Java Basic Learning Note day011. Software development: Software: A collection of computer data and instructions organized in a specific order: Software development: Developing software with development tools and computer Language 2.java Overview: The father of Java: James Goslin Jdk:java Development environment Jre:java operating environment Jvm:java Virtual Machine Java cross-platform because the JVM can run on different platforms, JVM is cross-platform Javase: Standard Edition Javame: Mobile, IoT Java EE: Enterprise Edition, Internet Project 3.java language Features: Simple interpretative object-oriented high performance Distributed multi-threaded robust dynamic structure independent security open source cross platform 4. What is cross-platform: an application written in Java that can run 5.HelloWorld program parsing on different system platforms through different versions of the JVM: first write the Java source Code program, the extension. ja VA in the command line mode, enter the Javac command to compile the source file, generate the bytecode file J Avac Helloworld.java compile completed, if no error, input Java, the class bytecode file interpretation run execution do not need to add. class Extension: Java HelloWorld6. Common error: 1. File extension hidden causes compilation error 2.class write wrong, Class clsss ... 3. Class name format problem, temporarily use all English 4. The curly braces that match the class name are incorrect for the 5.main method format is incorrect 6.main method curly brace missing 7. Print statement spelling error 8. The quotation marks are used incorrectly and the Chinese full-width quotation mark 7 is used. FAQ: A: Extension is hidden how to find: --Folder Options--View--Remove the check mark of the hidden extension B: I want the file name to be the same as the class name. In fact, it is possible not to do so. Note, however, that javac followed by the filename + extension Java followed by the class name without the extension C:java language is strictly case-sensitive, please note. There is also the word don't write wrong. D: See illegal characters: \65307 must be a Chinese question. We write procedures that require punctuation marks to be all in English state. E: The pairing problem of parentheses. In general, the parentheses are paired up. F: Encountered in the class HelloWorld cannot find the main method, please define the main method is definitely the main method of the format problem. 8.DOS command: Windows+r open run, enter CMD carriage return CD. Return to the top level directory cd\ return to the root directory dirDisplay the current directory contents CD into the specified directory D: Go to the D-disk directory CLS clears the screen contents 9. Comments://single-line comment/* Multiline comment *//** Document Comment *//Note is a programmer must have good programming habits,//Beginner program can be developed: write the comments before Write code//explain the program, improve the readability of the program, can help us to debug 10.helloworld program: public class Helloworld{public static void Main (string[] args) { System.out.println ("HelloWorld");}} Public: Permission modifier: Common, Maximum Permissions class: Classes HelloWorld: Class name, to be consistent with file name static: Static modifier Main: Method Name, Main method, word given special meaning, entry of program string[] args: Accept array of String type, args: Parameter name System.out.println: Output statement and wrap 11. Keywords: words that are assigned special meanings by the system, have special meanings, compose letters all lowercase 12. Identity (Zhi four tones): A~z,a~z,0~9, Underline _, Dollar sign $ number can not start, can not repeat with the keyword, it is best to see the name of the 13. Constant in the course of program execution, the value cannot be changed constant classification: literal value constant custom constant integer constant: all integers: 10,20,30 decimal constant: All decimals: 1.2,3.1,4.10 word Constant: The contents enclosed in single quotation marks: ' A ', ' B ', ' C ' Boolean constants: More specific, only true and false Null constants: null Java has four forms for constants: binary: Consists of 0 and 1, starting with 0b decimal: 0~9, integer default is decimal octal: Composed of 0~7, starting with 0 hex: by 0~9,a~f, starting with 0 x 14. Basic type: Integer (byte,short,int,long), float (float,double) character type (char): null character ' is not supported in Java ', special characters need to be added ' \ ' Boolean (Boolean): True,false Reference type: Class, Interface (interface), array ([]) public class HelloWorld//class {public static void Ma In (string[] args)//main method, entry of the program{System.out.println ("HelloWorld");//Output Print HelloWorld}}
Java Basic Learning Note day01
