[Problem] Three Thread Synchronization Using State Pattern

Problem

Create three threads

  • one that print '1' for 5 times.

  • one that print '2' for 5 times.

  • one that print '3' for 5 times.

Need to implement coordination between them so that  1, 2 and 3 should be printed in order from the three threads:

1

2

3

1

2

3

...

Hint: The order should be same theoretically and practically. Putting a sleep while printing might work in some cases, but it cannot be guaranteed always.

 

Solution

We will use an enum to implement the state pattern and use it for coordination.

package com.javajee.threads;

public class ThreeThreadSynchronization {

  public static State currentState = State.ONE;
  public static Object lockObject = new Object();

  public static void main(String[] args) {
    Thread t1 = new Thread(new MyRunnable(State.ONE));
    Thread t2 = new Thread(new MyRunnable(State.TWO));
    Thread t3 = new Thread(new MyRunnable(State.THREE));
    t1.start();
    t2.start();
    t3.start();

  }

}

class MyRunnable implements Runnable {

  State allowedState;

  public MyRunnable(State allowedState) {
    this.allowedState = allowedState;
  }

  @Override
  public void run() {
    for (int i = 0; i < 10; i++) {
      synchronized (ThreeThreadSynchronization.lockObject) {

        while (allowedState != ThreeThreadSynchronization.currentState) {
          try {
            ThreeThreadSynchronization.lockObject.wait();
          } catch (InterruptedException e) {
            e.printStackTrace();
          }
        }

        System.out.println(allowedState.getVal());
        ThreeThreadSynchronization.currentState = ThreeThreadSynchronization.currentState.nextState();
        ThreeThreadSynchronization.lockObject.notifyAll();
      }
    }

  }

}

enum State {
  ONE(1) {
    @Override
    public State nextState() {
      return TWO;
    }

  },
  TWO(2) {
    @Override
    public State nextState() {
      return THREE;
    }
  },
  THREE(3) {
    @Override
    public State nextState() {
      return ONE;
    }
  };

  private int val;

  State(int val) {
    this.val = val;
  }

  public abstract State nextState();

  public int getVal() {
    return val;
  }
}
 

Search the Web

Custom Search

Searches whole web. Use the search in the right sidebar to search only within javajee.com!!!

Quick Notes Finder Tags

Activities (1) advanced java (1) agile (3) App Servers (6) archived notes (2) ArrayLists (1) Arrays (2) Best Practices (12) Best Practices (Design) (3) Best Practices (Java) (7) Best Practices (Java EE) (1) BigData (3) Chars & Encodings (6) coding problems (2) Collections (15) contests (3) Core Java (All) (52) course plan (2) Database (12) Design patterns (8) dev tools (3) downloads (2) eclipse (9) Essentials (1) examples (14) Exception (1) Exceptions (4) Exercise (1) exercises (6) Getting Started (18) Groovy (2) hadoop (4) hibernate (77) hibernate interview questions (6) History (1) Hot book (4) http monitoring (2) Inheritance (4) intellij (1) java 8 notes (4) Java 9 (1) Java Concepts (7) Java Core (7) java ee exercises (1) java ee interview questions (2) Java Elements (16) Java Environment (1) Java Features (4) java interview points (4) java interview questions (4) javajee initiatives (1) javajee thoughts (3) Java Performance (6) Java Programmer 1 (11) Java Programmer 2 (8) Javascript Frameworks (1) Java SE Professional (1) JSP (1) Legacy Java (1) linked list (3) maven (1) Multithreading (16) NFR (1) No SQL (1) Object Oriented (9) OCPJP (4) OCPWCD (1) OOAD (3) Operators (4) Overloading (2) Overriding (2) Overviews (1) policies (1) programming (1) Quizzes (17) references (2) resources (1) restful web service (3) Searching (1) security (10) Servlets (8) Servlets and JSP (31) Site Usage Guidelines (1) Sorting (1) source code management (1) spring (4) spring boot (1) Spring Examples (1) Spring Features (1) spring jpa (1) Stack (1) Streams & IO (3) Strings (11) SW Developer Tools (2) testing (1) troubleshooting (1) user interface (1) vxml (8) web services (1) Web Technologies (1) Web Technology Books (1) youtube (1)