JVM's responsibility - load and run bytecode

One 、JVM Responsibility for

        JVM It exists in JRE Medium , Bytecode must depend on JVM To run , It is running all Java The virtual computer of the program .JVM It's not cross platform ,JVM Our responsibilities mainly include two parts ：

        （1） Load the specified bytecode file

        （2） Load the bytecode file into memory to run

 

Two 、JVM function class An example of 《 memoir 》

Remember the first one HelloWord Do you ？

1、 New text document , The name for HelloWord.java

2、 Enter the following code （ Use Editplus or Notepad++）

class Hello {
    public static void main(String[] args) {
        System.out.println(" elder male cousin ！ I came out ！！");
    }
}

3、 Open command window

4、 Use javac Tools , Yes HelloWord.java File compilation operation ：javac file name .java

 

5、 After compilation , Will generate HelloWord.class file （ If compilation fails , No bytecode file is generated ）

6、 start-up JVM, And load HelloWord This bytecode and execute , Grammar is ：java Class name

【 Be careful 】 The command to run is java Hello , It's not java HelloWord.class 
Run class Hello There must be main Method

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【1】JRE：Java Runtime Environment,Java Running environment

【2】JDK：Java Development Kit,Java development tool （ Including development Java All tools of the program, such as javac and java etc. ,JDK contain JRE）

【3】JVM：Java Virtual Machine,Java virtual machine