Java learning basics literacy

 

Summary

 

In the past few days, I have started to learn java, and have come into contact with many concepts that are not very well understood, such as JDK, JRE, JVM, and GC. I will put them here for literacy.

 

Java

 

Java is a general term for object-oriented programming language and java platform, that is, java includes the java language and java platform.

 

Java language

Java is an object-oriented language like the C # And C ++ languages we have previously met. It has the basic features of object-oriented language, and java also has its own characteristics, for example, some features of garbage collection are added. At the same time, the programming style of java is particularly similar to that of C # And C ++. All java languages are easier to learn.

 

JDK

 

JDK is short for Java Development Kit and a software Development Kit of java. It features that every program starts from a command line call. In addition to JDK and java IDE, java IDE includes Eclipse, Myeclipse, IntelliJ, Jbuilder, Jdeveloper, Netbeans, and JCreator.

 

JRE

 

JRE is the abbreviation of Java RuntimeEnvironment. It refers to the java Runtime Environment, a set of environments necessary for java program running, including jvm and java class libraries.

 

JVM

 

The JVM, commonly known as a virtual Machine, is short for JavaVirtual Machine. A virtual Machine is a specification used for computer devices, that is, a virtual Machine is an imaginary Machine, it has its own complete hardware architecture, such as the processor, stack, register, and so on. It also has a corresponding command system, which is implemented by simulating computer hardware and software on the actual computer, so I understand it as a virtual machine as a software, just like a computer, which implements the specifications of computer devices so that java programs can run on it.

 

JVM is one of the most attractive features of java. A very important feature of Java is its independence from the platform. The use of Java virtual machines is the key to achieving this feature. General advanced languages must at least compile different target codes to run on different platforms. After the Java Virtual Machine is introduced, the Java language does not need to be re-compiled when running on different platforms. Java language usage mode: the Java Virtual Machine shields information related to specific platforms, so that the Java language compiler only needs to generate the target code (bytecode) that runs on the Java Virtual Machine ), it can be run on multiple platforms without modification.

 

GC

GC is the garbage collection mechanism, abbreviated as GarbageCollection. gc is the capability provided by jvm to release memory occupied by objects that are no longer used without any reference, note that garbage collection is the memory space occupied by objects that are not referenced, rather than those that are no longer in use.

 

 

Java platform

 

The java platform consists of Java Virtual Machine (JavaVirtual Machine) and java Application Programming Interface (ApplicationProgrammingInterface. Java application programming interface provides a standard interface independent of the operating system.

 

The java Platform consists of three systems: J2SE (Java2 Platform StandardEdition, java Platform Standard Edition), and j2EE (JavaEE (Java2 Platform, Enterprise Edition, and java Platform Enterprise Edition ), javaME (Java 2 Platform Micro Edition, java Micro Edition ).

 

All three are java platforms and are java development standards, but the scope of different standard applications is different. J2SE is the Standard Edition, J2EE is the Enterprise Edition, and j2s is the miniature edition.

 

Summary

 

Some of the above content is encountered in learning, and some are often mentioned by everyone. Through this article, I hope I can have a perceptual knowledge of this knowledge, the principle of these aspects has not been studied in depth, mainly to solve the problem of "don't know.