Question

my goal is to generate a random number every 10 seconds and store in arraylist. when I generate the new number every 10 second I want to update the previous number from the arraylist. currently it gets the first current number in main method but when I store after 10 second i'm not getting the update current number. I would appreciate any help. NOTE: ***I want the Runnable to be in the same class, Not in main method. my goal is to send the arraylist that has the update number*** ***PLEASE I want to get the current number from main method loop*******

import java.util.ArrayList;

import java.util.Random;

import java.util.concurrent.Executors;

import java.util.concurrent.ScheduledExecutorService;

import java.util.concurrent.TimeUnit;

import java.util.concurrent.Callable;

import java.util.concurrent.FutureTask;

public class Main {

public static void main(String[] args) throws Exception {

ScheduledExecutorService executor = Executors.newScheduledThreadPool(1);

// schedule thread for evry 10 seconds

System.out.println("Start Loop : ");

executor.scheduleAtFixedRate(new sampleCallableExample(), 0, 10, TimeUnit.SECONDS);

System.out.println("array size:" + globals.Update.size());

for (int x = 0; x < globals.Update.size(); x++) {

System.out.println("Current Num = " + globals.Update.get(x));

}

System.out.println("Close Loop : ");

}

}

package com.Test;

import java.util.concurrent.Callable;

import java.util.concurrent.FutureTask;

import java.util.Random;

class sampleCallableExample implements Runnable {

public static int genrand() {

Random number = new Random();

// generate random number

int rand = number.nextInt(1000);

// return generated random number

return rand;

}

public Object call() throws Exception {

// ArrayList Update = new ArrayList();

int CurrentNum = genrand();

System.out.println("generate number ==== " + CurrentNum);

globals.Update.clear();

globals.Update.add(CurrentNum);

System.out.println("Number added");

return globals.Update;

}

// As seen run wraps call object

public void run() {

try {

Object o = call();

// System.out.println("Returned " + o);

} catch (Exception e) {

e.printStackTrace();

}

}

public sampleCallableExample() {

try {

run();

} catch (Exception e) {

}

}

}

package com.Test;

import java.util.ArrayList;

public class globals {

public static ArrayList Update = new ArrayList();

}

The Current output is:

Start Loop :

generate number ==== 992

Number added

array size:1

Current Num = 992

Close Loop :

generate number ==== 407

Number added

generate number ==== 32

Number added

However, It should be:

Start Loop :

generate number ==== 992

Number added

array size:1

Current Num = 992

Close Loop :

Start Loop :

generate number ==== 407

Number added

array size:1

Current Num = 407

Close Loop :

Start Loop :

generate number ==== 32

Number added

array size:1

Current Num = 32

Close Loop :

NOTE: ***I want the Runnable to be in the same class, Not in main method. my goal is to send the arraylist that has the update number*** ***PLEASE I want to get the current number from main method loop******

Answer 1

Hi,

I understand your concern. but please understand that if you keep the code in main method, there is no chance that the code in main method will be executed. becuase the code we are writing will be executed for every 10 seconds is teh Runnable class, not main method.

So to get the desired output, the possibility is to put the code related to main method in run method of runnable class so that for every 10 seconds run method being called by schedular so that we will get the desired output.

Please find the below code.

====================================================

sampleCallableExample.java

====================================================

package runnable;

import java.util.Random;

public class sampleCallableExample implements Runnable {

   public static void main(String[] args) {

   }

   public static int genrand() {
       Random number = new Random();
//generate random number
       int rand = number.nextInt(1000);
//return generated random number
       return rand;
   }

   public Object call() throws Exception {
//ArrayList Update = new ArrayList();
       int CurrentNum = genrand();
       System.out.println("generate number ==== " + CurrentNum);
       globals.Update.clear();
       globals.Update.add(CurrentNum);
       System.out.println("Number added");
       return globals.Update;
   }

// As seen run wraps call object
   public void run() {
       try {
           System.out.println("Start Loop : ");
           Object o = call();
//System.out.println("Returned " + o);
           System.out.println("array size:" + globals.Update.size());

           for (int x = 0; x < globals.Update.size(); x++) {

               System.out.println("Current Num = " + globals.Update.get(x));

           }

           System.out.println("Close Loop : ");
       } catch (Exception e) {
           e.printStackTrace();
       }
   }

   public sampleCallableExample() {
       try {

           run();

       } catch (Exception e) {
       }

   }

}
=============================================

Main.java

=============================================

import java.util.ArrayList;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.TimeUnit;

public class Main {
   public static void main(String[] args) throws Exception {

       ScheduledExecutorService executor = Executors.newScheduledThreadPool(1);

//schedule thread for evry 10 seconds
//executor.schedule(new sampleCallableExample(), 1, TimeUnit.MILLISECONDS);
       executor.scheduleAtFixedRate(new sampleCallableExample(), 0, 10, TimeUnit.SECONDS);
   }
}

class globals {
   public static ArrayList Update = new ArrayList();

}

Sample output:

Start Loop: generate number ==== 876 Number added array size: 1 Current Num = 876 Close Loop: Start Loop: generate number ==== 714 Number added array size: 1 Current Num = 714 Close Loop: Start Loop: generate number ==== 855 Number added array size:1 Current Num = 855 Close Loop: Start Loop: generate number ==== 479 Number added array size: 1 Current Num = 479 Close Loop:

I hope this helps you!!

Thanks.