Java Multithreading Essentials: Concurrency and Thread Management

Posted on Sep 20, 2025 in Computers

Java Multithreading: Concurrency Fundamentals

• Multithreading is a process to execute multiple threads simultaneously, without dependency on other threads.
• Java supports multithreaded programming, allowing you to write programs that perform many tasks concurrently.
• A multithreaded program contains two or more parts that can run at the same time. Each part of such a program is called a thread.
• The Thread class is predefined and available in the java.lang package. A thread is a basic unit of CPU execution, known for its independent operation.
• Multithreading enables the creation of highly efficient programs that maximize CPU utilization by minimizing idle time. This is particularly crucial for the interactive, networked environments where Java applications often operate, as idle time is common.

Applications Benefiting from Multithreading

Multithreading is ideal for applications with distinct tasks that can be performed independently.

• Any application with a Graphical User Interface (GUI):
  • Threads dedicated to the GUI can delegate the processing of user requests to other threads.
  • This ensures the GUI remains responsive to the user, even while complex requests are being processed in the background.
• Any application requiring asynchronous responses:
  • Network-based applications are perfectly suited for multithreading, as data can arrive from the network at any time.
  • In a single-threaded system, incoming data is queued until the single thread can read it.
  • In a multithreaded system, a dedicated thread can continuously listen for data on the network port.
  • When data arrives, this thread reads it immediately and either processes it directly or delegates its processing to another thread, ensuring timely responses.

Java Thread Support and Management

• The Java Virtual Machine (JVM) has its own runtime threads, often used for internal tasks like garbage collection.
• Threads in Java are represented by the Thread class.
• A Thread object maintains the state of the thread.
• It provides control methods such as interrupt(), start(), sleep(), yield(), and wait().
• When an application executes, the main() method is run by a single thread.
• If the application requires more threads for concurrent execution, it must explicitly create them.

How Java Threads Execute Tasks

• The Thread class contains a run() method.
• The run() method is executed when the thread’s start() method is invoked.
• A thread terminates if its run() method completes execution.
• To prevent a thread from terminating prematurely, the run() method must not end.
• Consequently, run() methods often contain an endless loop to keep the thread alive and performing its tasks.
• One thread initiates another by calling its start() method.
• The sequence of events in multithreaded programs can be confusing for those accustomed to a single-threaded model.

Multitasking in Java: Processes vs. Threads

Multitasking involves executing multiple tasks concurrently over a specified period. There are two distinct types of multitasking:

1. Process-based multitasking
2. Thread-based multitasking

Process-Based Multitasking (Multiprocessing)

Process-based multitasking, also known as multiprocessing, involves each process having its own dedicated address space in memory. This means each process allocates a separate memory area.

A process is essentially a program that is executing. Thus, process-based multitasking is the feature that allows your computer to run two or more programs concurrently. For example, it enables you to run the Java compiler at the same time you are using a text editor. In process-based multitasking, a program is the smallest unit of code that can be dispatched by the scheduler. Process-based multitasking deals with the “big picture” of concurrent program execution.

Thread-Based Multitasking (Multithreading)

Thread-based multitasking is also termed multithreading, where threads share the same address space within a single process. The thread is the smallest unit of dispatchable code.

This means that a single program can perform two or more tasks simultaneously. For instance, a text editor can format text at the same time that it is printing, as long as these two actions are being performed by two separate threads. Thus, thread-based multitasking handles the finer details of concurrent operations within a program.

Java Thread Life Cycle Stages

A thread progresses through various stages in its life cycle. For example, a thread is born, starts its tasks, runs a sequence of tasks concurrently, and then eventually terminates.

New Thread State

A new thread begins its life cycle in the New state. The thread remains in this condition until the program explicitly starts it by calling its start() method.

Runnable Thread State

As soon as the new thread starts, its status transitions to Runnable. At this stage, a thread is considered ready to execute its tasks. The thread scheduler determines when it will actually run on the CPU.

Waiting or Blocked Thread State

A Runnable thread can enter a Waiting or Blocked state for a specific interval of time. During this period, the thread is temporarily not in a Runnable condition, typically because it’s waiting for a resource, I/O operation, or another thread to complete a task (e.g., via sleep(), wait(), or I/O blocking).

Dead or Terminated Thread State

A thread enters the Dead or Terminated state when it completes its tasks, or if its run() method finishes execution. Once a thread is terminated, it cannot be restarted.