Basic JAVA learning: command line method, environment variable configuration, basic hexadecimal conversion, sorting, and JAVA document generation (1)

1. command Line Method: doscommand line. Common command: dir: List Files in the current directory and the folder md: create directory rd: delete directory cd: Enter the specified directory cd ..: Return to the upper-level directory cd/: Return to the root directory del: delete the file exit: exit the doscommand Line help: You can view all the doscommands such as help del, you can view del usage 2. java language overview is a high-level programming language launched by SUN (Stanford University Network, Stanford University Network company) in 1995. Is an Internet-oriented programming language. As Java technology continues to mature in the web field, it has become the preferred development language for Web applications. Easy to learn, fully object-oriented, secure and reliable, and has nothing to do with the platform. 3. Features of the Java language: for cross-platform performance, you only need to install a java Virtual Machine (JVM Java Virtual Machine) on the operating system that runs Java applications. JVM is responsible for running Java programs in this system. 4. what is JRE? jdk jre (Java Runtime Environment) includes the Java Virtual Machine (JVM Java Virtual Machine) and core class libraries required by Java programs. If you want to run a developed Java program, you only need to install JRE on the computer. JDK (Java Development Kit) is provided to Java developers, including java Development tools and JRE. Therefore, if JDK is installed, you do not need to install JRE separately. Specifically, the development tool: compilation tool (javac.exe) Packaging tool (jar.exe) is used to run java programs developed with JDK. 5. Install JDK and configure the environment variables to go to www.oracle.com to download. If you are prompted to install JRE, you can skip the installation because JDK contains JRE. In the environment variable configured by the Environment Program, create the system variable JAVA_HOME = F: \ jdk1.6.0 _ 01, modify the Path system variable, and add % JAVA_HOME % \ bin at the beginning; in this way, input javac under the DOS command without reporting an error. 6. the identifier consists of 26 English letters (uppercase and lowercase) and digits: 0-9: _ $. It cannot start with a number or use the keyword JAVA Naming Convention: package name: when multiple words are made up, all letters are lowercase xxxyyyzzz variable name and function name: when multiple words are made up, the first letter of the first word is lowercase, and the second word starts with the first letter of each word. XxxYyyZzz constant name: All letters are capitalized. When multiple words are used, each word is connected by an underscore. XXX_YYY_ZZZ 7. annotations are java-specific annotations. The annotation content can be parsed by javadoc, the JDK tool, and a set of instructions for this program is generated in the form of a webpage file. 8. convert base to decimal and binary to binary: divide by 2 to take the remainder, for example, 6 binary bits 110 (1*2 (2) + 1*2 (1) + 0*2 (0) convert the binary representation to a decimal number multiplied by the power negative number of 2. The corresponding positive number binary value is reversed with 1 9. the difference between the "&" and "&" operator and the "&" OPERATOR: when a single operation is performed on the left, whether true or false, or on the right, the operation is performed on the left. If the "double" operation is performed on the right, the operation is performed on the right, if the left side is false, the right side is not involved in the operation. The difference between "|" and "|" is the same. In double or mode, the left side is true, and the right side is not involved in calculation. <Empty fill 0, removed High Discard, empty fill 0> the highest binary position of the shifted value is 0. After the right shift, the empty position is 0. The highest position is 1, fill in 1. >>> Whether the highest bit of the binary to be shifted is 0 or 1, the vacant bit is filled with 0. & Perform & operation on Binary bits. If the value is 1 & 1, the result is 1. Otherwise, the value is 0. | if the value is 0, the result is 0. Otherwise, the result is 1; ^ perform the ^ operation on any of the same binary bits. The result is 0. 1 ^ 1 = 0, 0 ^ 0 = 0 is not the same binary bits. ^ The result is 1. 1 ^ 0 = 1, 0 ^ 1 = 1 10. select the sorting method: copy the code/** select the sorting method, that is, compare the values of 5 and 3. If a small value is placed in the front, 3 is the first, and 5 is the second, then compare 3 with 1, and so on. * After comparison, it starts from the second digit, the last digit does not need to be compared */int [] array = new int [] {5, 3, 1, 6, 9}; for (int I = 0; I <array. length-1; I ++) {// array. length-1 The Last One does not need to be compared for (int j = I + 1; j <array. length; j ++) {int temp = array [I]; if (array [I]> array [j]) {array [I] = array [j]; array [j] = temp ;}}for (int I = 0; I <array. length; I ++) {System. out. println (array [I]);} copy the code Bubble sorting method: copy the code/** Bubble Sorting Algorithm to operate as follows: Compare adjacent elements. If the first is bigger than the second, exchange the two of them. * Perform the same operation on each adjacent element, starting from the first pair to the last one. At this point, the final element should be the largest number. * Repeat the preceding steps for all elements except the last one. Continue to repeat the above steps for fewer and fewer elements until there is no need to compare them. */Int [] array = new int [] {5, 3, 1, 6, 9}; for (int I = 0; I <array. length-1; I ++) {for (int j = 0; j <array. length-1-i; j ++) {int temp = array [j]; if (array [j]> array [j + 1]) {array [j] = array [j + 1]; array [j + 1] = temp ;}}for (int I = 0; I <array. length; I ++) {System. out. println (array [I]);} copy Code 11. the Inheritance in java is the keyword extends, such as class SubDemo extends Demo {} 12. the final keyword final is a modifier. classes that can be modified by class, method, and variable final cannot be inherited by final. The variable modified by final is a constant and can only be assigned a value of 13 at a time. use javadoc.exe in JDK to generate a JAVA document. Run the following command javadoc-d f: \-author-version Demo1.java. (f: \ is the location where the document is generated, and Demo1.java is the source file for the document to be generated) the generated document can only extract comments from public and protected documents. Demo1.java: copy the code package com. itcast. test; /*** create a test class * @ author yxl * @ version v1.0 */public class Demo1 {/*** add two numbers * @ param number1 * @ param number2 * @ return result of adding */public int add (int number1, int number2) {return number1 + number2 ;}}