2020 spring new interview! Today's headlines Android interview questions and answers (has got the offer)

Interview Time : 2019.12.29 surface 1-3, 4-6 face 2020.1.03, 2020.1.06 HR face

+ Post interview department : commercialization - Advanced Android Development Engineer

Interview feelings : overall surface was more tired, basic surface, intersecting faces, Boss face, back and forth six docking interviewer (from original to me that the 3 + HR face look a bit like the difference between far ¬_¬). Boss algorithm to face are still writing, but fortunately the interviewer did not embarrass me (honest account of how the algorithm is not ready, hey ...), the algorithm is not too difficult. Overall project is much more than the base asked.

Interview Advice : algorithm, the foundation is the key to getting the project is the touchstone, a good image of the interview is to add sub-item.

Items listed on your resume think more, why do this project? What to do this project aims? What is my solution is? What are my other options relative advantages of the program? What benefits of the project is? Chart of whether the project can be drawn? The main principle in the framework of the project are using the Ins and Outs clear? (I probably saved his own project, grounding a little hasty T ^ T).

If the interview is live or video, the image of a good interview is quite necessary. When the surface of the TL sector, I would mention is relatively a lot of other interviewers relatively little is good, the people's image of the state is better, do not make people feel very tired.

[ 1 face - face basis ]

When you develop Android, for px UI draft is how adaptable?

Android is now stable and efficient adaptation of the UI program , headlines screen adaptation scheme AndroidAutoSize today , headlines today - density value by reflecting the correction system

dpi: screen density, refers to the system software the number of pixels specified unit size, it is often a fixed value is written in the factory system configuration file;

ppi: is the screen pixel density, but this is a physical concept, it will not change objective reality. dpi is the software upon reference to the physical pixel density value of a manually specified, thus ensuring that the physical pixel density within a certain interval use the same value in the software;

dp plus adaptive layout and weight distribution ratio can solve 90 percent of the adaptation problems . Because not all are 480 dpi 1080P phones, such as Google's Pixel2 (1920 * 1080) is of 420 dpi;

Width and height qualifier adaptation: the width and height of all the pixel values to be exhaustive Android mobile phone market, set a reference resolution, other resolutions are calculated according to the reference resolution, in different sizes inside the folders, in accordance with write the corresponding dimens file size. But it has a fatal flaw, it is required to accurately hit adaptation, App package volume also become large

Integer value equal to two objects, == determine whether or not equal?
Jump Activity A Activity B, Activity B press the back key to back to back, each of the two processes lifecycle
Whether the child thread can context.startActivity () (such as ApplicationContext), will not be a problem?

Write demo next test is possible. But what would the problem have yet to understand ...

Handler mechanism of the overall process; Looper.loop () Why not block the main thread; IdHandler (leisure mechanism); postDelay () concrete realization; post () and sendMessage () difference; use Handler requires attention to the problem, how to solve ?

The problem is very small, can prepare a detailed and more ready and more detailed. Handler people own a set of packages to avoid memory leaks

When Native, H5, RN mixed page jump clear how the page stack bridge to achieve?

A project of their own, clear principles on the line, it is unclear about drawing

How to calculate the percentage of a View section visible on the screen?
ClassLoader parents delegate mechanism -
Under the principle of brief Https
What would cause a memory leak, how to fix?
Download a big map, how to ensure not oom? -
I have not done to optimize the UI, and did what?

Debug GPU overdraw, will reduce Overdraw to within reasonable limits;

Reducing the number of nesting levels and controls, in tree view flat as possible (using Hierarchy Viewer can easily view), while removing all unnecessary rendering view;

GPU rendering tools use configuration, precise positioning of the code TraceView positioning problems which occur in specific steps to use;

Use labels, merge reduce nesting level, viewStub lazy initialization, include reuse layout (used in conjunction with the merge)

WebView and JS interactively, shouldOverrideUrlLoading, onJsPrompt use what's the difference -
Flutter, Kotlin used without the contact
Other project-related issues
Algorithm - binary output node element level k

[ 2 surface - Special items ]

Native, H5, when mixed RN jump page, clear page stack to achieve bridge
Page design and difficulty of mixed framework
Design RN universal container
User behavior monitoring program design
JS error control scheme
RN page JS error monitoring and management of user behavior in question find any harvest, optimization points
US group RN RN with respect to the native What are the advantages

[ 3 surface - deeper foundation ]

Picasso your company has not been used to introduce the next
Picasso single-engine, multi-Bundle in the case of how to ensure data isolation?
The difference between the US group RN with Picasso

4. omitted a number of project-related issues ...

How to track page Buried implemented RN
US Mission Home page whether RN, MTFlexBox principle
synchronized static modification method, ordinary methods, classes, methods chunk distinguishing
synchronized principle underlying implementation
volatile role and principles
A modified volatile int variables, multi-threaded to operate i ++, whether or not thread safe? How to ensure i ++ thread-safe? AtomicInteger underlying implementation principle?

Use AtomicInteger can i ++ thread-safe

Understanding of the thread pool at that as well as several key parameters to create a thread pool
Handler mechanism asked again ...
Binder introduce mechanisms, what is the difference and memory sharing mechanism?
Java collections, introduced to the ArrayList and HashMap usage scenarios, the principle underlying implementation
The difference between ArrayList and LinkedList
Algorithm - to merge the two ordered list of
Algorithm - enter a string (. * And free), regular (The letters, *, and any combination thereof), it is determined whether the string legitimate
Under a brief introduction, a number of technical difficulties encountered in the project

[ 4 plane - intersecting face ]

The following code, str final value is how much? Integer value is changed and how much, will be changed?

Test sites : Java value passed (the same question 2). Coding test, modify the parameters in the ChangeValue () method, and does not change the value before;

Principle : the Java programming language always uses call by value , obtained by the method is a copy of all parameter values, that method can not be modified deliver it to the content of any parameter variables. The basic type parameter is a parameter passed a copy of the object type parameter is passed a copy of the address of the object;

Solution to a problem : in changeValue (), for the object type parameter is modified directly address a copy of the target value, the address before the variable has not been modified! If the modified value is an instance of an object inside, before the variable will be modified

  public void test() {
      String str = "123";
      changeValue(str); 
      System.out.println("str值为: " + str);  // str未被改变，str = "123"
  }

  public changeValue(String str) {
      str = "abc";
  }

The following code, again using the object if student needs sentenced empty?

The use of Java method parameters are summarized:

A method can not modify a basic data type of the parameter (i.e., numeric or Boolean);

A method can change the state of a parameter of the object;

A method does not make reference to a new object parameter object

  public void test()  {
      Student student = new Student("Bobo", 15);
      changeValue1(student);   // student值未改变，不为null! 输出结果 student值为 name:Bobo、age:15
      // changeValue2(student);  // student值被改变，输出结果 student值为 name:Lily、age:20
      System.out.println("student值为 name: " + student.name + "、age:" + student.age);
 }

  public changeValue1(Student student) {
      student = null;
  }

  public static void changeValue2(Student student)  {    
       student.name = "Lily";    
       student.age = 20;
  }

Several Java reference type, usage scenarios weak references?
Thread pool classification, explain a few core parameters?
What APK packaging process?

aapt tools packaged resource file, the file is generated R.java

aidl AIDL processing tool file, generate the corresponding .java files

javac tool to compile Java files, generate the corresponding .class file

The converted files into .class Davik VM support .dex file

apkbuilder tool package generated unsigned .apk file

jarsigner to unsigned .apk file is signed

zipalign tool .apk file signature in the alignment process

Why APK to sign? Whether to find out about specific signature mechanism?
Why did you dex? SDK 21, regardless of dex, direct fully loaded will not have any problems?

Passing the great God who seek positive solutions ...

What are the common design patterns? JS error governance programs provide you with what design patterns?
Algorithm - binary tree traversal sequence, reverse the odd-layer node traversal, even layers n preorder
What next 3 to 5 years of planning?
What do you think are your strengths? What are the disadvantages?
Now rank, how recent performance

[ 5 face - Department TL ]

Commercial sector related to Business (core commercial sector is probably the high barriers, cultivate high cost of a person, other than doing business more gold, you can accumulate a lot of business strategy knowledge), then let him ask questions
Planning the next few years? What life plan?
What do you think are your strengths? What are the disadvantages?
Now rank, how recent performance
Why such a good performance to you?
There are no other opportunities to see? Ali interview situation

[ 6 face - Big Boss ]

Algorithms - array insert, consider expansion
What encountered relatively challenging thing of the project is?
What are you responsible for the business group in the United States?
What next few years of planning?
What do you think are your strengths? What are the disadvantages?
Now rank, how recent performance

[HR] surface

Undergraduate and graduate programs are the hardware side, is there related software experience?
Is a graduate of security research or your own exam?
There are no Android development experience before going to the US Mission?
Why did you want to choose to go to the US Mission? Why did you choose to come to Beijing?
Why change jobs? The work is expected after what?

Verse: Now we grow a little technical bottlenecks encountered, plus your company has to admire a plus

Now rank, how recent performance?
Such a good performance, why not change within the US Mission department to see opportunities?
He was promoted several times, the performance highlights of what?
Where the family is that there is no intention to develop home there?
There are going to go see jobs deft like no?
Ali now ask some progress and the situation of the interview
Salary expectations

to sum up:

The interview is a continuous learning and self-improvement process, still have the opportunity to go out all things, at least to think of the effect of leak filled, and some knowledge points, you think you might know, but let's say you do not necessarily say very it is good.

Something there is pressure to have power, and learned knowledge, all the money (in most cases because technicians are rated according to your ability to paychecks), skills are more than body.

I enclose my interview finishing major topics: Interview Guide, are full of dry goods, we want to help!