2021 Niuke written examination summary 02

Niu Kewang written test

This article is the problem of Niuke at the beginning , Tell the truth , Unclear this Point to or new The principle of is not mastered , Basically can't do ; Then there is you, except for meeting Front end and TCP/IP, You have to know java Threads 、 database 、 data structure , Don't talk much , Go straight to the question ！

Threads X Yes wait Method , It will not return because of which operation

1、B Thread calls X Of Join() Method
2、C Threads call shared variables notifyAll()
3、A Threads call shared variables notify()
4、D Thread calls X Of interrupt()

answer ：？

This rookie won't give the answer , Because it's really beyond my ability , Leave reference here , I hope readers can actively leave messages , Actually, I didn't want to write this article , But when I think about it, I still have a little fantasy , I hope readers can actively communicate ！

Reference resources ：wait()、join()、sleep()、yield() and interrupt() Method

InnoDB Transaction isolation level Serializable What problems can be solved

1、 Fantasy reading
2、 It can't be read repeatedly
3、 Dirty reading
4、 All of the above will do

answer ：4
Reference resources ：MySQL Innodb Transaction isolation level

The tree description is wrong

1、 Any node of binary search tree x, All items in the left subtree are less than x, All items in the right subtree are greater than x
2、AVL Tree is the height difference between the left and right subtrees of each node 1 Binary search tree of
3、 According to the preface 、 In the following order , A binary tree can be uniquely identified
4、 The red black tree is AVL A variation of a tree , The height difference between its left and right trees may be greater than 1

answer ：3

1 The reference of ： Binary search tree
2 The reference of ： Search tree -- AVLTree 【 Self-balancing binary search tree 】 Principle diagram and example code

3 The reference of ： front 、 in 、 Whether post order traversal can determine a binary tree ？ reason ？

4 The reference of ： Tree structure series （ Two ）： Balanced binary trees 、AVL Trees 、 Red and black trees

Code running problem 1

function A(x){
    
  this.x = x;
}
A.prototype.x = 1;
function B(x){
    
  this.x = x;
}
B.prototype = new A();
var a = new A(2),b = new B(3);
//console.log(a);
//console.log(b);
delete b.x;
//console.log(b);
console.log(a.x);
console.log(b.x);

answer ：
2
undefined

The rookie suddenly found , It seems that this prototype is only used to influence you , Actually, add something to the prototype , Yes new The instance object has no effect , It's just new These things will be added to the prototype of the example ！

Code running problem 2

var obj = {
    },a = {
    a : 1},b = {
    b : 2},c = {
    c : 3};
obj[a] = 1;
obj[b] = 2;
console.log(obj);
console.log(obj[c]);

answer ：
2

Novices here don't understand very much , We can only rely on readers' active communication .

Code running problem 3

var a = 1;
function Fn1(){
    
  var a = 2;
  //console.log(this);
  //console.log(this.a,a);
  console.log(this.a + a);
}
function Fn2(){
    
  var a = 10;
  //console.log(this);
  Fn1();
}
Fn2();
var Fn3 = function(){
    
  //console.log(this);
  this.a = 3;
}
Fn3.prototype = {
    
  a : 4
}
var fn3 = new Fn3();
Fn1.call(fn3);

answer ：
3
5

This question examines this Pointed question , If a function is not assigned to a variable , So this It points to window, If assigned, it refers to the assigned variable ; and call Will be able to this Point to fn3 example , The prototype chain here also affects you , It won't change a Value ; And that is The variables in each function will not affect each other , If there is one outside , that The inside of the function will cover the outside ！

Part one is about the study of variable scope , Read my blog ： Wechat applet project encountered problem 2 ： Variable scope （ To continue ）| Use data The array in is assigned to the variable b, change b Value , The solution of array change | js The difference between basic types and reference types | Variable naming conflicts