Wonder Shine Blog

[OS] Thread - Java Thread

There are two ways to create thread in Java:

  1. extends Thread class, overrides run() method
  2. implements Runnable class, overrides run() method

Implementing Runnable is relatively simple:

@Data
class Sum {
    private int sum;
}

class Summation implements Runnable
{
    private int upper;
    private Sum sumValue;

    public Summation(int upper, Sum sumValue) {
        this.upper = upper;
        this.sumValue = sumValue;
    }

    public void run() {
        int sum = 0;
        for (int i = 0; i <= upper; i++) {
            sum += i;
        }
        sumValue.setSum(sum);
    }
}

After creating Thread, we have to run thread with start() method (NEVER run thread with run() method directly). start() methods works like this:

  1. Allocates Memory
  2. Initialize Thread on JVM
  3. calls run() method, let thread have opportunity to run by JVM

For example:

public class Driver {
    public static void main(String[] args) {
        Sum sumObj = new Sum();
        int upper = Integer.parseInt(args[0]);

        Thread thrd = new Thread(new Summation(upper, sumObj));
        thrd.start();
        
        try {
            thrd.join();
            System.out.println("The sum of " + upper + " is " + sumObj.getSum());
        } catch (InterruptedException ie) {
            // do nothing
        }
    }
}

Java separates thread type to

  1. Daemon
  2. Non-Daemon

Key differences is that JVM terminates after all non-daemon work terminates. On JVM start, it creates several daemon threads like garbage collector. Creating daemon thread can be done by calling:

thrd.setDaemon(true);


JAVA Thread Status

  1. new : Thread object created with new …(); call
  2. runnable : when start() command calls thread’s run() method
  3. blocked (not runnable) : io(), or sleep(), ….
  4. running : thread is on work
  5. terminated : thread done its job


Appendix: A Multithread Solution to the Producer-Consumer Problem

import java.util.Date;

public class Factory {
    public static void main(String args[]) {
        Channel<Date> queue = new MessageQueue<Date>();
    
        Thread producer = new Thread(new Producer(queue));
        Thread consumer = new Thread(new Consumer(queue));
    
        producer.start();
        consumer.start();
    }
}


References