How can I pass a parameter to a Java Thread?

java

thread-safety

parameter-passing

java-threads

byAlex Kataev·Sep 12, 2024

Quick solution: pass a parameter to a Java Thread by creating a custom class implementing the Runnable interface. This class should have a constructor accepting your specific parameter, for usage within the run() method.

Example:

public class Task implements Runnable {
    private String taskMessage; // Our "task-specific" message

    public Task(String taskMessage) {
        this.taskMessage= taskMessage;
    }

    @Override
    public void run() {
        // Have the thread speak the message
        System.out.println("Message: " + taskMessage);
    }
}

// Usage:
Thread t = new Thread(new Task("Hello, Thread!"));
t.start();  // Voila! Thread goes live with a "Hello"

Going the extra mile with parameters in threads

Dynamic parameter changes

Threads are not just about start-and-go, they might need to change gears on the go. Here's how to implement setter methods to allow for dynamic parameter changes. Remember, thread safety is key, ensure methods are synchronized or use atomic references.

Ensuring parameter visibility

Sharing parameters? Use volatile for visibility! The volatile keyword ensures thread-to-thread visibility for variables, helping keep memory errors at bay.

public class SharedTask implements Runnable {
    // Our thread-safe shared message
    private volatile String sharedMessage;

    public void setSharedMessage(String message) {
        this.sharedMessage = message;
    }

    @Override
    public void run() {
        while(!Thread.currentThread().isInterrupted()) {
            if(sharedMessage != null) {
                // Check if the shared message has something and print it
                System.out.println("Shared Message: " + sharedMessage);
            }
        }
    }
}