2017.10.9 Java Notes

2017.10.9 Java Notes

• No code is to see understand, is by knocking out to understand, careful! Practical! Rigorous!
• 1. What is software:
  • Common software: 1. System software: Windows, Linux, DOS; 2. Application software: QQ, Fei Qiu, etc.
• 2, Knowledge points:
  • 1.DOS common Commands
    • div: List files and files in the current directory
    • MD: Creating a directory
    • rd: Delete directory, delete directly, do not go to Recycle Bin
    • CD: Jump directory
      • CD:   Return to previous level of contents
      • CD  /return to the root directory
    • del: Delete files, cannot be used to delete folders, delete directly, do not go to Recycle Bin
    • exit: Exit the DOS command line
    • drive letter:    : Toggle Drive Letter
    • copy nul file. Suffix name: New file
  • 2. Introduction to Java
    • the Java language is an advanced computer programming language (rigorous computer programming language)
    • Java is Sun company Stanford University Nettwork by Stanford University's four programmers with 1 995 years of advanced programming language
    • Java features
      • 1, cross-platform
        • One-time compilation, multiple runs
        • principle: Whenever you need to run a Java application Install a Java (JVM) on the computer, the JVM is responsible for the Java program running in the system
        • C + +: Only run under Windows, it is Microsoft's language, Windows itself is written in the C and C + + language
      • 2, Object-oriented
        • encapsulation, inheritance, polymorphism, abstraction
      • 3, distributed
      • 4, security
        security can be divided into four levels: language and security, compile-time security, run-time security, executable code security
      • 5, Platform Independence
      • Oracle Oracle Corporation acquires Sun Company and acquires JAV Copyright of A; Java's parent: James Gosling
  • 3. Install the JDK configuration environment variable
    • JRE (Java Runtime Environment) Java Runtime is a Java program that provides the Java Core Class library and the JVM that Java programs need on different platforms including
      • 1, JVM (Java Virtual machine) Java VM
      • 2, API (application program Interface) application programming Interface
      • three key features of the JRE
        • load code: done by the ClassLoader (class loader)
        • Validate code: done by the Bytecode verifier (bytecode verifier)
        • Execute code: completed by Runtime interpreter (runtime interpreter)
      The
    • JDK (Java Develop kit) Java Development tool is provided to programmers to develop Java-used development tools with Java programs and JRE
    • if you want to run a well-developed Java application, The computer only needs to install the JRE.
    • jdk: www.oracle.com and  java.sun.com
    • installation Note: Do not have Chinese or space in the path
    • JDK directory structure:
      • Bin: Executable file for Java compiler (Javac.exe) and Java Interpreter (Java.exe)
      • Db:java developed database
      • include: Holds files for local methods
      • JRE: Runtime file for Java
      • Lib: Class library file for Java
      • SRC.ZIP:JDK provides the source code for the class
    • configuration environment variables:
      • Computer-Properties-Advanced system Settings-system settings-path: Add the Bin directory of the JDK, in the middle; semicolon split
  • 4. Execution of the first Java program
    • Requirement: Write Java program output "Hello World" in Doc-named line
    • To write the steps:
      • 1. Define a class with the class keyword to write code into the class
        • Code:
      • 2, write the main function main is called the main function, is the Java program's entrance
      • 3, SYSTEM.OUT.PRINTL output statement, output "" in the content, the statement ends with; semicolon ends
    • To run the steps:
      • 1. Write Java code into a file with a. java extension
      • 2. Compile the Java file with the Javac command
      • 3. Run the generated class file via Java command-no error can be completed
      • Create Java File--javac command compile-Generate. class bytecode file--java named run-end
    • Note: When a Java file is modified, it must be recompiled with Javac and then run with the Java command
  • 5.JAVA annotations (three types)
    • 1. Single-line comment//
    • 2. Multiline comment/* */
    • 3. Document Comment/** */
    • Statements that are commented out will no longer be executed
  • 6. Naming specification for identifier identifiers
    • (including files and folders) must begin with English words and cannot be named in Chinese
• Related information:
  • Java is a cumbersome, complex, need to understand the knowledge points, through the details of the combination
  • File not saved on desktop or C drive
  • Java is a solution to human interaction
  • Clear: (function) demand
  • Java consists of a bunch of keywords, syntax
  • Code look is ugly, you have to knock to understand
  • C is the process-oriented, Java is the face of the object
  • Big Data: Data acquisition and analytics
  • A "rigorous" computer programming language
  • Android based Java
• Professional accomplishment:
  • Expression training: Increased confidence, logical organization, ability, and adaptability
  • Quality Development: Define life goals, self-awareness and enhance comprehensive ability
  • Technical Exchange: Understand the project process, the perception of teamwork, the workplace grasp
  • Service guide: Resume, self-marketing, post-tracking
  • * Goal: What to achieve after 1-3 years, career planning, self-management, out of the comfort zone, the choice of Java EE course reasons
• Students share:
  • Bold thinking, careful to do, the details determine success or failure, standards (how to achieve, how to write, working principle), training programming interest, do not have their own time and tuition, language communication, skills, how to do the efficient, reasonable arrangement of time, how to carry out work, struggle to helpless, adhere to the move to their own!
  • Thinking change: Now it's time to study, we are a group of professional people

2017.10.9 Java Notes