Question

I'm generating a random number every 10 second and Storing and Updating the number every 10 second when I generate new number in UpdateInt method. However, In my main method when I called UpdateInt method it generate every 10 second new number but it doesn't update and store in the arraylist.

***I want the Runnable to be in the arraylist method. Not in main method. my goal is to send the arraylist that has the update number***

import java.util.ArrayList;

import java.util.Random;

import java.util.concurrent.Executors;

import java.util.concurrent.ScheduledExecutorService;

import java.util.concurrent.TimeUnit;

public class EverySecond {

public static int genrand() {

Random number = new Random();

//generate random number

int rand = number.nextInt(1000);

//return generated random number

return rand;

}

public static ArrayList<Integer> UpdateInt(){

ArrayList<Integer> Update = new ArrayList<Integer>();

Runnable helloRunnable = new Runnable() {

public void run() {

int CurrentNum = genrand(); //create a random number

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

Update.add(CurrentNum);//update it in array list

}

};

ScheduledExecutorService executor = Executors.newScheduledThreadPool(1);

//schedule thread for evry 10 seconds

executor.scheduleAtFixedRate(helloRunnable, 0, 10, TimeUnit.SECONDS);

return Update;

}

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

ArrayList<Integer> getUpdate=UpdateInt();

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

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

}

}

}

Current Output:

generate number ==== 367

generate number ==== 944

It should be :

generate number ==== 367

Current Num = 367

generate number ==== 47

Current Num = 47

NOTE: ***I want the Runnable to be in the arraylist method. Not in main method. my goal is to send the arraylist that has the update number***

I should get the same number in main method when Ioop that I generated in UpdateInt method. Note: I want the Runnable() to be in arraylist method and return the arraylist that has the update number. I would apperciate any help.

Answer 1

Hi,

Please find updated code below.

For this since we return a value we need a callable wrapped around in runnable.

runnable is required to run at every 10 seconds.

Callable is required to return updated array.

As demonstrated in program below.

Main.java :

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
  
//executor.schedule(new sampleCallableExample(), 1, TimeUnit.MILLISECONDS);
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));
  
}
  
}
}

Kindly declare Update array as global variable: inside new class globals as shown below:

import java.util.ArrayList;
public class globals
{
public static ArrayList<Integer> Update = new ArrayList<Integer>();
  
}

sampleCallableExample.java :

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<Integer> Update = new ArrayList<Integer>();
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)
{
}
  
}
  
}   

output attached: You can see current num and generated number updated.

Thanks,

kindly upvote.