Java Threads
Threads help to perform multiple things at the same time. For example, listening to the radio while eating.
Create a Java thread
There are two ways to create a Java thread: extends the Thread class or implements the Runnable interface.
Extend the Thread class
Extend the Thread class and override its run() method. Code example:
MyThread1 class:
package com.devspeedup.java.thread.thread;
public class MyThread1 extends Thread {
public void run() {
for (int i = 1; i < 100; i++) {
System.out.println("Thread 1: eating - " + i);
}
}
}MyThread2 class:
package com.devspeedup.java.thread.thread;
public class MyThread1 extends Thread {
public void run() {
for (int i = 1; i < 100; i++) {
System.out.println("Thread 1: eating - " + i);
}
}
}TestThread class:
package com.devspeedup.java.thread.thread;
public class TestThread {
public static void main(String[] args) {
Thread t1 = new MyThread1();
t1.start();
Thread t2 = new MyThread2();
t2.start();
}
}Test result:
Implement the Runnable interface
Implement the Runnable interface and implement its run() method. Code example:
MyThread1 class:
package com.devspeedup.java.thread.runnable;
public class MyThread1 implements Runnable {
public void run() {
for (int i = 1; i < 100; i++) {
System.out.println("Thread 1: eating - " + i);
}
}
}MyThread2 class:
package com.devspeedup.java.thread.runnable;
public class MyThread2 implements Runnable {
public void run() {
for (int i = 1; i < 100; i++) {
System.out.println("Thread 2: listening to the radio - " + i);
}
}
}TestThread class:
package com.devspeedup.java.thread.runnable;
public class TestThread {
public static void main(String[] args) {
Runnable obj1 = new MyThread1();
Runnable obj2 = new MyThread2();
Thread t1 = new Thread(obj1);
Thread t2 = new Thread(obj2);
t1.start();
t2.start();
}
}Test result:
Calling start() vs run()
Calling the start() method creates a new thread while calling the run() method doesn’t. If you mean to create a new thread but calling the run() method, it is a mistake.
Try both examples above again but this time instead of calling the start() method, try to call the run() method directly and check the results.
TestThread2 classes:
package com.devspeedup.java.thread.thread;
public class TestThread2 {
public static void main(String[] args) {
Thread t1 = new MyThread1();
Thread t2 = new MyThread2();
// Mistakenly calling the run() method
t1.run();
t2.run();
}
}package com.devspeedup.java.thread.runnable;
public class TestThread2 {
public static void main(String[] args) {
Runnable obj1 = new MyThread1();
Runnable obj2 = new MyThread2();
Thread t1 = new Thread(obj1);
Thread t2 = new Thread(obj2);
// Mistakenly calling the run() method
t1.run();
t2.run();
}
}Calling the run() method resulted in the run() method of t1 finishes first then the run() method in t2 starts. This is not what we want to achieve: multithreading (having multiple threads running concurrently).
