When a Java program is run, it must go through two steps: compilation and running: first, the source file with the suffix java is compiled, and finally a bytecode file with the suffix .class is generated; then the Java virtual machine will The bytecode file is interpreted and executed, and the results are displayed.
The operating environment of this tutorial: windows7 system, Dell G3 computer, java8.
#In order to facilitate the understanding of the process of running the java program, we write down the specific steps.
①Write a Hello world.java file.
②Use the "Javac Hello world.java" command to open the Java compiler and compile. After the compilation is completed, a bytecode file of Hello World. class will be automatically generated
③Use the "Java Hello world" command to start the Java virtual machine running program. The Java virtual machine will first compile the bytecode file Loading into memory, this process is called class loading, which is completed by the class loader, and then the virtual target is interpreted and executed by adding the Java class inside, and you can see the running results.
Through the above analysis, it is not difficult to find that Java programs are interpreted and executed by the virtual machine, not the operating system. [Related recommendations: "Java Video Tutorial"]
The advantage of this is that it can achieve cross-platformness, which means that the same program can be written for different operating systems and only needs to be installed Different versions of virtual machines are enough.
As can be seen from the figure, different operating systems need to use different versions of virtual machines. In this way, the Java language has the characteristics of "write once, run anywhere". It effectively solves the problem of programming languages generating different machine codes when compiled on different operating systems, greatly reducing the cost of program development and maintenance.
It should be noted that Java programs can achieve cross-platform features through the Java virtual machine, but the Java virtual machine is not cross-platform. In other words, the Java virtual machines on different operating systems are different, that is, the Java virtual machine on the Windows platform cannot be used on the Linux platform, and vice versa.
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