Integer > number4 = new DeNode <> ( 4 , number3 , null );number3 . setNext ( number4 );DeNode < Integer > nextNode = number1 ;while ( nextNode != null ){System . out . println ( nextNode . getData ());nextNode = nextNode . getNext ();}System . out . println ( "==================" );DeNode < Integer > prevNode = number4 ;while ( prevNode != null ){System . out . println ( prevNode . getData ());prevNode = prevNode . getPrev ();}}}
- LinkedList 继承于 AbstractSequentialList ， AbstractSequentialList 继承于 AbstractList ， AbstractList 继承于 AbstractColletion
- void addFirst(E e) 将数据存储在链表的头部
- void addLast(E e) 将数据存储在链表的尾部
- E removeFirst() 移除链表头部数据
- E removeLast() 移除链表尾部数据
package com . wq . list ;import java . util . LinkedList ;public class LinkedListTest {public static void main ( String [] args ) {LinkedList < String > list = new LinkedList <> ();list . add ( " 第一个字符串 " );list . add ( " 第二个字符串 " );list . addLast ( " 第三个字符串 " );list . addFirst ( " 第四个字符串 " );String first = list . removeFirst (); // 将第一个链移除String last = list . removeLast (); // 将最后一个链移除System . out . println ( first );System . out . println ( last );first = list . getFirst ();last = list . getLast ();System . out . println ( first );System . out . println ( last );}}
LinkedList底层采用的是双向链表来存储数据，根据链表的特性可知， LinkedList 在增加和删除元素时 效率极高，只需要链之间进行衔接即可。在随机访问时效率较低，因为需要从链的一端遍历至链的另一 端。
4. 栈
package com . wq . list ;import java . util . ArrayList ;/*** 自定义栈：后进先出*/public class MyStack < T > extends ArrayList < T > {public void push ( T t ){add ( t );}public T pop (){if ( size () == 0 ) throw new IllegalArgumentException ( " 栈里没有数据啦 " );T t = get ( size () - 1 );remove ( t );return t ;}}package com .wq . list ;public class MyStackTest {public static void main ( String [] args ) {MyStack < Integer > stack = new MyStack <> ();stack . push ( 1 );stack . push ( 2 );stack . push ( 3 );stack . push ( 4 );stack . push ( 5 );while ( ! stack . isEmpty ()){System . out . println ( stack . pop ());}}}
练习
从控制台录入5 位学生信息：姓名，性别，年龄，成绩，并将这些学生信息以 "," 衔接起来，然后存储至文本中。然后再从文本中将这些信息读取至集合中。
package com . wq . list ;import java . io . * ;import java . util . ArrayList ;import java . util . List ;import java . util . Scanner ;/*** 从控制台录入 5 位学生信息：姓名，性别，年龄，成绩，并将这些学生信息以 "," 衔接起来，* 然后存储至文本中。然后再从文本中将这些信息读取至集合中。*/public class Exercise {public static void main ( String [] args ) {List < Student > students = new ArrayList <> ();Scanner sc = new Scanner ( System . in );for ( int i = 0 ; i < 5 ; i ++ ){System . out . println ( " 请输入姓名： " );String name = sc . next ();System . out . println ( " 请输入性别： " );String sex = sc . next ();System . out . println ( " 请输入年龄： " );int age = sc . nextInt ();System . out . println ( " 请输入成绩： " );double score = sc . nextDouble ();students . add ( new Student ( name , sex , age , score ));}saveStudents ( students , "F:\\stu\\stu.txt" );List < Student > read = readStudents ( "F:\\stu\\stu.txt" );for ( Student stu : read ){System . out . println ( stu );}}public static List < Student > readStudents ( String path ){List < Student > students = new ArrayList <> ();try ( FileReader reader = new FileReader ( path );BufferedReader br = new BufferedReader ( reader );){String line ;while (( line = br . readLine ()) != null ){String [] arr = line . split ( "," );//name + "," + sex +"," + age + "," + score;String name = arr [ 0 ];String sex = arr [ 1 ];int age = Integer . parseInt ( arr [ 2 ]); // Float.parseFloat()double score = Double . parseDouble ( arr [ 3 ]);students . add ( new Student ( name , sex , age , score ));}} catch ( FileNotFoundException e ) {e . printStackTrace ();} catch ( IOException e ) {e . printStackTrace ();}return students ;}public static void saveStudents ( List < Student > students , String path ){File file = new File ( path );File parent = file . getParentFile ();if ( ! parent . exists ()) parent . mkdirs ();try ( FileWriter writer = new FileWriter ( file );BufferedWriter bw = new BufferedWriter ( writer );){for ( Student stu : students ){bw . write ( stu . toString ());bw . newLine ();}bw . flush ();} catch ( IOException e ) {e . printStackTrace ();}}}