Dark Horse programmer-Java overview, dark horse java Overview

Dark Horse programmer-Java overview, dark horse java Overview

I,JavaLanguage overview and three major technical architectures

1,JavaLanguage Overview

Java is an Internet-Oriented Programming Language launched by SUN in 1995. It has the following features: Object-oriented, universal, efficient, secure, and cross-platform. As Java technology continues to mature in the web field, it has become the preferred development language for Web applications.

2,JavaThree major technical architectures

Java consists of four aspects: Java programming language, Java file format, Java Virtual Machine (JVM), Java application interface (Java API)

Java has three technical architectures:

(1) J2EE (Java 2 Platform Enterprise Edition): known as JAVAEE after JDK, it is a set of solutions for developing applications in an Enterprise environment. Technologies included in this technology system, such as Servlet Jsp, are mainly used for Web application development.

(2) J2SE (Java 2 Platform Standard Edition): After jdk5.0, it is called JAVASE. It is the main learning content in the basic stage of java and contains classes that constitute the core of Java. For example, database connection, interface definition, input/output, and network programming.

(3) Java 2 Platform Micro Edition: later than jdk5.0, it is called JAVAME. This technology is mostly used in embedded development of some electronic products.

II,JavaVirtual Machine,JavaRunning environment,JavaOperating Mechanism

1,JavaVirtual Machine (full name:JavaVirtual Machine. Abbreviation:JVM)

Java Virtual Machine (VM) is an abstract computer that simulates various computer functions on an actual computer. The Java Virtual Machine has its own complete hardware architecture, such as the processor, stack, and register, as well as corresponding command systems. JVM shields information related to the specific operating system platform, so that Java programs can run on multiple platforms without modifying the bytecode generated on the Java Virtual Machine. This also makes Java powerful cross-platform capabilities.

Java virtual machines are not cross-platform. different operating systems have different JVM versions. Common JVM versions include Windows, Linux, and MAC.

2,JavaBuild running environment

(1) JRE (Java Runtime Environment): Java Runtime Environment, including "Java Virtual Machine" and "core class libraries required by Java programs ". If you only need to run the developed Java program, you only need to install JRE on the computer.

(2) JDK (Java Development Kit): Java Development Kit (SET), mainly including JRE and Java Development tools. Java development tools include: compilation tool (javac.exe) Packaging tool (jar.exe) and so on.

3,JavaOperating Mechanism

III,JavaEnvironment variable configuration steps

1Download firstJDKAnd install.

2, ConfigurationJavaTo configure environment variables, follow these steps:

• Right-click "my computer"> "environment variable ";
• Create a JAVA_HOME variable in the system variable. The variable value is C: \ Program Files \ Java \ jdk1.6.0 _ 14 (based on your JDK installation path );
• Create a classpath variable with the variable value:.; % JAVA_HOME % \ lib \ tools. jar;
• Add the variable value % JAVA_HOME % \ bin; % JAVA_HOME % \ jre \ bin in the path variable (no need to create a new variable) (note that the variable values are separated );

3To test whether the environment variable configuration is successful:

Click "start"-> "run" on the computer, type "cmd", and type A command line window. In the command line window, enter commands such as java-version, java, and javac to check whether java-related prompts are displayed. If so, the environment variables are successfully configured.

IV,JavaNote

Java has three formats of Annotations: single-line, multi-line, and document annotations.

1.Single line comment:

Format: // comment content. // all content that ends after the beginning of the line will be ignored by the compiler.

2.Multi-line comment

Format: All characters in/* Comment content */,/*/are ignored by the compiler.

3.Document comment

Format:/** comment content */. All characters between/***/are ignored by the compiler and java-specific (used to generate documents ). It is usually written before classes, domains, constructors, methods, and definitions. The description content can be parsed by javadoc.exe, a tool in JDK, and a set of description documents for this program, which are reflected in Webpage files.

Note:Annotations usually have two functions: (1) annotation of the program code; (2) it can be used to debug the program.

V,JavaIdentifier naming rules in

(1) It consists of letters, numbers, underscores, and $. It cannot start with a number.

(2) Java is a strong language that is case sensitive.

(3) keywords and reserved words in java cannot be used.

(4) do not use the class name in the Java API as your class name.

6. the habit of writing code for beginners

The process of implementing human thinking in programming. Therefore, beginners can sort out their own programming ideas and then use programming languages to implement them. You can sort out your programming ideas in the form of annotations. The format is as follows:

/*

Requirement: Description of function implementation;

Ideas: 1 ,...... 2 ,......

Step: 1 ,...... 2 ,......

*/

The example of getting started is as follows:

/*

Requirements:Practice a hello world Program.

Ideas:

1. Define a class. Because java programs define classes, java programs exist in the form of classes. The form of classes is actually the final embodiment of a bytecode file.

2. Define a main function. To enable this class to run independently.

3. Because the hello world demo is displayed on the console, you need to use the output statement.

Steps:

1. Use the class keyword to define the class and start a class name with high readability.

2. main Function: public static void main (String [] args) in a fixed format. Jvm knowledge.

3. Use the output statement: System. out. println ("hello world ").

*/

Class Demo {

// Define a main function to ensure independent operation of the program.

Public static void main (String [] args ){

// This is the output statement used to print the data in parentheses to the console. ln can wrap at the end of the data.

System. out. println ("hello world ");

}

}

 

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