java code:

public class Hello{

    public static void main(String argv[]) {
        System.out.println("Hello ,Android java");
    }   
}

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book@book-virtual-machine:/work/java$ ls
      Hello.java
      book@book-virtual-machine:/work/java$ javac Hello.java
      book@book-virtual-machine:/work/java$ ls
      Hello.class  Hello.java
      book@book-virtual-machine:/work/java$ java Hello
      Hello ,Android java

代码编译：javac Hello.java

代码执行：java Hello