CODEWITHSUNDEEP
javaconsole
adeel iqbal
adeel iqbal

Reputation: 494

run a java file within another java file and display its output to console

i have a hello world class hworld.class which displays "Hello World" on the console. i am trying to run it from another class in console using the code 

 public class ftest2  
 {  
    public static void main(String[] arg)  
    {  
     System.out.println("NEW FILE PRINT LINE EXECUTED");
      try {  
            Process pro1 = Runtime.getRuntime().exec("javac hworld.java");  
            pro1.waitFor();  
            Process pro2 = Runtime.getRuntime().exec("java hworld");  
            pro2.waitFor();  
         } catch (Exception e) {    
               System.out.println("Some Error");   
               e.printStackTrace();     
                }  
    }  }

but when the file is executed, the output of Hello World is not displayed on the console.
the program just starts and displays 

  NEW FILE PRINT LINE EXECUTED

insted of 

  NEW FILE PRINT LINE EXECUTED    
  HELLO WORLD

how it would be possible to display the output of HELLO WORLD as well.
(it is example program. i want to display the output of a program within another program)

if there is another way to call a class within another class to display its output. then please mention it.

Upvotes: 1

Views: 5116

Answers (3)

assylias
assylias

Reputation: 328737

You need to redirect the inputstream of your process to System.out, for example:

public static void main(String[] arg) {
    System.out.println("NEW FILE PRINT LINE EXECUTED");
    try {
        Process pro1 = Runtime.getRuntime().exec("javac hworld.java");
        try (BufferedReader reader = new BufferedReader(new InputStreamReader(pro1.getInputStream(), Charset.forName("UTF-8")))) {
            String line;
            while ((line = reader.readLine()) != null) {
                System.out.println(line);
            }
        }
    } catch (Exception e) {
        e.printStackTrace();
    }
}

Note: it uses the try with resources syntax of Java 7 but is easily transposable to Java 6- if necessary.

Upvotes: 1

burna
burna

Reputation: 2962

You need to read in the InputStream of the process, which is

The stream obtains data piped from the standard output stream of the process represented by this Process object.

Source: http://docs.oracle.com/javase/1.4.2/docs/api/java/lang/Process.html#getInputStream()

Read InputStream and write out to System.out:

    InputStream inputStream = process.getInputStream();
    int b = -1;
    while ( (b =  inputStream.read()) != -1 ) {
        System.out.write(b);
    }

Upvotes: 5

vels4j
vels4j

Reputation: 11298

Might be you are getting exception and you've not printed it.

public class ftest2  
 {  
    public static void main(String[] arg)  
    {  
     System.out.println("NEW FILE PRINT LINE EXECUTED");
      try {  
            Process pro1 = Runtime.getRuntime().exec("javac hworld.java");  
            pro1.waitFor();  
            Process pro2 = Runtime.getRuntime().exec("java hworld");  
            pro2.waitFor();  
         } catch (Exception e) {
            System.out.println("Some Error");
            e.printStackTrace(); 
         }  
    }  
}

and another way

public static void main(String[] arg)  
{  
     System.out.println("NEW FILE PRINT LINE EXECUTED");
     hworld.main(arg); // since main is a static method can be called w/o instance
}

Upvotes: 0

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