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***

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 :

Answer 1

//there are some changes in Main class and sampleCallableExample class

//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.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 : ");

}

}

//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 void call() throws Exception {

//there is change in code
//we have write all the statements, which needs to be print
globals.Update.clear();
System.out.println("Start Loop : ");
// ArrayList Update = new ArrayList();
int CurrentNum = genrand();

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

globals.Update.add(CurrentNum);

System.out.println("Number added");
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 : ");
// return globals.Update;
//we don't required any object in return

}

// As seen run wraps call object
public void run() {

try {

// Object o = call();
//just call method and make its return datatype void
call();
// System.out.println("Returned " + o);
} catch (Exception e) {

e.printStackTrace();

}

}
//there is no use of constructor that call method one time extra

// public sampleCallableExample() {
//
// try {
//
// run();
//
// } catch (Exception e) {
//
// }
//
// }
}

//globals.java

import java.util.ArrayList;

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

//output