is there a ‘block until condition becomes true’ function in java?

Polling like this is definitely the least preferred solution.

I assume that you have another thread that will do something to make the condition true. There are several ways to synchronize threads. The easiest one in your case would be a notification via an Object:

Main thread:

synchronized(syncObject) {
    try {
        // Calling wait() will block this thread until another thread
        // calls notify() on the object.
        syncObject.wait();
    } catch (InterruptedException e) {
        // Happens if someone interrupts your thread.
    }
}

Other thread:

// Do something
// If the condition is true, do the following:
synchronized(syncObject) {
    syncObject.notify();
}

syncObject itself can be a simple Object.

There are many other ways of inter-thread communication, but which one to use depends on what precisely you’re doing.

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