call another class from java program

Question

I have 2 classes one is a simple one

Sample.java

public class Sample {
  public static void main(String args[]) {

    System.out.println("Hello World!!!!!");
  }
}

Other one is something like this

Main.java

public class Main
{  
  public static void main(String[] args) throws Exception
  {
     Runtime.getRuntime().exec("java Sample");
  }
}

I am basically trying to run the Main.java program to call Sample.java in a new command prompt...that is a new cmd that should open and print the output of Sample.java...how should I do this...???

I think it is laready answered, you can check this - [How to open the command prompt and insert commands using Java?](http://stackoverflow.com/questions/4688123/how-to-open-the-command-prompt-and-insert-commands-using-java) — Subhrajyoti Majumder, Sep 13 '13 at 07:46
Are you asking this because you want to learn about `exec` ? Or do you just dont know how to invoke methods in another class? — Gyro Gearless, Sep 13 '13 at 08:00
I know how to invoke methods from other class...the main problem is to execute the command in another cmd and then show the output there... — Rahul Mehrotra, Sep 13 '13 at 08:06

score 4 · Answer 1 · answered Sep 13 '13 at 08:02

4

Compile the two together, and then from Sample,

Main.main(args);

will do the trick. You don't need to import since you're in the same package. Note the linked tutorial. http://docs.oracle.com/javase/tutorial/java/package/index.html

answered Sep 13 '13 at 08:02

Siddh

712
4
21

1

@RahulMehrotra Can you accept this answer if it works for you? – Siddh Sep 13 '13 at 08:12
bro ..this is not what I am exactly looking for but heads up for the help.... – Rahul Mehrotra Sep 13 '13 at 08:23

score 2 · Accepted Answer · edited Sep 13 '13 at 08:03

2

Runtime.getRuntime().exec("cmd /c start cmd.exe /K \"cd <where_the_Sample_is> && javac Sample.java && java Sample\"");

or if the class is already compiled:

Runtime.getRuntime().exec("cmd /c start cmd.exe /K \"cd <where_the_Sample_is> && java Sample\"");

edited Sep 13 '13 at 08:03

jlordo

37,490
6
58
83

answered Sep 13 '13 at 08:02

stan

984
10
15

this work but the problem here is that it shows the ouput for fraction of a second and then closes..any idea as to how retain the new commandpromt..?? – Rahul Mehrotra Sep 13 '13 at 08:07
try adding " && pause" at the end of the command, for example: "cmd /c start cmd.exe /K \"cd && java Sample && pause\" – stan Sep 13 '13 at 08:11
doesnt work...it still exists – Rahul Mehrotra Sep 13 '13 at 08:16
okay I was able to make it halt by using getInt(); – Rahul Mehrotra Sep 13 '13 at 08:28

score 2 · Answer 3 · answered Sep 13 '13 at 08:06

I am using eclipse. The class files are placed in the bin directory located under the projects directory. The below code starts command prompt, changes directory to bin and issues java Sample command. You can edit it up to your requirement.

Runtime.getRuntime().exec("cmd.exe /c cd \"bin\" & start cmd.exe /k \"java Sample\"");

score 0 · Answer 4 · answered Sep 13 '13 at 08:08

0

You can use this code:

public class Main {
    public static void main(String[] args) throws Exception {
        Class<Sample> clazz = Sample.class;
        Method mainMethod = clazz.getMethod("main", String[].class);
        String[] params = null;
        mainMethod.invoke(null, (Object) params);
    }
}

answered Sep 13 '13 at 08:08

Manitra

111
5

I actually need to start a new cmd prompt and show the output there...thanks a lot for your help...:) – Rahul Mehrotra Sep 13 '13 at 08:10
Go to the directory where is Main.class is put and use java command: java Main – Manitra Sep 13 '13 at 08:14
Make sure that Main.class and Sample.class are in the same directory, otherwise you must use -classpath option of the "java" command line – Manitra Sep 13 '13 at 08:16
it is showing an error as cannot find the class Method – Rahul Mehrotra Sep 13 '13 at 08:22
Can you copy and past here the error ? – Manitra Sep 13 '13 at 08:27
error: cannot find symbol Method mainMethod = clazz.getMethod("main", String[].class); ^ symbol: class Method location: class Main1 1 error – Rahul Mehrotra Sep 13 '13 at 08:53
are you imported Method class ? "import java.lang.reflect.Method;" – Manitra Sep 13 '13 at 08:57

call another class from java program

4 Answers4