Terminating a Java Program

Question

I found out ways to terminate  shut-down or stop  my Java programs   I found two solutions for it    using return When I want to quit or terminate my program execution   I add this  using System exit      Sometimes I used it  I read about Sytem exit   from This Question    So  I know a little on both them  But I am still confused as to how they actually work  Please check below codes     public class Testing    public static void main String    str        System out println 1       System exit 0       System out println 2       return         I am sure that 2 will not appear  I would like to know is why return  or other codes can write below the statement of System exit 0   and what was real definition for return   because it is strange thing for me return without any variables or values

User · Answer

System exit   is a method that causes JVM to exit  return just returns the control to calling function  return 8 will return control and value 8 to calling method

User · Answer

Because System exit   is just another method to the compiler  It doesn t read ahead and figure out that the whole program will quit at that point  the JVM quits   Your OS or shell can read the integer that is passed back in the System exit   method  It is standard for 0 to mean  program quit and everything went OK  and any other value to notify an error occurred  It is up to the developer to document these return values for any users   return on the other hand is a reserved key word that the compiler knows well  return returns a value and ends the current function s run moving back up the stack to the function that invoked it  if any   In your code above it returns void as you have not supplied anything to return

User · Answer

What does return  mean    return  really means it returns nothing void  That s it       why return  or other codes can write below the statement of System exit 0      It is allowed since compiler doesn t know calling System exit 0  will terminate the JVM  The compiler will just give a warning - unnecessary return statement

User · Answer

Calling System exit 0   or any other value for that matter  causes the Java virtual machine to exit  terminating the current process   The parameter you pass will be the return value that the java process will return to the operating system   You can make this call from anywhere in your program - and the result will always be the same - JVM terminates   As this is simply calling a static method in System class  the compiler does not know what it will do - and hence does not complain about unreachable code   return statement simply aborts execution of the current method  It literally means return the control to the calling method  If the method is declared as void  as in your example   then you do not need to specify a value  as you d need to return void   If the method is declared to return a particular type  then you must specify the value to return - and this value must be of the specified type   return would cause the program to exit only if it s inside the main method of the main class being execute   If you try to put code after it  the compiler will complain about unreachable code  for example   public static void main String    str        System out println 1       return      System out println 2       System exit 0       will not compile with most compiler - producing unreachable code error pointing to the second System out println call

User · Answer

So return  does not really terminate your java program  it only terminates your java function  void   Because in your case the function is the main function of your application  return  will also terminate the application  But the return  in your example is useless  because the function will terminate directly after this return anyway     The System exit   will completly terminate your program and it will close any open window

User · Answer

System exit   terminates the JVM   Nothing after System exit   is executed  Return is generally used for exiting a method  If the return type is void  then you could use return  But I don t think is a good practice to do it in the main method  You don t have to do anything for terminate a program  unless infinite loop or some strange other execution flows

User · Answer

Well  first System exit 0  is used to terminate the program and having statements below it is not correct  although the compiler does not throw any errors  a plain return  is used in a method of void return type to return the control of execution to its parent method

[java] Terminating a Java Program

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