Java Fundamentals 01

1.

/** * JDK:  (Java  Development ToolKit)  Java Development Kit. The JDK is the core of the entire Java! *        includes the Java Runtime Environment JRE (Java Runtime envirnment), a stack of Java tools and a Java        -based class library (Java Api===>java application interface, In fact, Daniel wrote us some of the class files)! *    *   J2SE: Standard Edition (edition)   *    *   java EE: Enterprise Edition (Enterprises  Edition) *    *   J2ME: Mobile device (Micro Edition) * * * *    Jre:java operating Environment (Java Runtime Envirnment), is the Java platform we often say! All Java programs must be in the JRE environment to run! *     contains the core class library of Jvm,java! But does not include the development tool----compiler, debugger! *    JVM: (Java  virtial  mechinal) Java virtual Machine  , part of the JRE! *    Main work: Interpret your own bytecode files, and map to local CPU instructions to inherit OS system calls! *    Java is a cross-platform, is based on the JVM! Use the JVM's mapping rules to make it irrelevant to the operating system! *    */

the difference between the three JDK,JRE,JVM

2.

/*   * Use Notepad to develop the first Java applet * * 01. You must have configured the environment variable win+r after you enter cmd Click OK input java enter input Javac return * does not appear The error message indicates that the configuration was successful! * 02. In a suitable place (below the Java folder under the e:/java/e disk) * Create a Helloword.java file = = = "java source file = = =" All files ending in. java * 03. Writing Java Generation                                               Code * * Public class helloword{*//single-line comment does not compile when running * public static void Main (string[] args) {//java program entry, main thread * System. Out.print ("Good afternoon, everyone!")                                     ");                                                                   *       }                                                                *    } * 04. We can read it!  Want to make the computer understand, need to compile this. java file * 001.win+r input cmd Enter * 002. Locate the directory where the file is located pushd (e:/java) file, enter * 003. Input Javac The file name. Java carriage return will find a. class file in the file's directory * file name is not case-sensitive * compile this. java file into a. class file so that the computer can read the bytecode file = = = "All in. c  Lass End of File *. class file We can't read it!You can use the Anti-compilation tool to decompile the. class file into a. java file * 05. Execute the. class file to get the results we want * Java file name here do not need to write. class * File names are case-sensitive   */

Notepad development of the first Java program

Java Fundamentals 01