Thread Subclass Must Override run()

ID

java.thread_subclass_must_override_run

Severity

info

Remediation Complexity

trivial

Remediation Risk

low

Remediation Effort

low

Resource

Reliability

Language

Java

Tags

concurrency, reliability

Description

Reports classes that extend Thread without overriding the run() method. A Thread subclass that does not override run() executes the empty default implementation, making the thread effectively a no-op.

Rationale

When a class extends Thread, the intent is to define the thread’s behavior by overriding run(). If run() is not overridden, calling start() creates a new OS thread that immediately terminates without doing any work. This is almost always a bug or an oversight. Abstract classes are excluded because they may intentionally delegate run() to a concrete subclass.

// Bad -- the thread does nothing
class WorkerThread extends Thread {
    private final String name;

    WorkerThread(String name) {
        this.name = name;
    }
    // Missing run() override!
}

Remediation

Override run() to define the thread’s behavior, or use Runnable instead of subclassing Thread:

// Option 1: override run()
class WorkerThread extends Thread {
    @Override
    public void run() {
        doWork();
    }
}

// Option 2: prefer Runnable (more flexible)
Thread t = new Thread(() -> doWork());
t.start();

References