Java is a widely used language, which can not only be used to develop website background, PC client and android app, but also be used in data analysis, web crawler and cloud computing.
From an academic point of view, Java is an object-oriented programming language. Beginners need to spend a lot of time to be familiar with object-oriented concepts, syntax and programming ideas. If you don’t understand something, you must adhere to it. Spending more time writing code will naturally make you suddenly enlightened.
Only by learning step by step and in a down-to-earth manner, can we go from zero foundation to entry, and then to mastery.
In the process of learning, you should also read more setsJava Tutorial, don’t gnaw at a book, so that you can learn from others and make faster progress.
What I shared today is also what I learned when I taught myself JavaGetting started with Java Tutorial, power node old Du saidGetting started with Java Basics, which is very suitable for small partners without any Java foundation or with weak foundation. It is easy to understand and very comprehensive. Since its release, it has exceeded tens of millions of playback volume and is highly praised by everyone.
The tutorial explanation pays more attention to the interaction with students, which is humorous and meticulous, covering all the core contents of javase. It goes deep into the Java virtual machine, deeply analyzes the source code, runs through the code practice, and uses project driven teaching to show the unique PDT teaching method incisively and vividly.
Java is a legend in the development of computer software in the past 10 years. Its position in the hearts of many developers can be described as “fondling”. Unlike some other computer languages, whose influence has gradually weakened over time, Java has become more powerful over time.
Since its first release, Java has jumped to the forefront of Internet programming. Each subsequent version further consolidated this position. Today, Java is still the best choice for developing web-based applications. In addition, Java is also the driving force of smartphone reform, and Android programming adopts Java language.
What is the Java language?
In short, Java is an object-oriented programming language introduced by Sun Microsystems in 1995. In 2010, Oracle acquired Sun Microsystems, and then oracle was responsible for Java maintenance and version upgrade.
In fact, Java is also a platform. The Java platform is composed of Java virtual machine (JVM) and Java application programming interface (API). Java application programming interface provides a standard interface independent of the operating system, which can be divided into basic part and extended part. After installing a Java platform on the hardware or operating system platform, Java applications can run.
The Java platform has embedded almost all operating systems. In this way, Java programs can be compiled only once and run in various systems. The Java application programming interface has developed from version 1.1x to version 1.2. The commonly used java platform is based on Java 1.6, and the latest version is java 1.8.
Since its development, Java has tried to make it omnipotent. In the world programming language rankings, Java has been ranked first in recent years, several percentage points higher than C language, which ranks second.
According to the scope of application, Java can be divided into three systems, namely Java se, Java EE and java me. These three systems are briefly introduced below.
1. Java SE
Java se (Java Platform Standard Edition), formerly known as J2SE, allows the development and deployment of Java applications used in desktop, server, embedded environment and real-time environment. Java se includes classes that support the development of Java Web services, and provides the foundation for Java EE, such as Java language foundation, JDBC operation, i/o operation, network communication, multithreading and other technologies. Figure 1 shows the architecture of Java se.
Figure 1 architecture of Java se
2. Java EE
Java EE (Java Platform Enterprise Edition) was formerly known as J2EE. Enterprise Edition helps develop and deploy portable, robust, scalable, and secure server-side java applications. Java EE is built on the basis of Java se. It provides Web services, component models, management and communication APIs, which can be used to implement enterprise level service oriented architecture (SOA) and Web 2.0 applications.
3. Java ME
Java me (Java platform Micro Edition) was formerly known as J2ME, also known as k-java. Java me provides a robust and flexible environment for applications running on mobile and embedded devices, such as mobile phones, PDAs, TV set-top boxes, and printers.
Java ME includes flexible user interface, robust security model, rich built-in network protocols and online and offline applications that can be downloaded dynamically. Applications based on the Java ME specification can be written once for many devices, and can take advantage of the native functions of each device.
Characteristics of Java language
The style of Java language is very similar to C language and c++ language. It is a pure object-oriented language. It inherits the object-oriented technical core of c++ language, but discards some shortcomings of c++, such as pointer that is easy to cause errors and multiple inheritance. At the same time, it also increases the garbage collection mechanism, releases the unused memory space, and solves the trouble of managing memory space.
Java language is a distributed object-oriented language, which has many characteristics, such as object-oriented, platform independent, simplicity, interpretation and execution, multithreading, security and so on. These characteristics are introduced one by one below.
1. Object oriented
Java is an object-oriented language, which supports classes, objects, inheritance, encapsulation, polymorphism, interfaces, packages and so on. For simplicity, Java only supports single inheritance between classes, but interfaces can be used to implement multiple inheritance. Using java language to develop programs requires using object-oriented ideas to design programs and write code.
2. Platform independence
The specific manifestation of platform independence is that Java is a language of “write once, run anywhere”, so the program written in Java language has good portability, and it is Java’s virtual machine mechanism that ensures this. After the introduction of virtual machines, the Java language runs on different platforms without recompiling.
The Java language uses the Java virtual machine mechanism to shield the relevant information of the specific platform, so that the program compiled by the Java language only needs to generate the object code on the virtual machine, and it can run on a variety of platforms without modification.
The syntax of Java language is very similar to C language and c++ language, which makes it easy for many programmers to learn. For Java, it discards many features that are difficult to understand in c++, such as operator overloading and multiple inheritance. Moreover, the Java language does not use pointers and adds a garbage collection mechanism, which solves the problem that programmers need to manage memory and makes programming easier.
4. Interpretation and Implementation
Java programs will be compiled into bytecode files when running on the Java platform, and then can be run on the operating system with Java environment. When running the file, the Java interpreter interprets and executes these bytecodes, and the classes that need to be added in the execution process are loaded into the running environment in the connection phase.
The Java language is multi-threaded, which is also a major feature of the Java language. It must be created by the thread class and its subclasses. Java supports multiple threads to execute at the same time, and provides a synchronization mechanism between multiple threads. Any thread has its own run () method, and the method to be executed is written in the body of the run () method.
Java language supports the development of Internet applications. Among the basic application programming interfaces of Java, there is a network application programming interface, which provides a class library for network application programming, including URL, urlconnection, socket, etc. The rim mechanism of Java is also an important means to develop distributed applications.
Java’s strong typing mechanism, exception handling, garbage collection mechanism and so on are all important guarantees for Java’s robustness. Discarding pointers is a major advance in Java. In addition, the exception mechanism of Java is also a great embodiment of robustness.
8. High performance
The high performance of Java is mainly relative to other high-level scripting languages. With the development of JIT (just in time), the running speed of Java is also getting higher and higher.
Java is usually used in the network environment. For this reason, Java provides a security mechanism to prevent malicious code attacks. In addition to many security features of the Java language, Java also adds a security mechanism to the classes downloaded through the network, assigns different namespaces to prevent the substitution of local classes with the same name, and includes a security management mechanism.
The numerous characteristics of Java language make it occupy a large market share in many programming languages. The object support of Java language and powerful API make the programming work easier and faster, and greatly reduce the development cost of the program. Java’s “write once, execute everywhere” is exactly one of its advantages in attracting many businesses and programmers.