本练习使用LinkedList处理100,000条数据
从遍历速度上看：
使用index非常慢，应该避免
使用Iterator速度快，但仍不及ArrayList一半速度。
从添加数据（尾部插入）来看，
比ArrayList慢很多，原因是ArrayList后期一次扩容量大。
对于遍历模式，
ArrayList用不用迭代器遍历似乎没区别，多次测试后两者速度，相同或相若。
但参考https://blog.csdn.net/weixin_39148512/article/details/79234817
这篇文章提到不用迭代器会更快？
关于LinkedList详细性能，
可以参考https://www.cnblogs.com/ming-szu/p/9533019.html这篇实验结论：
ming_szu：
“
-
在尾部插入数据，数据量较小时LinkedList比较快，因为ArrayList要频繁扩容，当数据量大时ArrayList比较快，因为ArrayList扩容是当前容量*1.5，大容量扩容一次就能提供很多空间，当ArrayList不需扩容时效率明显比LinkedList高，因为直接数组元素赋值不需new Node
-
在首部插入数据，LinkedList较快，因为LinkedList遍历插入位置花费时间很小，而ArrayList需要将原数组所有元素进行一次System.arraycopy
-
插入位置越往中间，LinkedList效率越低，因为它遍历获取插入位置是从两头往中间搜，index越往中间遍历越久，因此ArrayList的插入效率可能会比LinkedList高
-
插入位置越往后，ArrayList效率越高，因为数组需要复制后移的数据少了，那么System.arraycopy就快了，因此在首部插入数据LinkedList效率比ArrayList高，尾部插入数据ArrayList效率比LinkedList高
”
import java.util.*;
import java.util.regex.*;
/*
* This class is mean to practise data manipulation of LinkedList
*
* LinkedList has high performance for data inserting and removing
* noted that iterator Binary Search could highly improve its searching
* performance
*/
public class LinkedListPrac{
//start system time
private static long start;
public static void main(String[] args){
//1. declare a LinkedList and instantiate it
LinkedList<String> linkedList= new LinkedList<String>();
//2. declare an ArrayList and instantiate it
ArrayList<String> arrayList= new ArrayList<String>();
//3. add 100,000 data to linkedList and count duration
System.out.println("==============3==============");
getListType(linkedList);
start = System.currentTimeMillis();
insertData(linkedList);
countTime(start);
//4.add 100,000 data to arrayList and count duration
//noted that arraylist is much faster while inserting
System.out.println("==============4==============");
getListType(arrayList);
start = System.currentTimeMillis();
insertData(arrayList);
countTime(start);
//5.go through all data,and get the sum
//compare time spent with and without iterator
System.out.println("==============5==============");
getListType(linkedList);
//with index,count time
start = System.currentTimeMillis();
traverseIndex(linkedList);
countTime(start);
//with iterator,count time
start = System.currentTimeMillis();
traverseIterator(linkedList);
countTime(start);
//6. count sum again by using ArrayList
System.out.println("==============6==============");
getListType(arrayList);
//with index,count time
start = System.currentTimeMillis();
traverseIndex(arrayList);
countTime(start);
//with iterator,count time
start = System.currentTimeMillis();
traverseIterator(arrayList);
countTime(start);
//7. remove the first and the last data of linkList
// then print the first and the last data of the new list
System.out.println("==============7==============");
getListType(linkedList);
start = System.currentTimeMillis();
linkedList.removeFirst();
linkedList.removeLast();
System.out.println("first data: "+linkedList.getFirst());
System.out.println("last data: "+linkedList.getLast());
countTime(start);
//8. inserting all data of arraylist into linkedList
//starting after the mid index of the linkedlist
System.out.println("==============8==============");
System.out.println("inserting arraylist data into linkedList...");
start = System.currentTimeMillis();
int insertPos =linkedList.size()>1?linkedList.size()/2:1;
linkedList.addAll(insertPos,arrayList);
countTime(start);
System.out.println("size of new linkedlist is "+linkedList.size()
+" ,and the first and last data is "
+ linkedList.getFirst() + "||"+linkedList.getLast());
//9. get rid of identical data from linkedList
System.out.println("==============9==============");
System.out.println("getting rid of identical data from linkedList...");
start = System.currentTimeMillis();
LinkedHashSet<String> linkedHashSet = new LinkedHashSet<String>(linkedList.size());
linkedHashSet.addAll(linkedList);
linkedList.clear();
linkedList.addAll(linkedHashSet);
countTime(start);
System.out.println("size of new linkedlist is "+linkedList.size()
+" ,and the first and last data is "
+ linkedList.getFirst() + "||"+linkedList.getLast());
}
/*
* insert numbers as String from 1 to 100,000 into a List<String>
*/
public static void insertData(List<String> list){
for (int i=1;i<100001;i++){
list.add(String.valueOf(i));
}
}
/*
* go through the list by index
*/
public static void traverseIndex(List<String> list){
int sum=0;
for (int i=0;i<list.size();i++){
sum+=Integer.parseInt(list.get(i));
}
System.out.println("The sum of all data counted without iterator: "+ sum);
}
/*
* go through the list by iterator
*/
public static void traverseIterator(List<String> list){
int sum=0;
Iterator iterator = list.iterator();
while (iterator.hasNext()){
sum+=Integer.parseInt(iterator.next().toString());
}
System.out.println("The sum of all data counted with iterator: "+ sum);
}
/*
* count time of a process by given start system time
*/
public static void countTime(long start){
long end = System.currentTimeMillis();
long duration = end - start;
System.out.println("Time spent on this process: " + duration +" ms");
}
/*
* get the class name of the list for data access
*/
public static void getListType(List<String> list){
Pattern ptn = Pattern.compile("[A-Z]\\D+");
Matcher mtn = ptn.matcher(list.getClass().getName().trim());
mtn.find();
System.out.println(mtn.group());
}
}
输出结果：
==============3==============
LinkedList
Time spent on this process: 12 ms
==============4==============
ArrayList
Time spent on this process: 7 ms
==============5==============
LinkedList
The sum of all data counted without iterator: 705082704
Time spent on this process: 6753 ms
The sum of all data counted with iterator: 705082704
Time spent on this process: 10 ms
==============6==============
ArrayList
The sum of all data counted without iterator: 705082704
Time spent on this process: 7 ms
The sum of all data counted with iterator: 705082704
Time spent on this process: 5 ms
==============7==============
LinkedList
first data: 2
last data: 99999
Time spent on this process: 5 ms
==============8==============
inserting arraylist data into linkedList...
Time spent on this process: 28 ms
size of new linkedlist is 199998 ,and the first and last data is 2||99999
==============9==============
getting rid of identical data from linkedList...
Time spent on this process: 43 ms
size of new linkedlist is 100000 ,and the first and last data is 2||100000