For a period of SCJP training, I have learned a college student in school, and there are also in-service developers. Usually these students have previously been known for Java, but generally understanding the overall understanding of Java. So the students always ask, what should Java learn? What can Java do? What is applet? What is servlet, jsp, ejb? There is also WebSpere, WebLogic is doing what is doing. There is a relatively less than a relatively less known reason for the practitioners to hear too much about the Java related concepts. Learning Java language requires a process, all Java-related concepts will gradually become clear in the process of learning. The beginning of this process is to learn the standard Java technology (J2SE), then learn Java's simple web application, then distributed, and then use the mobile technology to Java, it is easy to understand. The following is some of the Java standard technologies: 1. Java's cross-platform sex, a compiled time to run simply saying that Java's cross-platform is finger, compiled Java programs can be directly different platforms This feature allows Java to spread quickly with the popularity of web applications. How is Java's cross-platform sex? This is to understand the concept of Java virtual machines and bytecodes. In fact, the compiled Java code is not a traditional binary code (such as a .exe file under Windows), but the Java bytecode, this field code file cannot be executed directly on the operating system. To run a Java program on an operating system, there must be an intermediate link to be interpreted to interpret the Java byte code into binary code. This intermediate link is a Java virtual machine (JVM). Since most operating systems have implemented JVM, Java easily implements cross-platform. Second, the surface icon object technology Java fully supports the surface icon object technology, which is reflected in the class of the Java program, which is usually composed of many Class, and these Class will have certain inheritance relationships, Java Supporting Class's single inheritance, making the inheritance relationship between classes more clear. The result of the inheritance, the polymorphism of the class, the polymorphism of the class is the implementation of the inheritance class (sub-object) of the reference access inheritance class, and this polymorphism of the class finally forms the basis of the component object model. , That is, the implementation (subclass) of the interface (parent class). Third, the I / O operation in Java is written in byte stream (Reader and Writer), and is very simple and valid using the INPUTSTREAM and OUTPUTSTREAM. The FILE class in the Java class library not only provides file operations but also contains folder operations. If you click on these lines, you can list all files under the root directory of the C drive: file f = new file ("c: //" ); String [] m_dir = f.list (); for (int i = 0; i
