| -Android System Architecture: |
1.Linux Core Layer
The Android system is based on the Linux kernel, which provides the underlying drivers for various hardware on Android devices, such as display drivers, audio drivers, camera drivers, bluetooth drivers, Wi-Fi drivers, power management, and more.
2. System Operation Bottom
-provides key feature support for Android systems through a number of C + + libraries
| Library name | function |
|---|---|
| SQLite Library | Provide support for the database |
| Opengl/es Library | Provides 3D drawing support |
| WebKit Library | Provides support for the browser kernel |
-Android Runtime Library (mainly provides some core libraries that allow developers to write Android apps using the Java language.) ）
Dalvik Virtual machines (5.0 systems changed to Art run environment) enable each Android app to run in a standalone process and have its own Dalvik virtual machine instance.
3. Application Framework Layer
The core application of the various api,android that may be used to build the application is to use these APIs, and developers can use these APIs to build their own applications.
4. Application Layer
Applications are all part of this layer, contacts, SMS, games, etc. are all.
Summarize:
| -Android App Development features: |
1. Four components
2. Rich system controls
3.SQLite Database
4. Powerful Multimedia
5. Location targeting
| -Development environment Building tools: |
1.JDK
2.Android SDK
3.Android Studio
| -Analyze Android Program: |
When you have finished creating, switch the project structure mode to project
1. Overall directory structure analysis
Description: In addition to the app directory, other directories are automatically generated. The content of the app catalog is the focus of our work.
2.APP Directory Structure Analysis
Description: The default effect of the program is not to write a line of code, directly deployed to the emulator run effect.
3. Define the main activity
<activity android:name=".MainActivity"> <intent-filter> <action android:name="android.intent.action.MAIN" /> <category android:name="android.intent.category.LAUNCHER" /> //这两句代码表示MainActivity是主活动，点击图标后首先运行此活动 </intent-filter> </activity>
Description: This code indicates the registration of the mainactivity activity, and no activity that is registered in Androidmanifest.xml is not available.
4. Main activity Analysis
package com.example.zy.myapplication;import android.support.v7.app.AppCompatActivity;import android.os.Bundle;public class MainActivity extends AppCompatActivity { protected void onCreate(Bundle savedInstanceState) { //活动被创建必须要调用下述的方法 super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); }}
Description
1. As we said before, all the things in the application that we can see are put into activities, so we must first inherit from the activity.
2. The inheritance relationship of the main activity:
3.super.oncreate (savedinstancestate) is the OnCreate constructor that invokes the parent class, which is used to create the active, Savedinstancestate is the state information that holds the current activity.
Where does 5.HelloWorld come from?
In fact, the design of the Android program is logical and view classification, it is not recommended to write the interface directly in the activity, the more common way is to write the interface in the layout file, and then introduced in the activity.
<?xml version="1.0" encoding="utf-8"?><RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:paddingBottom="@dimen/activity_vertical_margin" android:paddingLeft="@dimen/activity_horizontal_margin" android:paddingRight="@dimen/activity_horizontal_margin" android:paddingTop="@dimen/activity_vertical_margin" tools:context="com.example.zy.myapplication.MainActivity"> <TextView android:layout_width="wrap_content" android:layout_height="wrap_content" android:text="Hello World!" /></RelativeLayout>
Description: We see that there is a textview, which is an Android control that is used to display text in the layout.
6. Detailed Res directory
Description: The reason why there are so many mipmap opening folders, in fact, is mainly to allow the program to better compatible with a variety of devices.
Open the Strings.xml file under the values directory:
<resources> <string name="app_name">My Application</string></resources>
This defines a string for the application name, and we can refer to it in the following two ways:
7. Detailed Build.gradle
In the AS, we build the project through Gradle. Gradle is a very advanced project building tool that uses a groovy-based domain-specific language (DSL) to declare project settings, discarding traditional XML-based, cumbersome configurations.
I. Build.gradle at the most outer end
buildscript { repositories { jcenter() } dependencies { classpath ‘com.android.tools.build:gradle:2.1.0‘ }}allprojects { repositories { jcenter() }}
Description
Ii. Build.gradle in the app directory
apply plugin: ‘com.android.application‘android { compileSdkVersion 25 buildToolsVersion "25.0.2" defaultConfig { applicationId "com.example.zy.myapplication" minSdkVersion 15 targetSdkVersion 25 versionCode 1 versionName "1.0" } buildTypes { //用于指定生成安装文件的相关配置，一般有release和deubug两项。 release { minifyEnabled false //是否对代码进行混淆 proguardFiles getDefaultProguardFile(‘proguard-android.txt‘), ‘proguard-rules.pro‘ //代码的混淆规则 } }}dependencies { //用于指定当前项目的所有依赖关系 compile fileTree(dir: ‘libs‘, include: [‘*.jar‘]) //上着为本地依赖关系,将libs目录下*jar包添加到构建路径当中 testCompile ‘junit:junit:4.12‘ //声明测试用例库的 compile ‘com.android.support:appcompat-v7:25.2.0‘ //这是一个标准的远程依赖库格式,Gradle在构建项目时会检查是否有此库的缓存,如果没有则联网下载.添加依赖库声明:compile project(‘:helper‘),将helper依赖关系加入.}
Description
| -Visibility: |
1. Private members of the parent class also inherit from the quilt class, although these private members cannot be accessed directly by member names, but can be accessed indirectly.
| -Inter-Class inheritance relationship design: |
1: What is the permission modifier, what role does he have, and why he needs him;
A Java application has many classes, but some classes do not want to be used by other classes. There are data members and method members in each class, but not every data and method is allowed to be called in other classes. How can access control be achieved? You will need to use the access-rights modifier.
| 1. The permission modifier is used to control the visible range of the modified variable, method, class. That is, its scope of action; |
There are 4 types of permission modifiers in 2:java:
| 1 public type; 2.public can be decorated with classes, member variables, constructor methods, method members. 3. Members that are modified by public can be called in any class, regardless of the same package or different packages, 4. Is one of the most privileged modifiers |
| 1. Private type; 2. You can modify member variables, construct methods, member methods, and not decorate classes (this refers to external classes, regardless of inner classes). 3. Private-decorated members can only be used in the class in which they are defined and cannot be called in other classes. |
| 1. Default type defaults; 2. Can be used to modify the class, member variables, construction methods, methods, all can use the default permissions, that is, no keywords are written. 3. The default permissions are the same as package permissions, and the elements of the same package permission are called only in the class in which they are defined, and in the same package class. |
| 1. Protection type Protect; 2. You can modify data members, construct methods, method members, and cannot decorate classes (this refers to external classes, regardless of inner classes). 3. Members that are modified by protected can be called in the class that defines them, in the same class as the package. 4. If classes with different packages want to invoke them, then the class must be a subclass of the class that defines them. |
Image:
3: There are several issues to be aware about permission modifiers;
| 1. Not every modifier can be decorated with a class (meaning an external class), only public and default can. 2. All modifiers can be decorated with data members, method members, and construction methods. 3. For the sake of code security, the modifier should not use as much permission as possible, but applicable. For example, data members, if there is no special need, use private as much as possible. Enhance the encapsulation of the; 4. Modifiers are decorated with "accessed" permissions. |
| This This is an object of its own, representing the object itself, which can be understood as: A pointer to the object itself. The usage of this can be broadly divided into 3 types in Java:
|
| Super Super can be understood as a pointer to a super (parent) class object, which refers to a parent class closest to itself. There are three ways to use super:
|
| The similarities and differences between Super and this: Super (parameter): Call one of the constructors in the base class (should be the first statement in the constructor) This (parameter): Calls another form of the constructor in this class (should be the first statement in the constructor) Super: It refers to a member in the immediate parent class of the current object (used to access member data or functions in the parent class that is hidden in the immediate parent class, when the base class has the same member definition as in the derived class, such as super. Variable name super. member function by name (argument) This: it represents the current object name (where it is easy to generate two semantics in the program, you should use this to indicate the current object, if the function's shape participates in the class member data has the same name, this should be used to indicate the member variable name) The call to super () must be written on the first line of the subclass construction method, otherwise the compilation does not pass. The first statement of each subclass construction method is implicitly called super (), and if the parent does not have this form of constructor, it will be error-free at compile time. Super () is similar to this (), except that super () calls the constructor of the parent class from the subclass, and this () invokes other methods within the same class. Super () and this () all need to be placed in the first row within the construction method. Although you can call a constructor with this, you cannot call two. This and super can not appear in a constructor at the same time, because this is bound to call other constructors, the other constructors will inevitably have a super statement exists, so in the same constructor has the same statement, it loses the meaning of the statement, the compiler will not pass. This () and super () all refer to objects, so they cannot be used in a static environment. Includes: static variable, static method, static statement block. Essentially, this is a pointer to this object, but super is a Java keyword. |
In February 1995, James Gosling published a Java white paper titled "Java Overview," which explains why Java does not support multiple inheritance.
| Java removes some features that are rarely used in C + + and are often misunderstood, such as the overloads of the operator (operator overloading) (although Java still retains the overloads of the method), multiple inheritance (multiple inheritance), and extensive automatic forcing of the same type (extensive automatic coercions). |
| Java: A simple, object-oriented, distributed, interpretive (translator Note: Java is neither a purely explanatory nor a purely compiled language), robust, secure, architecture-neutral, portable, high-performance, multi-threaded, dynamic language. |
This is why we have removed multiple inheritance in order to enhance the simplicity of this feature. Here's an example of a multi-inheritance diamond inheritance problem.
Tupian
There are two classes B and C that inherit from a. Suppose B and C both inherit the method of a and overwrite it, and write their own implementation. Assuming D inherits B and C through multiple inheritance, D should inherit the overloaded methods of B and C, so which one should it inherit? Is it B's or C's?
C + + often falls into this trap, although it also presents an alternative approach to solving the problem. We don't have this problem in Java. Even if two interfaces have the same method, the implemented class will have only one method, which is written by the implemented class. Dynamic load classes make it difficult to implement multiple inheritance.
First question: In Java, arrays is
A. Primitive data types
B. Objects
C. Interfaces
D. Primitive data types if the type stored in the array was a primitive data type and objects if the type stored in the ARR Ay is an object
E. Strings
Analysis: The index value must be greater than or equal to 0 and less than the number of elements of the array. If there are X elements in the array, the index value is 0~x-1.
Analysis: A parameter is defined as a variable that is initially declared as a type parameter name. Here, the type is int[] and the parameter is a.
Analysis: First bank account; reserve memory space for Firstentity Bank, which itself is a reference variable pointing to bankaccount[] objects. First Bank account = new bank account [1000]; instantiate bankaccount[] object is 1000 BankAccount object.
Analysis: The first declaration declarations A and B are all arrays of int. The second declaration declares that C and D are ints, but for D, an int array. Both a B and d are arrays of int.
Analysis: This makes two arrays the same, so the arrays referenced by A and B are the same, so one is called another alias.
Analysis: After the Java command, anything entered at the command line will be accepted as a command-line argument. If a few words are separated by a space, then each word is stored as a separate string array element.
Parsing: An array index must be of type int, or it can be extended to a value of type int (therefore, char, Byte, and short are also allowed).
Analysis: One drawback of an array is its fixed size. Once instantiated, its size is fixed. ArrayList is a class that uses an array, which automatically creates a larger array and copies the old array into the new array, so that the ArrayList can be larger as needed. While this resolves the problem of throwing exceptions, it does result in poor performance because each time you increase the ArrayList size, you must copy from one array to another.
Analysis: Java provides a special notation for variable-length parameter lists. Ellipsis (...) Used to specify a variable-length parameter list.
Analysis: When inserting or deleting the first part of a ArrayList, a large number of element copies occur, reducing its efficiency.
Based on the scoring criteria, I scored this blog: xx points. The score is as follows: XXX
Reference example
A lot of concepts, hooves look closely, there are many details, and the previous chapters are closely related.
Learning progress Bar| lines of code (new/cumulative) | Blog Volume (Add/accumulate) | Learning Time (new/cumulative) | Important Growth | |
|---|---|---|---|---|
| Goal | 5000 rows | 30 Articles | 400 hours | |
| First week | 95/95 | 1/1 | 18/18 | |
| Second week | 515/620 | 1/2 | 22/40 | |
| Third week | 290/910 | 1/3 | 20/60 | |
| Week Four | 1741/2651 | 1/4 | 30/84 | |
| Week Five | 579/3230 | 1/5 | 20/104 | |
| Week Six | 599/3829 | 1/6 | 18/122 | |
| Seventh Week | 732/4561 | 1/6 | 24/146 |
Reference: Why is it so difficult to estimate software engineering applications, software engineering estimation methods
Planned study time: 22 hours
Actual learning time: 24 hours
Improvement: slightly.
(See more modern software engineering courseware
Software engineer Competency Self-evaluation table)
"First line of code Android"
Why Java does not support multiple inheritance
20172327 2017-2018-2 first line of Android first chapter study summary
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