Threads are Java class that makes a program run efficiently and do multiple tasks at the same time without interrupting the main program in the background.

Threads are simply Java class that promotes efficient multi-tasking of a program at same time.

Types of Java threads

There are two types of threads in Java:

  • Extending Thread class
  • Implementing Runnable interface

Extending Thread class

If a class extends to the Thread class the thread can be run by creating an instance of class and call it’s start() method: see code⬇️

package myThreads;

public class Main extends Thread/* Here Main class extended to Thread class */{

public static void main(String[] args) {
// write your code here
Thread thread = new Thread();// here the Thread class object created
thread.start();// here the start() method is called
System.out.println("I am running outside the thread.");// this runs outside the thread

}
public void run(){
System.out.println("I am running inside the thread.");// this runs inside the thread
}
}
}

Implementing Runnable interface

If a class implements the Runnable interface, the thread can be run by passing an instance of the class to a thread object’s start() method: see code⬇️

package myThreads2;

public class Main implements Runnable{

public static void main(String[] args) {
// write your code here
Main obj = new Main();
Thread thread = new Thread(obj);
thread.start();
System.out.println("I am running outside Runnable interface");
}
public void run(){
System.out.println("I am running inside Runnable interface");

}
}

Extending threads vs. implementing Runnable interface

Extending threads:

A class extended to the thread class can’t be extended to any other class.

Implementing Runnable interface:

It is possible to extend from another class after implementing the Runnable interface. i.e. myClass extend otherClass implements Runnable {}

package myThreads2;

public class myThreads2a {
public static String aWord = "Java";
}
//this is a separate class the Main class extended from.
--------------------------------------------------------------------
//This is the main class.
package myThreads2;

public class Main extends myThreads2a implements Runnable{

public static void main(String[] args) {
// write your code here
System.out.println(aWord);
Main obj = new Main();
Thread thread = new Thread(obj);
thread.start();
System.out.println("I am running outside Runnable interface");
}
public void run(){
System.out.println("I am running inside Runnable interface");

}
}

Concurrency problems

When the threads and main program are reading and writing the same variables the values are unpredictable. This problem occurrence is called concurrency.

package myThreads;

public class Main extends Thread/* Here Main class extended to Thread class */{
static int x = 5;

public static void main(String[] args) {
// write your code here
Thread thread = new Thread();// here the Thread class object created
thread.start();// here the start() method is called
System.out.println(x);// Boss2
x++;
System.out.println(x);// Boss3

}
public void run(){
//x--;
System.out.println("Boss1"+ x--);// Boss1
}
}
// here there is conflict between these bosses

Conquering concurrency

To avoid concurrency problems it is best to share as few attributes between threads as possible. If attributes need to be shared, one possible solution is to use the isAlive() method of the thread to check whether the thread has finished running before using any attributes that the thread can change. ex.⬇️

package myThreads;

public class Main extends Thread/* Here Main class extended to Thread class */{
public static int x = 5;

public static void main(String[] args) {
// write your code here
Thread thread = new Thread();// here the Thread class object created
thread.start();// here the start() method is called
while (thread.isAlive()){
System.out.println("Loading......");
}
System.out.println(x);// Boss2
x++;
System.out.println(x);// Boss3

}
public void run(){
x++;

}
}
// here there is conflict between these bosses is solved by //displaying loading when conflict still occurs.

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