Create two threads, one display odd & other even numbers

Question

I'm trying to create two threads, one thread display even integers from 0 to 10, one thread display odd integers from 1 to 11. Is the following code suitable for designing this program?

public class Mythread {

    public static void main(String[] args) {
        Runnable r = new Runnable1();
        Thread t = new Thread(r);
        t.start();
        Runnable r2 = new Runnable2();
        Thread t2 = new Thread(r2);
        t2.start();
    }
}

class Runnable2 implements Runnable{
    public void run(){
        for(int i=0;i<11;i++){
            if(i%2 == 1)
                System.out.println(i);
        }
    }
}

class Runnable1 implements Runnable{
    public void run(){
        for(int i=0;i<11;i++){
            if(i%2 == 0)
                System.out.println(i);
        }
    }
}

Answer 1

@aymeric answer wont print the numbers in their natural order, but this code will. Explanation at the end.

public class Driver {
    static Object lock = new Object();

    public static void main(String[] args) {
        Thread t1 = new Thread(new Runnable() {
            public void run() {

                for (int itr = 1; itr < 51; itr = itr + 2) {
                    synchronized (lock) {
                        System.out.print(" " + itr);
                        try {
                            lock.notify();
                            lock.wait();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                }
            }
        });
        Thread t2 = new Thread(new Runnable() {
            public void run() {

                for (int itr = 2; itr < 51; itr = itr + 2) {
                    synchronized (lock) {
                        System.out.print(" " + itr);
                        try {
                            lock.notify();
                            if(itr==50)
                                break;
                            lock.wait();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                }
            }
        });
        try {
            t1.start();
            t2.start();
            t1.join();
            t2.join();
            System.out.println("\nPrinting over");
        } catch (Exception e) {

        }
    }
}

In order to achieve so, the run methods of the two threads above have to be called one after the other, i.e. they need to be synchronized and I am achieving that using locks.

The code works like this: t1.run prints the odd number and notifies any waiting thread that it is going to release the lock, then goes into a wait state.

At this point t2.run is invoked, it prints the next even number, notifies other threads that it is about to release the lock it holds and then goes into wait state.

This continues till the itr in t2.run() reaches 50, at this point our goal has been achieved and we need to kill these two threads.

By breaking, I avoid calling lock.wait() in t2.run and t2 thread is thus shutdown, the control will now go to t1.run since it was waiting to acquire the lock; but here itr value will be > 51 and we will come out of its run(), thus shutting down the thread.

If break is not used in t2.run(), though we will see numbers 1 to 50 on the screen but the two threads will get into a deadlock situation and continue to be in wait state.

Answer 2

I would just change a few details (no need to use the modulo operator here...):

public class Mythread {

    public static void main(String[] args) {
        Runnable r = new Runnable1();
        Thread t = new Thread(r);
        Runnable r2 = new Runnable2();
        Thread t2 = new Thread(r2);
        t.start();
        t2.start();
    }
}

class Runnable2 implements Runnable{
    public void run(){
        for(int i=0;i<11;i+=2) {
            System.out.println(i);
        }
    }
}

class Runnable1 implements Runnable{
    public void run(){
        for(int i=1;i<=11;i+=2) {
           System.out.println(i);
        }
    }
}

Answer 3

Yes it is fine. But in this case, I don't think you need 2 threads are all, because the operation is simple. However, if you are practicing threads, it is OK

Answer 4

Below is the code which uses lock on a shared object which has the number to be printed. It guarantees the sequence also unlike the above solution.

public class MultiThreadPrintNumber {
  int i = 1;

  public synchronized void printNumber(String threadNm) throws InterruptedException{

      if(threadNm.equals("t1")){
        if(i%2 == 1){
          System.out.println(Thread.currentThread().getName()+"--"+ i++);
          notify();
        } else {
          wait();
        }
      } else if(threadNm.equals("t2")){
        if(i%2 == 0){
          System.out.println(Thread.currentThread().getName()+"--"+ i++);
          notify();
        } else {
          wait();
        }
      }
      
    }

  public static void main(String[] args) {
    final MultiThreadPrintNumber obj = new MultiThreadPrintNumber();
    Thread t1 = new Thread(new Runnable() {

      @Override
      public void run() {
        try {
          while(obj.i <= 10){
            
            obj.printNumber(Thread.currentThread().getName());
          }
        } catch (InterruptedException e) {
          // TODO Auto-generated catch block
          e.printStackTrace();
        }
        System.out.println("done t1");
      }
    });
    Thread t2 = new Thread(new Runnable() {

      @Override
      public void run() {
        try {
          while(obj.i <=10){
            obj.printNumber(Thread.currentThread().getName());
          }
        } catch (InterruptedException e) {
          // TODO Auto-generated catch block
          e.printStackTrace();
        }
        System.out.println("done t2");
      }
    });

    t1.setName("t1");
    t2.setName("t2");
    t1.start();
    t2.start();
  }
}

The output will look like:

t1--1
t2--2
t1--3
t2--4
t1--5
t2--6
t1--7
t2--8
t1--9
t2--10
done t2
done t1

Answer 5

package javaapplication45;

public class JavaApplication45 extends Thread {

    public static void main(String[] args) {
        //even numbers
        Thread t1 = new Thread() {
            public void run() {
                for (int i = 1; i <= 20; i++) {
                    if (i % 2 == 0) {
                        System.out.println("even thread " + i);
                    }
                }
            }
        };
        t1.start();
        //odd numbers
        Thread t2 = new Thread() {
            public void run() {
                for (int i = 1; i <= 20; i++) {
                    if (i % 2 != 0) {
                        System.out.println("odd thread " + i);
                    }
                }
            }
        };
        t2.start();

    }

}

Answer 6

I would also look at using Java Concurrency if you want alternatives. Some of the functionality provided in the Java Concurrency package offer a higher level of abstraction then using the Thread class directly and provide more functionality as a result.

For your specific case what your doing is quite reasonable however is the order of the printing of these numbers important? Do you want evens before odds? These kinds of questions would better indicate the design that most suits your needs.

Answer 7

package thread;

import org.hibernate.annotations.Synchronize;

class PrintOdd implements Runnable {
    int count = -1;
    private Object common;

    PrintOdd(Object common) {
        this.common = common;
    }

    @Override
    public void run() {
        synchronized (common) {
            while (count < 1000) {
                try {
                    common.notifyAll();
                    System.out.println(count += 2);
                    common.wait();
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }

    }

}

class PrintEven implements Runnable {

    int count = 0;
    private Object common;

    PrintEven(Object common) {
        this.common = common;
    }

    @Override
    public void run() {
        synchronized (common) {
            while (count < 1000) {
                try {
                    common.notifyAll();
                    System.out.println(count += 2);
                    common.wait();
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }
        }

    }

}

public class PrintNatural {
    public static void main(String args[]) {
        Object obj = new Object();
        Runnable r = new PrintOdd(obj);
        Thread printOdd = new Thread(r);

        Runnable r2 = new PrintEven(obj);
        Thread printEven = new Thread(r2);

        printOdd.start();
        printEven.start();

    }

}

Answer 8

Concurrent Package:

    import java.util.concurrent.ExecutorService;

    import java.util.concurrent.Executors;
    import java.util.concurrent.Future;
    import java.util.concurrent.locks.Condition;
    import java.util.concurrent.locks.Lock;
    import java.util.concurrent.locks.ReentrantLock;
    //=========== Task1 class prints odd =====
    class TaskClass1 implements Runnable
    {

    private Condition condition;
    private Lock lock;
    boolean exit = false;
    int i;
    TaskClass1(Condition condition,Lock lock)
    {
        this.condition = condition;
        this.lock = lock;
    }
    @Override
    public void run() {
        try
        {
            lock.lock();
            for(i = 1;i<11;i++)
            {
                if(i%2 == 0)
                {
                    condition.signal();
                    condition.await();

                }
                if(i%2 != 0)
                {
                    System.out.println(Thread.currentThread().getName()+" == "+i);

                }

            }

        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally
        {
            lock.unlock();
        }

    }

}
//==== Task2 : prints even =======
class TaskClass2 implements Runnable
{

    private Condition condition;
    private Lock lock;
    boolean exit = false;
    TaskClass2(Condition condition,Lock lock)
    {
        this.condition = condition;
        this.lock = lock;
    }
    @Override
    public void run() {
        int i;
        // TODO Auto-generated method stub
        try
        {
            lock.lock();
            for(i = 2;i<11;i++)

            {

                if(i%2 != 0)
                {
                    condition.signal();
                    condition.await();
                }
                if(i%2 == 0)
                {
                    System.out.println(Thread.currentThread().getName()+" == "+i);

                }

            }

        } catch (InterruptedException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }finally
        {
            lock.unlock();

        }

    }

}
public class OddEven {

    public static void main(String[] a)
    {
        Lock lock = new ReentrantLock();
        Condition condition = lock.newCondition();
        Future future1;
        Future future2;
        ExecutorService executorService = Executors.newFixedThreadPool(2);

        future1 = executorService.submit(new TaskClass1(condition,lock));
        future2 = executorService.submit(new TaskClass2(condition,lock));
        executorService.shutdown();


    }


}

Answer 9

Not the answer for the above problem but on the similar lines.

Program to print the elements of the array sequentially but use two different threads to print the adjacent elements

import java.util.logging.Level;
import java.util.logging.Logger;

/**
 *
 * @author ntv
 */
public class PrintLAternateNumber {
    public static void main(String[] args) {
        int [] num = {1,2,3,4,5,6};
        Printer p = new Printer();
        Thread t1 = new Thread(new Thread1(num,  p), "Thread1");
        Thread t2 = new Thread(new Thread2(num,  p), "Thread2");
        t1.start();
        t2.start();
    }


}

class Thread1 implements Runnable {
    int [] num;
    Printer p ;
    public Thread1(int[] num,  Printer p) {
        this.num = num;
        this.p = p;
    }

    public void run() {
        try {
            print();
        } catch (InterruptedException ex) {
            Logger.getLogger(Thread1.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

    public void print() throws InterruptedException {
        int i = 1;

            while(i < num.length) {
                synchronized(num) {
                    while (p.evenPrinted) {
                        num.wait();
                     }
                }   

                synchronized(num) {
                     p.printEven(Thread.currentThread().getName(), num[i]);
                     i= i + 2;
                     num.notifyAll();

                }
            }
    }
}


class Thread2 implements Runnable {
    int [] num;
    Printer p ;
    public Thread2(int[] num, Printer p) {
        this.num = num;
        this.p = p;
    }

    public void run() {
        try {
            print();
        } catch (InterruptedException ex) {
            Logger.getLogger(Thread2.class.getName()).log(Level.SEVERE, null, ex);
        }
    }

    public void print() throws InterruptedException {
        int i = 0;

            while(i < num.length) {
                synchronized(num) {
                    while (!p.evenPrinted) {
                        num.wait();
                     }
                }    

                 synchronized(num) {
                     p.printOdd(Thread.currentThread().getName(), num[i]);
                     i = i + 2;
                     num.notifyAll();

                }
            }
    }
}

class Printer {
    boolean evenPrinted = true;
    void printEven(String threadName , int i) {
        System.out.println(threadName + "," + i);
        evenPrinted = true;
    }


        void printOdd(String threadName , int i) {
        System.out.println(threadName + "," + i);
        evenPrinted = false;
    }
}

Answer 10

Nos will be printed in sequence

Main class
===========
package com.thread;

import java.util.concurrent.atomic.AtomicInteger;

public class StartThread {
    static AtomicInteger no = new AtomicInteger(1);
    public static void main(String[] args) {
        Odd oddObj = new Odd();
        Thread odd = new Thread(oddObj);
        Thread even = new Thread(new Even(oddObj));
        odd.start();
        even.start();
    }
}

Odd Thread
===========
package com.thread;

public class Odd implements Runnable {

    @Override
    public void run() {
        while (StartThread.no.get() < 20) {
            synchronized (this) {
                System.out.println("Odd=>" + StartThread.no.get());
                StartThread.no.incrementAndGet();

                try {
                    this.notify();
                    if(StartThread.no.get() == 20)
                        break;
                    this.wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }

    }

}

Even Thread
===========
package com.thread;

public class Even implements Runnable {
    Odd odd;

    public Even(Odd odd) {
        this.odd = odd;
    }

    @Override
    public void run() {
        while (StartThread.no.get() < 20) {
            synchronized (odd) {
                System.out.println("Even=>" + StartThread.no.get());
                StartThread.no.incrementAndGet();
                odd.notifyAll();
                try {
                    odd.wait();
                } catch (InterruptedException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            }

        }       

    }

}

Output (Nos are printed in sequential)
======
Odd=>1
Even=>2
Odd=>3
Even=>4
Odd=>5
Even=>6
Odd=>7
Even=>8
Odd=>9
Even=>10
Odd=>11
Even=>12
Odd=>13
Even=>14
Odd=>15
Even=>16
Odd=>17
Even=>18
Odd=>19

Answer 11

public class ThreadExample {

Object lock = new Object();

class ThreadEven implements Runnable {

    @Override
    public void run() {
        int i = 2;
        while (i <= 20) {
            synchronized (lock) {
                System.out.println(i + " ");
                i = i + 2;
                lock.notify();
                try {
                    lock.wait();
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }

    }

}

class ThreadOdd implements Runnable {

    @Override
    public void run() {
        int i = 1;
        while (i <= 20) {
            synchronized (lock) {
                System.out.println(i + " ");
                i = i + 2;
                try {
                    lock.notify();
                    lock.wait();
                } catch (InterruptedException e) {

                    e.printStackTrace();
                }
            }
        }

    }

}

public static void main(String args[]) {

    ThreadExample example = new ThreadExample();
    ThreadExample.ThreadOdd odd = example.new ThreadOdd();
    ThreadExample.ThreadEven even = example.new ThreadEven();

    Thread oT = new Thread(odd);
    Thread eT = new Thread(even);

    oT.start();
    eT.start();

}

Answer 12

public class OddEvenPrinetr {
    private static Object printOdd = new Object();

    public static void main(String[] args) {

        Runnable oddPrinter =  new Runnable() {
            int count = 1;
            @Override
            public void run() {
                while(true){
                    synchronized (printOdd) {
                        if(count >= 101){
                            printOdd.notify();
                            return;
                        }
                        System.out.println(count);
                        count = count + 2;                                              
                        try {
                            printOdd.notify();
                            printOdd.wait();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                }
            }
        };


        Runnable evenPrinter =  new Runnable() {
            int count = 0;
            @Override
            public void run() {
                while(true){
                    synchronized (printOdd) {
                        printOdd.notify();
                        if(count >= 100){                       
                            return;
                        }                                       
                        count = count + 2;
                        System.out.println(count);
                        printOdd.notify();
                        try {
                            printOdd.wait();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
                }
            }
        };

        new Thread(oddPrinter).start();
        new Thread(evenPrinter).start();
    }
}

Answer 13

package p.Threads;

public class PrintEvenAndOddNum  {

    private  Object obj = new Object();

    private static final PrintEvenAndOddNum peon = new PrintEvenAndOddNum();

    private PrintEvenAndOddNum(){}

    public static PrintEvenAndOddNum getInstance(){
        return peon;
    }

    public  void printOddNum()  {
        for(int i=1;i<10;i++){
            if(i%2 != 0){
                synchronized (obj) {
                    System.out.println(i);

                    try {
                        System.out.println("oddNum going into waiting state ....");
                        obj.wait();

                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                    System.out.println("resume....");
                    obj.notify();
                }
            }
        }
    }

    public  void printEvenNum()  {
        for(int i=1;i<11;i++){
            if(i%2 == 0){
                synchronized(obj){
                    System.out.println(i);
                    obj.notify();
                    try {
                        System.out.println("evenNum going into waiting state ....");
                        obj.wait();
                        System.out.println("Notifying waiting thread ....");
                    } catch (InterruptedException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                }
            }
        }
    }   
}

Answer 14

package com.example;

public class MyClass  {
    static int mycount=0;
    static Thread t;
    static Thread t2;
    public static void main(String[] arg)
    {
        t2=new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.print(mycount++ + " even \n");
                try {
                    Thread.sleep(500);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                if(mycount>25)
                    System.exit(0);
                run();
            }
        });
        t=new Thread(new Runnable() {
            @Override
            public void run() {
                System.out.print(mycount++ + " odd \n");
                try {
                    Thread.sleep(500);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                if(mycount>26)
                    System.exit(0);
                run();
            }
        });
        t.start();
        t2.start();
    }
}

Answer 15

 public class ThreadClass {
   volatile int i = 1;
    volatile boolean state=true;

    synchronized public void printOddNumbers(){

                   try {
                       while (!state) {

                           wait();
                       }

                   } catch (InterruptedException e) {
                       e.printStackTrace();
                   }
                System.out.println(Thread.currentThread().getName()+" "+i);
                      state = false;
                      i++;
                      notifyAll();

    }

  synchronized  public void printEvenNumbers(){

      try {
          while (state) {

              wait();
          }

      } catch (InterruptedException e) {
          e.printStackTrace();
      }
      System.out.println(Thread.currentThread().getName()+" "+i);
      state = true;
      i++;
      notifyAll();

    }
}

Then call the above class like this

   // I am ttying to print 10 values.
  ThreadClass threadClass=new ThreadClass();

        Thread t1=new Thread(){
            int k=0;
            @Override
            public void run() {
                while (k<5) {
                    threadClass.printOddNumbers();
                    k++;
                }
            }
        };
        t1.setName("Thread1");
        Thread t2=new Thread(){
            int j=0;
            @Override
            public void run() {
                while (j<5) {
                    threadClass.printEvenNumbers();
                    j++;
                }
            }
        };
        t2.setName("Thread2");

        t1.start();

        t2.start();

1. Here I am trying to printing the 1 to 10 numbers.
2. One thread trying to print the even numbers and another Thread Odd numbers.
3. my logic is print the even number after odd number. For this even numbers thread should wait until notify from the odd numbers method.
4. Each thread calls particular method 5 times because I am trying to print 10 values only.

out put:

System.out: Thread1 1
System.out: Thread2 2
System.out: Thread1 3
System.out: Thread2 4
System.out: Thread1 5
System.out: Thread2 6
System.out: Thread1 7
System.out: Thread2 8
System.out: Thread1 9
System.out: Thread2 10

Answer 16

public class MyThread {

    public static void main(String[] args) {
        // TODO Auto-generated method stub

        Threado o =new Threado();
        o.start();

        Threade e=new Threade();
        e.start();    
    }    
}


class Threade extends Thread{

    public void run(){

        for(int i=2;i<10;i=i+2)
            System.out.println("evens "+i);         
    }       
}


class Threado extends Thread{

    public void run(){

        for(int i=1;i<10;i=i+2)
            System.out.println("odds "+i);          
    }       
}

OUTPUT :-

odds 1 odds 3 odds 5 odds 7 odds 9 evens 2 evens 4 evens 6 evens 8

Answer 17

public class ConsecutiveNumberPrint {

private static class NumberGenerator {

    public int MAX = 100;

    private volatile boolean evenNumberPrinted = true;

    public NumberGenerator(int max) {
        this.MAX = max;
    }

    public void printEvenNumber(int i) throws InterruptedException {
        synchronized (this) {
            if (evenNumberPrinted) {
                wait();
            }
            System.out.println("e = \t" + i);
            evenNumberPrinted = !evenNumberPrinted;
            notify();
        }
    }

    public void printOddNumber(int i) throws InterruptedException {
        synchronized (this) {
            if (!evenNumberPrinted) {
                wait();
            }
            System.out.println("o = \t" + i);
            evenNumberPrinted = !evenNumberPrinted;
            notify();
        }
    }

}

private static class EvenNumberGenerator implements Runnable {

    private NumberGenerator numberGenerator;

    public EvenNumberGenerator(NumberGenerator numberGenerator) {
        this.numberGenerator = numberGenerator;
    }

    @Override
    public void run() {
        for(int i = 2; i <= numberGenerator.MAX; i+=2)
            try {
                numberGenerator.printEvenNumber(i);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
    }
}

private static class OddNumberGenerator implements Runnable {

    private NumberGenerator numberGenerator;

    public OddNumberGenerator(NumberGenerator numberGenerator) {
        this.numberGenerator = numberGenerator;
    }

    @Override
    public void run() {
        for(int i = 1; i <= numberGenerator.MAX; i+=2) {
            try {
                numberGenerator.printOddNumber(i);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}
public static void main(String[] args) {
    NumberGenerator numberGenerator = new NumberGenerator(100);
    EvenNumberGenerator evenNumberGenerator = new EvenNumberGenerator(numberGenerator);
    OddNumberGenerator oddNumberGenerator = new OddNumberGenerator(numberGenerator);
    new Thread(oddNumberGenerator).start();
    new Thread(evenNumberGenerator).start();

}

}

Answer 18

Pretty much all that is necessary if you are asked to print even odd numbers in synchronized manner.

public class ThreadingOddEvenNumbers {

    void main(String[] args) throws InterruptedException {
        Printer printer = new Printer(57);
        Thread t1 = new Thread(new MyRunner(printer, true), "EvenPrinter");
        Thread t2 = new Thread(new MyRunner(printer, false), "OddPrinter");
        t1.start();
        t2.start();

        t1.join();
        t2.join();
    }

}

class MyRunner implements Runnable {
    private Printer p;
    private boolean evenProperty;

    public MyRunner(Printer p, boolean evenNess) {
        this.p = p;
        evenProperty = evenNess;
    }

    public void run() {
        try {
            print();
        } catch (InterruptedException ex) {
            System.out.println(this.getClass().getName() + " "
                    + ex.getMessage());
        }
    }


    public void print() throws InterruptedException {
        while (!p.isJobComplete()) {
            synchronized (p) {
                if (evenProperty)
                    while (p.isEvenPrinted()) {
                        System.out.println("wait by: "
                                + Thread.currentThread().getName());
                        p.wait();
                        if (p.isJobComplete())
                            break;
                    }
                else
                    while (!p.isEvenPrinted()) {
                        System.out.println("wait by: "
                                + Thread.currentThread().getName());
                        p.wait();
                        if (p.isJobComplete())
                            break;
                    }
            }

            synchronized (p) {
                if (evenProperty)
                    p.printEven(Thread.currentThread().getName());
                else
                    p.printOdd(Thread.currentThread().getName());
                p.notifyAll();
                System.out.println("notify called: by: "
                        + Thread.currentThread().getName());
            }
        }
    }
}

class Printer {
    private volatile boolean evenPrinted;
    private volatile boolean jobComplete;
    private int limit;
    private int counter;

    public Printer(int lim) {
        limit = lim;
        counter = 1;
        evenPrinted = true;
        jobComplete = false;
    }

    public void printEven(String threadName) {
        System.out.println(threadName + "," + counter);
        incrCounter();
        evenPrinted = true;
    }

    public void printOdd(String threadName) {
        System.out.println(threadName + "," + counter);
        incrCounter();
        evenPrinted = false;
    }

    private void incrCounter() {
        counter++;
        if (counter >= limit)
            jobComplete = true;
    }

    public int getLimit() {
        return limit;
    }

    public boolean isEvenPrinted() {
        return evenPrinted;
    }

    public boolean isJobComplete() {
        return jobComplete;
    }
}

Answer 19

public class EvenOddNumberPrintUsingTwoThreads {

    public static void main(String[] args) {
        // TODO Auto-generated method stub

        Thread t1 = new Thread() {          
            public void run() {

                for (int i = 0; i <= 10; i++) {
                    if (i % 2 == 0) {
                        System.out.println("Even : " + i);
                    }
                }

            }
        };

        Thread t2 = new Thread() {
            // int i=0;
            public void run() {

                for (int i = 0; i <= 10; i++) {
                    if (i % 2 == 1) {
                        System.out.println("Odd : " + i);
                    }
                }

            }
        };
        t1.start();
        t2.start();
    }
}

Answer 20

The Question should be: Print Odd-Even Numbers simultaneously Using Threads

public class EvenOdd1 {
        static boolean flag = true;
        public static void main(String[] args) {
            Runnable odd = () -> {
                for (int i = 1; i <= 10;) {
                    if (EvenOddPrinter.flag) {
                        System.out.println(Thread.currentThread().getName() + " " + i);
                        i += 2;
                        EvenOddPrinter.flag = !EvenOddPrinter.flag;
                    }//if
                }//for
            };

            Runnable even = () -> {
                for (int i = 2; i <= 10;) {
                    if (!EvenOddPrinter.flag) {
                        System.out.println(Thread.currentThread().getName() + " " + i);
                        i += 2;
                        EvenOddPrinter.flag = !EvenOddPrinter.flag;
                    }
                }
            };

            Thread t1 = new Thread(odd, "Odd");
            Thread t2 = new Thread(even, "Even");
            t1.start();
            t2.start();
        }
    }
/*The output => 
Odd 1
Even 2
Odd 3
Even 4
Odd 5
Even 6
Odd 7
Even 8
Odd 9
Even 10
*/

Answer 21

Simple and elegant solution -

import java.util.*;
import java.util.stream.*;  
public class OddEvenUsingTwoThreads {
   private static Object sharedObject = new Object();
   public static void main(String args[]) throws InterruptedException{
        Runnable r1 = new MyRunnable4Odd(sharedObject);
        Thread t1 = new Thread(r1);
        
        Runnable r2 = new MyRunnable4Even(sharedObject);
        Thread t2 = new Thread(r2);
        
        t1.start();
        t2.start();
        t1.join();
        t2.join();
   }   
}

class MyRunnable4Even implements Runnable{
    private Object obj;
    public MyRunnable4Even(Object sharedObj){
        this.obj = sharedObj;
    }
    @Override
    public void run() {
        for(int i=2; i<15; i+=2) {
            synchronized(obj){
              System.out.println(i);
              try{
                  obj.notify();
                  obj.wait();
              } catch(InterruptedException ie) {
                  ie.printStackTrace();
              }
            }
        }
    }
}

class MyRunnable4Odd implements Runnable{
    private Object obj;
    public MyRunnable4Odd(Object sharedObj){
        this.obj = sharedObj;
    }
    @Override
    public void run() {
        for(int i=1; i<=15; i+=2) {
            synchronized(obj){
              System.out.println(i);
              try{
                  obj.notify();
                  if(i == 15)
                    break;
                  obj.wait();
              } catch(InterruptedException ie) {
                  ie.printStackTrace();
              }
            }
        }
    }
}

Output:

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15

Explanation: It keeps printing odd and even numbers w.r.t. to two threads.

• When i=14 in MyRunnable4Even, prints '14' then this thread notifies other waiting thread and goes to waiting state.
• In MyRunnable4Odd, now i=15 gets printed, notifies even thread and shutdown the odd thread (break the loop. It doesn't go to waiting state).
• Now in MyRunnable4Even, it wakes up and checks i<15, but i=16 now. So, this thread also gets completed.