Introduction to Java
Java was developed by Sun Microsystems company in 1995 to launch a Java object-oriented programming language and the Java platform in general. Jointly developed by James Gosling and colleagues, and officially launched in 1995.
Java is divided into three systems:
- JavaSE (J2SE) (Java2 Platform Standard Edition, java Platform, Standard Edition)
- JavaEE (J2EE) (Java 2 Platform, Enterprise Edition, java platform enterprise edition)
- JavaME (J2ME) (Java 2 Platform Micro Edition, java Platform, Micro Edition).
In June 2005, JavaOne Conference, SUN company publicly Java SE 6. At this point, Java's various versions have been renamed to cancel the numbers which "2": J2EE renamed Java EE, J2SE renamed Java SE, J2ME renamed Java ME.
Key Features
- Java language is simple:
Java language syntax of C and C ++ language is very close, so that most programmers are easy to learn and use. On the other hand, Java discarded rarely used in C ++, it is difficult to understand, confusing those features, such as operator overloading, multiple inheritance, automatic type coercion. In particular, Java language does not use the pointer, but the reference. And provides automatic garbage collection, so that the programmer does not have to worry about memory management.
- Java language is object-oriented:
Java language provides classes, interfaces, and object-oriented features such as inheritance, for simplicity, only supports single inheritance between classes, but support multiple inheritance between interfaces, and supports the implementation mechanism between the classes and interfaces (keyword implements). Full support for dynamic binding Java language, C ++ language and only use dynamic binding of virtual functions. In short, Java language is a pure object-oriented programming language.
- Java language is distributed:
Java language to support the development of Internet applications, there is a network application programming interface (java net) in the basic Java application programming interface, which provides a programming library for network applications, including URL, URLConnection, Socket, ServerSocket and so on. The Java RMI (remote method activation) mechanism is also an important means of distributed application development.
- Java is a robust language:
Java's strong typing, exception handling, automatic garbage collection, etc. is important to ensure the robustness of Java programs. Discard pointer is a smart choice for Java. Java's security checks make Java more robust.
- Java is a safe language:
Java is often used in a network environment, for which, Java provides a safety mechanism to prevent malicious code. In addition to the Java language has many security features, Java has a security mechanism (class ClassLoader) on the network to download classes, such as different namespaces to prevent the distribution of alternative local class of the same name, byte code inspection, and provide security management mechanism (class SecurityManager) allows Java applications to set the security guards.
- Java is a language-neutral architecture:
Java program (suffix java files) on the Java platform-neutral architecture is compiled into bytecode format (suffix class files), then the system can run on any Java platform to achieve this. This approach is suitable for distributed network environments and heterogeneous software.
- Java language is portable:
This portability from system configuration neutrality, addition, Java also strict requirements of the respective basic data type length. Java system itself is very portable, Java compiler is implemented in Java, Java runtime environment is implemented in ANSI C.
- Java language is interpreted:
As described above, the Java platform Java program is compiled into byte code format, then the system may be implemented in any Java platform to run. At runtime, a Java platform Java interpreter to interpret the byte code execution, during the execution of the class need to be loaded into the runtime environment in the coupling stage.
- Java is a high-performance:
Compared with those high-level scripting language interpreted, Java is indeed a high-performance. In fact, Java's speed with the development of JIT (Just-In-Time) compiler technology closer and closer to C ++.
- Java is a multithreaded language:
In the Java language, the thread is a special object, it must be created by the Thread class or sub (Sun) class. There are generally two ways to create threads: First, using the type of structure Thread (Runnable) The configuration of a sub-class object that implements Runnable interface packaged into a thread, the other derived from the Thread class and subclass override run method, the object of the subclass is the creation of a thread. It is noteworthy that the Thread class already implements the Runnable interface, so any one thread has its run method, and run method contains the code thread to run. Thread activity is controlled by a set of methods. Java language support multiple threads execute simultaneously, and provides a synchronization mechanism (keyword synchronized) between multiple threads.
- Java language is dynamic:
One of the design goals of Java language is adapted to the dynamic environment. Java program requires classes can be dynamically loaded into the execution environment, may need to load classes over a network. It is also helpful to upgrade the software. Further, Java classes representing a run time, and can run time type checking.
Development History
- May 23, 1995, Java language was born
- In January 1996, the first birth of a JDK-JDK1.0
- In April 1996, 10 major operating system vendors declare JAVA technology will be embedded in their products
- In September 1996, about 83,000 Web pages utilize JAVA technology to produce
- 1997 February 18, JDK1.1 release
- 1997 April 2, JavaOne conference, more than a thousand participants, a then record the scale of its kind worldwide conference
- In September 1997, JavaDeveloperConnection community members over one hundred thousand
- In February 1998, JDK1.1 been downloaded more than 2,000,000 times
- 1998 December 8, JAVA2 J2EE enterprise platform release
- In June 1999, SUN Java has released three versions: Standard Edition (JavaSE, formerly J2SE), Enterprise Edition (JavaEE formerly J2EE) and Micro Edition (JavaME, formerly J2ME)
- 2000 May 8, JDK1.3 release
- 2000 May 29, JDK1.4 release
- 2001 June 5, NOKIA announced that by 2003, will sell 100 million mobile phones that support Java
- 2001 September 24, J2EE1.3 release
- 2002 February 26, J2SE1.4 release, since Java computing power has increased dramatically
- On September 30, 2004 Ri 18:00 PM,J2SE1.5 release, another milestone in the history of the Java language development. In order to express the importance of this version, J2SE1.5 renamed Java SE 5.0
- In June 2005, JavaOne Conference, SUN company publicly Java SE 6. At this point, Java's various versions have been renamed to cancel one of the numbers "2": J2EE renamed Java EE, J2SE renamed Java SE, J2ME renamed Java ME
- In December 2006, SUN has released JRE6.0
- April 20, 2009, Oracle's $ 7.4 billion acquisition of Sun. Java is copyrighted.
- November 2010, due to Oracle Java community unfriendly, so Apache threatened to withdraw from JCP [4].
- July 28, 2011, Oracle released the official version of Java7.0.
- March 18, 2014, Oracle company issued a Java SE 8.
- September 21, 2017, Oracle released Java SE 9 companies
- March 21, 2018, Oracle released Java SE 10 companies
- September 25, 2018, Java SE 11 release
- March 20, 2019, Java SE 12 release
Java development tools
Java language try to ensure that the system memory over 1G, other tools are as follows:
- Linux system, Mac OS systems, Windows 95/98/2000 / XP, WIN 7/8 system.
- The JDK 7, 8 ...... the Java 12 , 13 relatively new
- Notepad editor or other editor.
- The IDE: the Eclipse , best to use IDEA
After installing the above tools, we can output Java first program "Hello World!"