❤️ Is the collection simple? Are you kidding? Liver for a week, is the essence, all words to explain! Interview is no longer afraid of questions!!! ❤️

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Many interview articles have been sorted out in front, and the feedback from the little partner is excellent:

1,❤️ liver failure! Sorted out the spring interview [including answers] for a week and hanged the Java interviewer [suggestions collection]! ❤️

2,❤️ When the liver is over, master the data structure and algorithm one day, interview questions, hang the interviewer, and suggest collecting ❤️

So brother Meng got excited and dried three bottles of Red Bull. I gave up shopping with my girlfriend on Tanabata and wrote a collection of interview dry goods. I don't talk about dry goods directly.


Q1: say ArrayList

Q2: say LinkedList  

  Q3: the difference between ArrayList and linklist

Q4: what are the features and implementations of set?

Q5: what are the characteristics of treemap?

Q6: what are the characteristics of HashMap?

Q7: why is HashMap thread unsafe?

Q8: tell me about your understanding of haspmap【 [key, key]

Q9: difference between HashMap and hashtable


Q1: say ArrayList

ArrayList is a thread safe list with variable capacity, which enables the implementation of array. When the collection is expanded, a more array will be created and the original array will be copied to the new array. ⽀ hold fast random access to elements, but the insertion and deletion speed is very slow. ArrayList implements randomaccess tag concatenation. If ⼀ classes implement this concatenation, it means that ⽤ index traversal ⽐ iterator is faster.

Elementdata is the data field of ArrayList. It is modified by transient. When serializing, it will call "writeobject" to write the stream. When deserializing, it will call "readObject" to reassign to the elementdata of the new object. The reason is that the capacity of elementdata is usually equal to the number of actual storage elements, so only the array elements with actual values need to be sent. Size is the current actual size, and elementdata ⼤⼩⼤ is equal to size.

Modcount records the number of structural changes in ArrayList and inherits ⾃ abstractlist. All ⽅ methods involving structural changes will increase this value. Expectedmodcount is the modcount value recorded during the initialization of the iterator. Each time a new element is accessed, it will be checked whether the modcount and expectedmodcount are equal. If they are not equal, an exception will be thrown. This mechanism is called fail fast, and all collection classes have this mechanism.

Q2: say LinkedList

LinkedList is essentially a two-way linked list. Compared with ArrayList, LinkedList can insert and delete faster, but random access to elements is very slow. In addition to inheriting abstractlist, it also implements the deque connection, which has the properties of queue and stack. Member variables are modified by transient, and the principle is similar to ArrayList.

LinkedList contains three important members: size, first, and last. Size is the number of nodes in the bidirectional linked list, and "RST" and "last" refer to the "tail" node respectively.

LinkedList     The utility model has the advantages that scattered memory units can be associated by adding references to form a linear structure for searching in link order, and the memory profit rate is low.

Q3: the difference between ArrayList and linklist

Take a look at a simple code of ArrayList and linklist. You can take a look at it yourself;

public ArrayList(int initialCapacity) {
     if (initialCapacity > 0) {
         this.elementData = new Object[initialCapacity];
    }  else if (initialCapacity == 0) {
         this.elementData = EMPTY_ ELEMENTDATA;
    }  else {
         throw new IllegalArgumentException("Illegal Capacity: "+

 *  Constructs an empty list with an initial capacity of ten.
public ArrayList() {

 *  Constructs a list containing the elements of the specified
 *  collection, in the order they are returned by the collection's
 *  iterator.
 * @ param c the collection whose elements are to be placed into this list
 * @ throws NullPointerException if the specified collection is null
public ArrayList(Collection<?  extends E> c) {
     elementData = c.toArray();
     if ((size = elementData.length) !=  0) {
        //  c.toArray might (incorrectly) not return Object[] (see 6260652)
         if (elementData.getClass() !=  Object[].class)
             elementData = Arrays.copyOf(elementData, size, Object[].class);
    }  else {
        //  replace with empty array.
         this.elementData = EMPTY_ ELEMENTDATA;

 *  Trims the capacity of this <tt>ArrayList</tt> instance to be the
 *  list's current size.    An application can use this operation to minimize
 *  the storage of an <tt>ArrayList</tt> instance.
public void trimToSize() {
     if (size < elementData.length) {
         elementData = (size == 0)
          :  Arrays.copyOf(elementData, size);

Class inheritance diagram relationship:


public class LinkedList<E> extends AbstractSequentialList<E> implements

List<E>, Deque<E>, Cloneable, java.io.Serializable {}

Class inheritance diagram relationship:

Data structure implementation: ArrayList is the data structure implementation of dynamic array, and LinkedList is the data structure implementation of bidirectional linked list.

Random access efficiency: ArrayList is more efficient than LinkedList in random access. Because LinkedList is a linear data storage method, you need to move the pointer to find it from front to back.

Addition and deletion efficiency: LinkedList is more efficient than ArrayList in non head and tail addition and deletion operations, because ArrayList addition and deletion operations affect the subscripts of other data in the array.

Generally speaking, ArrayList is more recommended when the elements in the collection need to be read frequently, and LinkedList is more recommended when there are many insert and delete operations.

1. Whether thread safety is guaranteed: ArrayList and LinkedList are not synchronized, that is, thread safety is not guaranteed;

2. Underlying data structure: ArrayList uses an object array at the bottom; The underlying LinkedList uses a two-way linked list data structure (before JDK1.6, it was a circular linked list, and jdk1.7 cancels the cycle. Pay attention to the difference between bidirectional linked list and bidirectional circular linked list, which is introduced below!)

3. Whether insertion and deletion are affected by element location: ① ArrayList is stored in array, so the time complexity of inserting and deleting elements is affected by element location. For example, when the add (E) method is executed, the ArrayList will append the specified element to the end of the list by default. In this case, the time complexity is O (1). However, if you want to insert and delete elements at the specified position I, the time complexity of (add (int index, e element)) is O (n-i). Because when performing the above operations, the (n-i) elements after the I and I elements in the set must perform the operation of moving backward / forward one bit. ② The LinkedList is stored in a linked list. Therefore, for the insertion of the add (E, e) method, the time complexity of deleting elements is not affected by the element position, which is approximately o (1). If you want to insert and delete elements at the specified position I ((add (int index, e element)) the time complexity should be o (n)) because a new linked list needs to be created, Copy the first I-1 elements and add a new element in position I, and finally attach n-i elements.

4. Whether it supports fast random access: LinkedList does not support efficient random element access, while ArrayList does. Fast random access is to quickly obtain the element object (corresponding to the get (int index) method) through the element sequence number.

5. Memory space occupation: the space waste of ArrayList is mainly reflected in that a certain capacity space is reserved at the end of the list, while the space cost of LinkedList is reflected in that each element needs to consume more space than ArrayList (because it needs to store direct successors, direct precursors and data).

Q4: what are the features and implementations of set?

Set does not allow elements to be repeated and ordered. It often implements HashSet, linkedhashset and TreeSet.
HashSet is implemented through HashMap. The key of HashMap is the element stored in HashSet. All keys make ⽤ the same value and ⼀ object type constants named present. Make ⽤ key ensure element uniqueness, but not order. Because HashSet is implemented by HashMap, thread is not safe.

When HashSet judges whether the elements are the same, it directly compares the packing type by the value ⽐. For the reference type, first compare whether the hashcode is the same. If it is different, it means that it is not the same object. If it is the same, continue to compare equals. If it is the same, it is the same object.
Linkedhashset inherits ⾃ HashSet and is implemented through LinkedHashMap to maintain the element insertion order of ⽤ two-way linked list.
TreeSet is implemented through treemap. When adding elements to the set, insert them into the appropriate position according to the ⽐ comparison rules to ensure that the inserted set is still orderly.


Q5: what are the characteristics of treemap?


Treemap is implemented based on the "red" tree. The average and worst time complexity of adding, deleting, modifying and querying are o (logn), and the most characteristic is that the keys are orderly.

The key must implement the comparable connector or the provided comparator comparator, so the key cannot be null.
HashMap relies on hashcode and equals for de duplication, and treemap relies on comparable or comparator.
During treemap sorting, if the comparator is not empty, the compare method of the comparator will be used first, otherwise the key will be implemented.
Comparable's CompareTo ⽅ method, both of which are dissatisfied with ⾜ will throw an exception. Treemap adds and deletes tree nodes through put and deleteentry. There are three rules for inserting new nodes: ① new nodes to be adjusted are always red. ② If the "node" of the new node is "12270", it does not need to be adjusted. ③ If the ⽗ node inserted into the new node is red, because the red tree cannot have adjacent red ⾊, enter the ⼊ cycle judgment and adjust it by re landing or rotating left and right. The interpolation operation of treemap is to traverse down according to the key pair, find the node value to the right, and find the node value to the left. First, operate according to the characteristics of the cross search tree, and then re rotate and rotate to maintain the characteristics of the red tree.

Q6: what are the characteristics of HashMap?

Before jdk8, the underlying implementation was array + linked list. Jdk8 was changed to array + linked list / red "tree, and the node type was changed from entry to node. The main member variables include the table array storing data, the number of elements, size, and the loading factor ⼦ LoadFactor.

The table array records the data of HashMap. Each subscript corresponds to a linked list. All hash conflicting data will be stored in the same linked list. The node / entry node contains four member variables: key, value, next pointer and hash value.

The data in HashMap exists in the form of key value pairs. The hash value corresponding to the key is used to calculate the array subscript. If the hash value of the two element keys is similar, a hash conflict will occur and they will be placed on the same linked list. In order to make the query efficiency as efficient as possible, the hash value of the key should be dispersed as much as possible.

The default initialization capacity of HashMap is 16, the expansion capacity must be the power of 2, the maximum capacity is 1 < < 30, and the default loading reason is

Q7: why is HashMap thread unsafe?

Everyone should know that HashMap is not thread safe. Specific problem scenarios include:

one      Data loss
two      Data duplication
three      Dead cycle

As for the problem of dead loop, I think it doesn't exist in Java 8. In versions before Java 8, dead loop occurs because the linked list is processed in reverse order in the process of resize; In Java 8, there is no reverse order processing, and naturally there will be no dead loop.  

The great God once explained this:

Through the above source code in Java 7, analyze why data loss occurs. If two threads execute the statement table [i] = null at the same time, both threads will create an entry in the storage area, so data loss will occur. If two threads find that their keys do not exist at the same time, and the keys of the two threads are actually the same, when writing to the linked list, the first thread sets e as its own entry, while the second thread executes e.next. At this time, it gets the last node and will still insert the data it holds into the linked list, resulting in data duplication. Through the commodity put source code, we can find that we first write the data into the map, and then decide whether to resize according to the number of elements. There will be a more strange loop in the resizing process. This is mainly because HashMap reverses the linked list during resize. Suppose two threads resize at the same time, a - > B. the first thread is relatively slow in processing, and the second thread has completed the reverse order programming of B-A, then there is a loop, B - > A - > B. in this way, there will be a surge in CPU utilization. In the afternoon, I suddenly received an alarm of insufficient CPU utilization of one of the machines. Through jstag content analysis, it was found that there may be dead circulation and data loss. Of course, there are also problems with the operation of linked list. PS: in this process, it can be found that the reason for the occurrence of dead loop mainly lies in the reverse order processing of linked list. In Java 8, the reverse order list is no longer used, and the dead loop problem has been greatly improved.  

The thread insecurity of HashMap is mainly reflected in the following two aspects:

1. In jdk1.7, when capacity expansion is performed concurrently, ring chain and data loss will be caused.
2. In JDK1.8, data coverage occurs during concurrent put operations.

Q8: tell me about your understanding of haspmap【 [key, key]

First of all, we all know that HashMap is a set, a set of < key and value >, and each node has a key and value. The specific reference code is as follows:

static class Node<K,V> implements Map.Entry<K,V> {
    final int hash;
    final K key;
    V value;
    Node<K,V> next;

The array structure of HashMap is array + (linked list or red black tree)

Why use this structure to store elements? First, we have to analyze the characteristics of the following arrays and linked lists:

Array: high query efficiency, low insertion and deletion efficiency.

Linked list: low query efficiency and high insertion and deletion efficiency.

At the bottom of HashMap, the structure of array plus (linked list or red black tree) perfectly solves the problem of array and linked list, making the efficiency of query, insertion and deletion very high.

Inheritance diagram of HashMap:


Before jdk8, hash: calculates the hash value of the element key

① When processing the string type, call the stringhash32 method to get the hash value.
② When processing other types of data, provide a random value hashseed that is unique and unchanged relative to the HashMap instance as the initial calculation quantity.
③ XOR and unsigned right shift make hash values more discrete and reduce hash collision probability.
Indexfor: calculated element subscript
And the hash value and array length - 1 to ensure that the result will not exceed the range of table array.

You can refer to the code to see the explanation, and then you will understand it. We can simply summarize the HashMap:

Out of order, null allowed, asynchronous;
The bottom layer is realized by hash table;

The initial capacity and loading factor have a great impact on HashMap. It's not good to set it small, and it's not good to set it large.
Resize: expansion array

① If the current capacity reaches the maximum capacity, set the threshold value to integer maximum, and then the capacity expansion will not be triggered.
② Otherwise, calculate the new capacity and set the threshold to the smaller value of newcapacity x LoadFactor and maximum capacity + 1.
③ Create an entry array with a capacity of newcapacity, and call the transfer method to transfer the elements of the old array to the new array.
Transfer: transfer elements
① Traverse all elements of the old array, call the rehash method to determine whether hash reconstruction is required, and recalculate the hash value of the element key if necessary.
② Call the indexfor method to calculate the subscript I stored in the element, and use the header interpolation method to transfer the elements of the old array to the new array.
Hash: calculates the hash value of the element key
If the key is null, 0 will be returned. Otherwise, the return value of the hashcode method of the key will be 16 bits high and low exclusive or, so that as many bits as possible can participate in the operation, so as to make the distribution of 0 and 1 of the result more uniform and reduce the hash conflict probability.

Put: add element

public V put(K key, V value) {
     return putVal(hash(key), key, value, false, true);
final V putVal(int hash, K key, V value, boolean onlyIfAbsent,
                boolean evict) {
     Node<K,V>[] tab;  Node<K,V> p;  int n, i;
     if ((tab = table) == null || (n = tab.length) == 0)
         n = (tab = resize()).length;
     if ((p = tab[i = (n - 1) & hash]) == null)
         tab[i] = newNode(hash, key, value, null);
     else {
         Node<K,V> e;  K k;
         if (p.hash == hash &&
            (( k = p.key) == key || (key !=  null && key.equals(k))))
             e = p;
         else if (p instanceof TreeNode)
             e = ((TreeNode<K,V>)p).putTreeVal(this, tab, hash, key, value);
         else {
             for (int binCount = 0; ; ++ binCount) {
                 if ((e = p.next) == null) {
                     p.next = newNode(hash, key, value, null);
                     if (binCount >= TREEIFY_ THRESHOLD - 1) // -1 for 1st
                         treeifyBin(tab, hash);
                 if (e.hash == hash &&
                    (( k = e.key) == key || (key !=  null && key.equals(k))))
                 p = e;
         if (e !=  null) { // existing mapping for key
             V oldValue = e.value;
             if (! onlyIfAbsent || oldValue == null)
                 e.value = value;
             return oldValue;
    ++ modCount;
     if (++size > threshold)
     return null;

Let's analyze the implementation method

① Call the putval method to add an element.
② If the table is empty or the length is 0, the capacity will be expanded. Otherwise, the subscript position of the element will be calculated. If it does not exist, newnode will be called to create a node.
③ If it exists and is a linked list, if the hash and key of the first node and the element to be inserted are the same, update the value of the node.
④ If the first node is of treenode type, call puttreeval method to add a tree node. Each time, compare the size of the inserted node and the current node. When the inserted node is small, look for the left subtree, otherwise look for the right subtree. After finding the vacancy, execute two methods: balanceinsert method, insert the node and adjust the balance, and moveroottofront method, Since the root node may change after balancing, you need to reset the root node.
⑤ If they are not satisfied, traverse the linked list, judge whether it is repeated according to the hash and key, and decide whether to update the value or add a new node. If you traverse to the end of the linked list, add nodes. If you reach the tree building threshold 7, you also need to call treeifybin to reconstruct the linked list into a red black tree.
⑥ After storing the element, add 1 to modcount. If + + size > threshold, call resize to expand the capacity.
Get: get the value of the element

public V get(Object key) {
     Node<K,V> e;
     return (e = getNode(hash(key), key)) == null ?  null : e.value;

 *  Implements Map.get and related methods.
 * @ param hash hash for key
 * @ param key the key
 * @ return the node, or null if none
final Node<K,V> getNode(int hash, Object key) {
     Node<K,V>[] tab;  Node<K,V> first, e;  int n;  K k;
     if ((tab = table) !=  null && (n = tab.length) > 0 &&
        ( first = tab[(n - 1) & hash]) !=  null) {
         if (first.hash == hash && // always check first node
            (( k = first.key) == key || (key !=  null && key.equals(k))))
             return first;
         if ((e = first.next) !=  null) {
             if (first instanceof TreeNode)
                 return ((TreeNode<K,V>)first).getTreeNode(hash, key);
             do {
                 if (e.hash == hash &&
                    (( k = e.key) == key || (key !=  null && key.equals(k))))
                     return e;
            }  while ((e = e.next) !=  null);
     return null;

Let's explain the above code:

① Call the getNode method to obtain the node node. If it is not null, return its value value; otherwise, return null.
② In the getNode method, if the array is not empty and there are elements, first compare the hash and key of the first node and the element to be found. If they are the same, they will be returned directly.
③ If the second node is of treenode type, call the gettreenode method to find it. Otherwise, traverse the linked list and find it according to hash and key. If it is not found, it returns null.
Resize: expansion array
Re plan the length and threshold. If the length changes, some data nodes will also be rearranged.
Rescheduling length
① If the current capacity oldcap > 0 and reaches the maximum capacity, set the threshold value to integer maximum value and return to terminate the capacity expansion.
② If the maximum capacity is not reached, when oldcap < < 1 does not exceed the maximum capacity, it will be expanded to twice.
③ If neither is satisfied and the current capacity expansion threshold oldthr > 0, the current capacity expansion threshold is used as the new capacity.
④ Otherwise, set the new capacity to the default initial capacity of 16 and the new capacity expansion threshold to 12.
Rearrange data nodes
① If the node is null, it will not be processed.
② If the node is not null and there is no next node, the hash value of the node and the new capacity - 1 are used to calculate the subscript and store it in the new table array.
③ If the node is of treenode type, call the split method for processing. If the number of nodes HC reaches 6, call the untreeify method to return to the linked list.
④ If it is a linked list node, you need to split the linked list into a linked list whose hash value exceeds the old capacity and a linked list whose hash value does not exceed the capacity. The part with hash & oldcap = = 0 does not need to be processed, otherwise it needs to be placed at the new subscript position. The new subscript = old subscript + old capacity.

Q9: difference between HashMap and hashtable

From the above, we can see the difference between HashMap and hashtable. Xiao Meng has sorted out a table for you. Let's take a general look at it:



Thread unsafe

Null keys and values are allowed

A little more efficient

Method is not synchronized. To provide external synchronization

There are containsvalue and containskey methods

HashMap It is an implementation of map interface introduced by Java 1.2

HashMapIs a lightweight implementation of hashtable


Thread safety

Null keys and values are not allowed

Slightly inefficient

The method is synchronize

With containsmethod

Hashtable Inherits from the dictionary class

Hashtable Older than HashMap

reference resources: https://www.zhihu.com/question/28516433  

Well, after finishing the spring interview, the partners point praise, collection and comments, and walk up three times with one button. See you next time~~


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This course 0 is a basic introduction, from process, thread and JVMopenAt the beginning, each chapter only focuses on one knowledge point, and each chapter has code examples</ span></p> <p style="color: #008781; background: white;">< span style="color: #000000;"> </ span></p> <p style="color: #008781; background: white;">< span style="color: #337fe5;">【 The course is divided into basic part, advanced part and advanced part] < / span ></p> <p style="color: #008781; background: white;">< span style="color: #337fe5;"> 1、 Fundamentals < br / > < / span ></p> <p style="color: #008781; background: white;">< span style="color: #000000;"> The basic part starts with the rotation training of process and thread, memory and CPU time slice, including three thread creation methods, visual observation thread, join, sleep, yield, interrupt, synchronized, reentry lock, object lock, class lock, wait, notify, thread context switching, guard thread, blocking security queue, etc</ span></p> <p style="color: #008781; background: white;">< span style="color: #337fe5;"> 2、 Advanced level < / span ></p> <p style="color: #008781; background: white;">< span style="color: #000000;"> The advanced course covers volatile keywords, actomic classes, visibility, atomicity, ThreadLocal, unsafe bottom layer, synchronous class container, concurrent class container, five kinds of concurrent queues, cow container, inheritablethreadlocal source code analysis, etc</ span></p> <p style="color: #008781; background: white;">< span style="color: #337fe5;"> 3、 Mastery < / span ></p> <p style="color: #008781; background: white;">< span style="color: #000000;"> This course covers the core tools under JUC, such as countdownlath, cyclicbarrier, phaser, semaphore, exchange, reentrantlock, reentrantreadwritelock, stampedlock, locksupport, AQS bottom layer, pessimistic lock, optimistic lock, spin lock, fair lock, unfair lock, exclusive lock, shared lock, reentry lock, thread pool, cachedthreadpool, fixedthreadpool Scheduledthreadpool, singlethreadexecution, custom thread pool, threadfactory, thread pool aspect programming, thread pool dynamic management, high concurrency design mode, future mode, master worker mode, completionservice, forkjoin, etc. < / span ></p> <p style="color: #008781; background: white;">< span style="color: #337fe5;"> The course also includes < / span ></p> <p style="color: #008781; background: white;">< span style="color: #000000;"> Disruptor high concurrency lockless frameworkexplain: disruptor supports 6 million orders per second. Go deep into the underlying principles andopenHair mode, so that you can understand and use</ span></p> <p style="color: #008781; background: white;">< span style="color: #000000;"> High concurrent access limitexplain: it covers barrel algorithm, token barrel algorithm and Google ratelimiter current limitingopenActual combat of Apache JMeter stress test</ span></p> <p> </p> <p class="ql-long-24357476" style="color: #222226; font-family: "font-size:14px; background-color: #ffffff;">< strong><span style="color: #337fe5;">【 What level will I reach after learning?]</ span></strong></p> <p class="ql-long-24357476" style="color: #222226; font-family: "font-size:14px; background-color: #ffffff;">< span style="color: #000000; font-family: ";"> 1. Hang all written test questions related to concurrent programminginterviewQuestion</ span></p> <p class="ql-long-24357476" style="color: #222226; font-family: "font-size:14px; background-color: #ffffff;">< span style="color: #000000; font-family: ";"> 2. Refactor your own system knowledge of concurrent programming, NoagainTalk about concurrent color change</ span></p> <p class="ql-long-24357476" style="color: #222226; font-family: "font-size:14px; background-color: #ffffff;">< span style="color: #000000; font-family: ";"> 3. Accurate mastery < / span > < span style = "color: #000000; font-family: ";"> JAVA</span><span style="color: #000000; font-family: ";"> The principle and use of various concurrent tool classes, methods and keywords</ span></p> <p class="ql-long-24357476" style="color: #222226; font-family: "font-size:14px; background-color: #ffffff;">< span style="color: #000000; font-family: ";"> 4. Easily write more efficient and elegant concurrent programs, and can put forward more solutions in work</ span></p> <p class="MsoNoSpacing" style="margin-left: 18pt; text-indent: -18pt;">< span style="color: #000000;"> </ span></p> <p class="MsoListParagraph" style="margin-left: 18.0pt; text-indent: -18.0pt;"> </ p> <p> </p> <p class="ql-long-24357476" style="color: #008781;"> </ p> <p class="MsoListParagraph" style="color: #008781; margin-left: 36pt; text-indent: -36pt;" align="left"><strong><span style="color: #337fe5;">【</ span><span style="color: #337fe5;"> Crowd oriented < / span > < span style = "color: #337fe5;" >]</ span></strong></p> <p class="MsoListParagraph" style="color: #008781; margin-left: 36pt; text-indent: -36pt;" align="left"><span style="color: #000000;"> 1. Total sense concurrent programmingveryDifficultveryPeople who are complex and dare not learn</ span></p> <p class="MsoListParagraph" style="color: #008781; margin-left: 36pt; text-indent: -36pt;" align="left"><span style="color: #000000;"> 2. Programmers who are ready to change jobs, find jobs and get high salaries</ span></p> <p class="MsoListParagraph" style="color: #008781; margin-left: 36pt; text-indent: -36pt;" align="left"><span style="color: #000000;"> 3. I hope to improve my programming ability,openPeople who deliver more efficient and powerful systems</ span></p> <p class="MsoListParagraph" style="color: #008781; margin-left: 36pt; text-indent: -36pt;" align="left"><span style="color: #000000;"> 4. People who want to master concurrent programming quickly, systematically and accurately</ span></p> <p class="MsoListParagraph" style="color: #008781; margin-left: 18pt; text-indent: -18pt;">< Strong > [curriculum knowledge system chart] < / strong ></p> <p class="MsoListParagraph" style="color: #008781; margin-left: 18pt; text-indent: -18pt;">< img src=" https://img-bss.csdnimg.cn/202007100721287398.png " alt="" /></p>
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