How to install java part-4

6. Execute JAVA program:

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To execute java program, we have to use the following command or command prompt at the location where main class .class file is existed.

Java Main_Class_Name

EX: D:\java10>java FirstApp

If we provide the above command on command prompt then operating system will identify “java” command at “C:\java\jdk1.7.0_79\bin”, through path environment variable, JVM will execute “java” command, with this, JVM Software will be activated and JVM will perform the following actions:

A. JVM will take main class name from command prompt.

B. JVM will search for main class .class file at 3 locations:

i. current location,

ii. at java predefined library and

iii. at the location referred by “class path” environment variable.

C. If the required main class .class file is not identified at all the above locations then JVM will provide the following:

JAVA6: java.lang.NoClassDefFoundError: FirstApp

JAVA7: Error: Could not find or local main class: FirstApp

Note: if the required main class .class file is available at another location then to make available that .class file to JVM, we have to set “class path” environment variable.

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

D. If the required main class .class file is available at either of the above locations them JVM will load main class byte code to the memory.

E. After loading main class byte code to the memory, JVM will search for main() method at main class.

F. If the required main () method is not available then JVM will provide the following Exceptions.

JAVA6: java.lang.NoSuchMethodError: main

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

            public static void main(String[] args)

G. If the required main() method is existed in main class the JVM will execute main() method by creating a thread called as “main thread”.

H. When Main thread reached to the ending point of main() method, Main thread will come Dead State, with this, JVM will terminate all of its internal processes and JVM will go to shutdown mode.