Introduction to Java--opening

First, the three major systems of Java

• Javase (J2SE) (JAVA2 Platform standard Edition,java platform version)
• EE (Java 2 platform,enterprise Edition,java Platform Enterprise Edition)
• Javame (J2ME) (Java 2 Platform Micro Edition,java Platform mini version)

Second, the characteristics of Java

• The Java language is simple:

  The syntax of the Java language is close to the C and C + + languages, making it easy for most programmers to learn and use. Java, on the other hand, discards features that are seldom used in C + +, which are difficult to understand and confusing, such as operator overloading, multiple inheritance, and automatic coercion of type conversions. In particular, the Java language does not use pointers, but references. and provides automatic scrap collection, which makes it unnecessary for programmers to worry about memory management.

• The Java language is object-oriented:

  The Java language provides object-oriented features such as classes, interfaces, and inheritance, and for simplicity, only single inheritance between classes is supported, but multiple inheritance between interfaces is supported, and the implementation mechanism between classes and interfaces is supported (the keyword is implements). The Java language fully supports dynamic binding, while the C + + language uses dynamic binding only for virtual functions. In short, the Java language is a purely object-oriented programming language.

• The Java language is distributed:

  The Java language supports the development of Internet applications and has a network application programming interface (Java net) in the basic Java application programming interface, which provides a class library for network application programming, including URLs, URLConnection, sockets, ServerSocket and so on. The RMI (remote method Activation) Mechanism of Java is also an important tool for developing distributed applications.

• The Java language is robust:

  Java's strong typing mechanism, exception handling, and garbage collection are important guarantees of Java program robustness. Discarding pointers is a wise choice for Java. Java's security check mechanism makes Java more robust.

• The Java language is secure:

  Java is typically used in a network environment, and Java provides a security mechanism to prevent malicious code from attacking. In addition to many of the security features of the Java language, Java has a security mechanism (class ClassLoader) for classes that are downloaded over the network, such as assigning different namespaces to prevent the substitution of locally named classes, byte code checks, and provides security management mechanisms (class SecurityManager) for Java applications to set up Security Sentinel.

• The Java language is architecture-neutral:

  Java programs (files that are suffixed with Java) are compiled into an architecture-neutral bytecode format (a file with a suffix of Class) on the Java platform and can then be run on any system that implements the Java platform. This approach is suitable for heterogeneous network environment and software distribution.

• The Java language is portable:

  This portability comes from architecture neutrality, and Java also strictly specifies the length of each basic data type. Java system itself is also very strong portability, Java compiler is implemented in Java, Java operating environment is implemented with ANSI C.

• The Java language is interpreted:

  As mentioned earlier, Java programs are compiled into bytecode format on the Java platform and can then be run on any system that implements the Java platform. At runtime, these bytecode are interpreted by the Java interpreter in the Java platform, and the classes required during execution are loaded into the runtime environment during the join phase.

• Java is high-performance:

  Java is really high-performance compared to those high-level scripting languages that are interpreted. In fact, the speed of Java is getting closer to C + + with the development of JIT (just-in-time) compiler technology.

• The Java language is multithreaded:

  In the Java language, a thread is a special object that must be created by the thread class or its child (grandchild) class. There are usually two ways to create a thread: one is to wrap an object that implements the Runnable interface into a thread using a constructor of type thread (Runnable), and another to derive a subclass from the thread class and override the Run method, and the object created with that subclass is a thread. It is important to note that the thread class has implemented the Runnable interface, so any thread has its run method, and the Run method contains the code that the thread wants to run. The activity of a thread is controlled by a set of methods. The Java language supports simultaneous execution of multiple threads and provides a synchronization mechanism between multithreading (the keyword is synchronized).

• The Java language is dynamic:

  One of the design goals of the Java language is to adapt to dynamically changing environments. The classes required by the Java program can be dynamically loaded into the runtime environment, or they can be loaded into the network to load the required classes. This also facilitates software upgrades. In addition, classes in Java have a run-time representation that enables type checking at run time.

Introduction to Java--opening