What is Difference between Callable and Runnable interface?

In Java, both the Callable and Runnable interfaces play essential roles in multithreaded programming. They provide a way to execute code concurrently and achieve parallelism.

While both interfaces serve similar purposes, there are notable differences between them.

This article aims to explore and explain the distinctions between the Callable Interface in Java and the Runnable interface in Java.

But before that, let's explore what the Callable and Runnable interfaces in Java are.

Overview of Callable Interface in Java

The Callable interface in Java is a fundamental part of the java.util.concurrent package. It was introduced in Java 5 as part of the java.util.concurrent framework, it provides a way to represent a task that can be executed asynchronously and can return a result.

The Callable interface in Java is defined as follows:

public interface Callable<V> {

V call() throws Exception;

}

The Callable interface in Java is a parameterized interface, where V represents the type of result that the task will produce. The key method in the Callable interface is the call() method, which is responsible for executing the task and returning a result of type V. The call() method may also throw an exception of type Exception.

When a task needs to be executed, it can be submitted to an ExecutorService, a thread pool responsible for managing the execution of tasks.

The ExecutorService assigns the task to a worker thread, invoking the call() method on the Callable object. The result produced by the call() method can be obtained through a Future object, representing the result of an asynchronous computation.

One of the primary advantages of the Callable interface in Java is its ability to return a result. This makes it suitable for scenarios where the task's outcome needs to be captured and utilized further.

For example, when performing complex calculations, making network requests, or retrieving data from a database, the Callable interface lets you retrieve the computed result once the task is completed.

Additionally, the Callable interface supports throwing checked exceptions from the call() method. This enables proper exception handling within the task and provides more flexibility in dealing with potential errors or exceptional conditions during the task execution.

By declaring that the call() method throws an exception, developers can handle specific exceptions and take appropriate actions based on the task's outcome.

The Callable interface in Java is widely used in concurrent programming scenarios where parallel execution and efficient resource utilization are crucial.

By leveraging the Callable interface, developers can achieve greater concurrency, optimize performance, and improve responsiveness in applications that require executing multiple tasks concurrently.

Overall, the Callable interface in Java is vital in multithreading and concurrent programming capabilities. Its integration with the Executor framework provides a powerful mechanism for executing tasks asynchronously, obtaining results, and handling exceptions effectively, contributing to developing high-performance and scalable applications.

Overview of Runnable Interface in Java

The Runnable interface in Java is a fundamental part of the language's multithreading capabilities. It belongs to the java.lang package and is used to represent a task or a unit of work that can be executed concurrently.

The Runnable interface is defined as follows:

public interface Runnable {

void run();

}

The Runnable interface in Java contains a single method called run(), which represents the entry point for the task execution. When a class implements the Runnable interface, it must provide an implementation for the run() method.

The logic and operations that need to be executed concurrently are typically written within this method.

To execute a task represented by a Runnable object, it must be passed to a thread for execution. The thread's start method invokes the run() method of the Runnable object, executing the task in a separate thread.

Unlike the Callable interface, the Runnable interface in Java does not return a result. It is primarily used for tasks that do not produce a result or when the result is not needed.

Instead, the focus of the Runnable interface is on performing actions or operations concurrently without the need for returning a value.

The simplicity of the Runnable interface in Java makes it easy to implement and understand. It provides a straightforward way to define and execute tasks concurrently.

This simplicity also allows the Runnable interface to be used in various scenarios, such as updating shared resources, performing periodic operations, or triggering events.

The Runnable interface in Java is commonly used in conjunction with the Thread class or the Executor framework for managing threads and executing tasks concurrently.

When using the Thread class, a Runnable object is passed as a parameter to the Thread's constructor, and the thread is started using the start method.

Alternatively, when using the Executor framework, a Runnable object can be submitted to an ExecutorService, which manages the execution of tasks in a thread pool.

Now that we are aware of the definitions of the Callable and Runnable Interfaces let's move on to the comparison between the two.

Comparison between Callable and Runnable Interfaces

Here are some of the comparisons between the Callable and Runnable Interfaces in Java:

Return Value: The most significant difference between the Callable Interface in Java and the Runnable interface in Java is that Callable allows returning a result after execution, while Runnable does not. Callable achieves this by defining the call() method with a return type, whereas Runnable has the void return type for its run() method.

Exception Handling: Callable allows the call() method to throw checked exceptions, which must be handled or declared in the method signature. In contrast, Runnable does not allow checked exceptions to be thrown from its run() method.

Use Cases: Callable is commonly used in scenarios where the result of a task is required, such as performing calculations or retrieving data from a remote source. Runnable, on the other hand, is suitable for scenarios where a result is not needed, such as updating a shared resource or triggering an event.

Executor Service: Both Callable and Runnable interfaces are used with the Executor framework in Java for thread management and executing tasks concurrently. The Executor framework provides methods to submit Callable and Runnable tasks for execution.

Conclusion

In summary, the Callable interface in Java and the Runnable interface in Java provide ways to execute code concurrently and achieve parallelism.

The Callable interface in Java is designed for tasks that require returning a result and supports throwing checked exceptions.

In contrast, the Runnable interface in Java is used for tasks that do not produce a result and do not throw checked exceptions.

Understanding the differences between Callable and Runnable interfaces is crucial for effective multithreaded programming in Java, enabling developers to choose the appropriate interface based on their specific requirements.