Execute java application

Date :july-27-2016

6.          Execute java application  :

To excite java application, we have to use the following commend prompt from the location, where main class .class file is existed.

>>javac Main_Class_Name

Ex:-

D:\java10>java FirstApp

If want above the commands on command prompt then operating system will perform the following action

1.       Operating system will tack “java” commend from commend prompt.

2.       Operating system will identify “java” commend at “C:\java\jdk1.7.0\bin” through the “path” environment variable.

3.       Operating system will activate JVM by executing “java” commends.

When JVM software is activate then JVm will perform the following actions.

a.       JVM will take main class name from command prompt which we provided along with “java” commend.

b.      JVM will search for main class .class file at current location, at java predefined library and at the location reference by the “class path” environment variable.

c.          If main class .class file is not identified at all the above locations. The JVM will provide the following messages.

JAVA6 : java.lang.NoClassDefFoundError: FirstApp

Java7: Error: Cloud not find or load main class FirstApp

Note:-

If main class .class file is available at some other location then to make available main class .class file to JVM we have to set “classpath” environment.

D:\java10>set classpath=E:\abc;

d.      If main class .class file is available at either of the above specified locations then JVM will load its byte code to the memory.

e.      After loading main class byte code to the memory JVM will search for main method. If main() method is not identified then  JVM will provide the following messages.

JAVA6:  java.lang.NoSearchMethodError: main

JAVA7: Error: main method not found in class FirstApp, please define the main method as

>>public static void main(String[] args)

f.        If main() method is identified in the loaded main class then JVM will create a thread called as “main thread” and JVM will execute main() method with main thread.

g.       Main thread execute the compile body of main()method, when main thread reach to ending point of main() method, automatically, main thread will come to dead state.

h.      When main thread is coming to dead state, JVM will stop all of its internal process which are assigned for the present program then JVM will go to shutdown mode.