# Java Thread

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### Concurrency

<br>

* Concurrency
  * Logical
  * Single Core / Multi Core
* Parallel
  * Physical
  * Multi Core

<br>

*Since Java runs on the **JVM (Java Virtual Machine)**, you don't need to worry about the physical aspects!*

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### What is a Java Thread?

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* `Process`

  : A program that operates independently (Eclipse, Messenger, etc)
* `Thread`

  : A small unit of execution that constitutes a Process (Messenger = chat + file transfer)
* `Multi-process`

  : Running multiple processes simultaneously
* `Multi-thread`

  : Multiple threads operating simultaneously within a single process

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### Creating a Java Thread

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#### Method 1) Implementing the Runnable interface

* Runnable interface

  ex)

  ```java
  package virus;

  public class CoronaRunnable implements Runnable{

  	int num;
  	public CoronaRunnable() {}
  	public CoronaRunnable(int num) {
  		this.num = num;
  	}
  	@Override
  	public void run() {
  		for (int i =0 ; i< 10000 ; i++) {
  			int j = i*100;
  		}
  		System.out.println(num);
  	}
  }
  ```

  <br>
* Test

  ```java
  package app;

  import virus.CoronaRunnable;

  public class CoronaThreadTest {
  	public static void main(String[] args) {
  		for (int i = 0 ; i <1000 ; i++) {
  			CoronaRunnable cr = new CoronaRunnable(i);
  			Thread t = new Thread(cr);
  			// Start the Thread
  			t.start();
  		}
  	}
  }
  ```

<br>

#### Method 2) Extending the Thread class

* Thread class

  ex)

  ```java
  ```

package virus;

public class CoronaThread extends Thread{ int num;

```
public CoronaThread() {}
public CoronaThread(int num) {
	this.num = num;
}

@Override
public void run() {
	for (int i = 0 ; i < 10000 ; i++) {
		int j = i*100;
	}
	System.out.println(num);
}
```

}

````

<br>

- Test

```java
import virus.CoronaRunnable;
import virus.CoronaThread;

public class CoronaThreadTest {
	public static void main(String[] args) {
		for (int i = 0 ; i <1000 ; i++) {
			CoronaThread ct = new CoronaThread(i);
			ct.start();
		}
	}
}
````

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### Memory Structure When Running a Thread

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