Creating and Executing Threads

Definition

A thread is the smallest unit of execution within a Java program. Creating and executing threads allows a program to perform multiple tasks concurrently, which is known as multithreading. It enables the efficient utilization of CPU resources by allowing parts of an application to run independently in the background.

Main Content

1. The Thread Class Approach

• You can create a thread by extending the java.lang.Thread class and overriding its run() method.
• This approach is straightforward but limits the class hierarchy because Java does not support multiple inheritance; your class cannot extend any other class.

2. The Runnable Interface Approach

• You can create a thread by implementing the java.lang.Runnable interface and providing the implementation for the run() method.
• This is the preferred approach as it allows the class to extend another class, promoting better object-oriented design.

3. The Thread Lifecycle

• Threads go through various states: New, Runnable, Running, Blocked, and Terminated.
• Understanding these states is crucial for managing thread execution and avoiding common pitfalls like deadlocks.

[New] -> [Runnable] -> [Running] -> [Terminated]
             ^            |
             |----[Blocked/Waiting]----|

Visual representation of the Java Thread Lifecycle.

Working / Process

1. Defining the Task

• Create a class that implements Runnable or extends Thread.
• Place the code you want to execute concurrently inside the run() method.

2. Instantiating the Thread

• If using Runnable, create an object of your class and pass it to a new Thread constructor.
• If using Thread extension, simply instantiate your custom class object.

3. Starting the Execution

• Call the start() method on the thread object.
• The JVM invokes the run() method internally. Note: Never call run() directly, as that just executes the code in the current thread instead of starting a new one.

Advantages / Applications

• Improved Responsiveness: Multithreading prevents the UI from freezing during heavy background tasks (like file downloads or database queries).
• Resource Optimization: It allows programs to utilize multicore processors by distributing tasks across different CPU cores.
• Concurrent Task Handling: It is essential for server-side applications, such as web servers, that must handle multiple client requests simultaneously.

Summary

• Creating and executing threads in Java involves defining a unit of work via the Thread class or Runnable interface and triggering it with the start() method.
• Multithreading increases performance and responsiveness by performing parallel operations.
• Key terms to remember: Thread class, Runnable interface, run() method, start() method, and Concurrency.