Introduction to Java

Java language generally refers to Java (Computer programming language)

Java is an object-oriented programming language, not only absorbs the various advantages of the C + + language, but also rejects the difficult to understand C + + inheritance, pointers and other concepts, so the Java language has a powerful and easy to use two features. As the representative of static object-oriented programming language, the Java language implements the object-oriented theory, which allows programmers to do complex programming in an elegant way.

Java has the features of simplicity, object-oriented, distributed, robustness, security, platform independence and portability, multi-threading, and dynamic.  Java can write desktop applications, Web applications, distributed systems and embedded system applications, and so on? 。

Java is a generic term for the Java object-oriented programming language and Java platform introduced by Sun Microsystems Company in May 1995. Co-developed by James Gosling and co-workers, and was formally launched in 1995.

Java consists of three systems:

Javase (J2SE) (JAVA2 Platform standard Edition,java platform)?

EE (Java 2 platform,enterprise Edition,java Platform Enterprise Edition)

Javame (J2ME) (Java 2 Platform Micro Edition,java Platform mini version).?

Key Features of Java:

1. 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.

2. The Java language is object-oriented

The Java language provides primitives such as classes, interfaces, and inheritance, and for simplicity, only single inheritance between classes is supported, but 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.

3. The Java language is a seatbelt

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.

4. Java language

The statement 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.

5. 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.

6. 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).

7. 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.

The history of Java development

May 23, 1995, the Java language was born

January 1996, the first jdk-jdk1.0 was born

In April 1996, 10 of the most important operating system vendors affirmed that Java technology would be embedded in their products

In September 1996, about 83,000 Web pages applied Java technology to create

February 18, 1997, JDK1.1 released

April 2, 1997, the JavaOne meeting, the participation of more than 10,000 people, creating a record of the world's similar conference size

In September 1997, Javadeveloperconnection community members exceeded 100,000

February 1998, JDK1.1 was downloaded more than 2,000,000 times

December 8, 1998, JAVA2 Enterprise platform Java cloud release

In June 1999, Sun released three versions of Java: Standard Edition (Javase, formerly J2SE), Enterprise Edition (Java EE was formerly a Java EE), and mini-version (Javame, formerly J2ME)

May 8, 2000, JDK1.3 released

May 29, 2000, JDK1.4 released

Nokia announces June 5, 2001 that it will sell 100 million Java-enabled handsets by 2003

September 24, 2001, j2ee1.3 released

February 26, 2002, j2se1.4 released, since the Java computing power has been significantly improved

September 30, 2004 18:00pm,j2se1.5 released as another milestone in the development of the Java language. To indicate the importance of this version, j2se1.5 renamed Java SE 5.0

In June 2005, the JavaOne conference was held and Sun disclosed Java SE 6. At this point, various versions of Java have been renamed to remove the number "2": The renamed Java Ee,j2se to Java Se,j2me renamed Java ME

December 2006, Sun Company released JRE6.0

Oracle acquires Sun for $7.4 billion on April 20, 2009. Access to Java Copyright.

In November 2010, because Oracle was unfriendly to the Java community, Apache threatened to quit jcp[4].

July 28, 2011, Oracle released the official version of java7.0.

Introduction to Java