How to Perform Different Logic in Multiple Threads Using the Same Instance in Java

Learn how to effectively use multithreading in Java by having multiple threads perform different operations on a shared instance.
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Understanding Multithreading with Shared Instances in Java

Java's multithreading capabilities allow developers to run multiple threads concurrently, providing an efficient way to perform complex tasks. However, when dealing with shared instances, it can be tricky to ensure that different threads execute distinct logic without conflicts. This post addresses a common question: How can we have two threads perform different logic while accessing the same shared instance?

The Problem

Imagine you have two threads created from a single Runnable instance, and you want them to execute different operations: one thread should perform addition, while the other should execute subtraction using shared variables from that instance.

Example Scenario

You have the following code structure:

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If you override the run method in the Runnable class, both threads will share the same behavior, which won't solve the problem of performing distinct operations. Thus, how do you define different functionality for each thread without duplicating code?

The Solution

The key to solving this problem lies in creating separate Runnable instances for each thread, while still using the shared object for any data. Below is a simple and effective approach to implement this:

Step 1: Create Shared Variables

First, define the shared variables within a class. For example, the Main class will have two variables a and b.

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Step 2: Create Threads with Unique Logic

Create two threads, each with its own Runnable implementation that directly references the shared instance ob. Each thread will have custom logic to perform its specific task.

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Step 3: Start the Threads

Start the threads in the main method after setting up their behavior. Ensure that they run concurrently but also manage their completion using join() to maintain order if required.

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Complete Code Example

Here is the complete solution for clarity:

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Conclusion

In summary, to have two threads perform different logic on the same shared instance in Java, create separate Runnable instances for each thread that reference the shared object. This allows you to customize the actions of each thread while maintaining access to common data. By following the steps outlined above, you can effectively implement multithreading in your Java applications. Happy coding!