7.7 sheen Xiyin written test

Cast Java Engineer position , The question type is 10 Multi channel single selection +5 There are many ways to choose +1 Algorithm questions +1 Avenue sql topic , Duration 1h

choice question

1.spring The propagation characteristics of things , The wrong is ：

PROPAGATION_REQUIRED: Support current transaction , If there is no current transaction , Throw an exception .

（ Should be ： Support current transaction , If there is no current transaction , Just create a new transaction ）

PROPAGATION_REQUIRED: Support current transaction , If there is no current transaction , Just create a new transaction .

PROPAGATION_SUPPORTS: Support current transaction , If there is no current transaction , Execute as a non transaction .

PROPAGATION_MANDATORY: Support current transaction , If there is no current transaction , Throw an exception .

PROPAGATION_REQUIRES_NEW: New transaction , If there are currently transactions , Suspend current transaction .

PROPAGATION_NOT_SUPPORTED: Perform operations in a non transactional way , If there are currently transactions , Suspend the current transaction .

PROPAGATION_NEVER: To execute in a non transactional manner , If there are currently transactions , Throw an exception .

2. In the following description of linear linked list , The right is ：

When inserting and deleting , There is no need to move the elements in the linked list .

3. The correct description of the following program code is ：

class HasStatic{
    private static int x = 100;
    public static void main(String args[ ]){
        HasStatic hs1 = new HasStatic();
        hs1.x++;
        HasStatic hs2 = new HasStatic();
        hs2.x++;
        hs1=new HasStatic();
        hs1.x++;
        HasStatic.x--;
        System.out.println( "x=" +x);
    }
}

 4. The following does not belong to hash The solution to the collision is ：

Linear detection 、 Single rotation method 、 Second detection 、 Zipper method

5. The system allocates... To a process 4 Page boxes , The page number sequence accessed by this process is 2,0,2,9,3,4,2,8,2,4,8,4,5. If the page number of the next page visited is 7, basis LRU Algorithm , The page number of the page to be eliminated is ：

2

6. process P1 and P2, resources A and B, The process operation on resources is defined as follows ： Read resources A：rA; Read resources B：rB; Write resources A：wA; Write resources B：wB. At the same time, it stipulates , Before the process reads a resource , A shared lock must be added , An exclusive lock must be added before writing a resource ; When a resource is shared by a process , It can be shared by other processes , But you can't add an exclusive lock ; Resources are locked exclusively by processes , Other processes cannot be locked . Release the lock after the process completes all operations . process P1 And processes P2 Concurrent execution , Which of the following running sequences may deadlock _____.

Four necessary conditions for deadlock ：

Resources are exclusive 、 Inalienable 、 Request and maintain 、 Loop waiting for .

7. Judge var1.intValue() Such output results

8. The following about HTTP/2 The description of is wrong ：

D Describe the HTTPS

9. mysql The database has a course selection table learn(student_id int,course_id int), The fields represent student number and course number respectively , Now I want to get the number of courses selected by each student , May I ask the following sql The correct statement is ( )

10. Which of the following data structures is a nonlinear structure ？

The linear table 、 queue 、 Binary tree 、 Stack

11. solve hash Conflicting methods are described incorrectly ？

D 

12. About the following code , The following statement is correct ： ( ) 

public class Test {
private synchronized void a() {
}
private void b() {
synchronized (this) {
}
}
private synchronized static void c() {
}
private void d() {
synchronized (Test.class) {
}
}
}

AC 

Modify non static methods Locked this object ;    Modified static method Locked class object

13. Which of the following sql Statement query can make better use of index

14. Two threads execute the following code concurrently , hypothesis a Global variable , So the following output ___ Which is possible ?

int a=1;
void foo(){
    ++a;
    printf("%d", a);
}

32 23 33 22 It's possible

15.JDK17 Which of the following features are included ？

Algorithm problem

String decoding

lc The original title is Auxiliary stack method

class Solution {
    public String decodeString(String s) {
        StringBuilder res = new StringBuilder();
        int multi = 0;
        LinkedList<Integer> stack_multi = new LinkedList<>();
        LinkedList<String> stack_res = new LinkedList<>();
        for(Character c : s.toCharArray()) {
            if(c == '[') {
                stack_multi.addLast(multi);
                stack_res.addLast(res.toString());
                multi = 0;
                res = new StringBuilder();
            }
            else if(c == ']') {
                StringBuilder tmp = new StringBuilder();
                int cur_multi = stack_multi.removeLast();
                for(int i = 0; i < cur_multi; i++) tmp.append(res);
                res = new StringBuilder(stack_res.removeLast() + tmp);
            }
            else if(c >= '0' && c <= '9') multi = multi * 10 + Integer.parseInt(c + "");
            else res.append(c);
        }
        return res.toString();
    }
}

Mysql

Some question and answer 11 Monthly and daily responses per capita

There is a question and answer creator's answer table answer_tb as follows （ among answer_date Indicates the creation date 、author_id Refers to the creator number 、issue_id Express problem id、char_len Indicates the number of words in the answer ）：

Please make statistics 11 Monthly and daily responses per capita （ Number of questions answered / The number of respondents ）, Sort by answer date , Two decimal places are reserved for the result , The output of the above example is as follows ：

select answer_date,
       round(count(issue_id)/count(DISTINCT author_id),2) per_num
from answer_tb
where month(answer_date) = 11
group by answer_date

select answer_date, round(count(*)/count(distinct author_id), 2) 
from answer_tb 
group by answer_date 
order by answer_date;