ThreadUtils.java

import android.os.Handler;
import android.os.Looper;

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public final class ThreadUtils {

    private static volatile Handler sMainThreadHandler;
    private static volatile ExecutorService sSingleThreadExecutor;

    private ThreadUtils() {
    }

    /**
     * Returns a shared UI thread handler.
     */
    private static Handler getMainThreadHandler() {
        if (sMainThreadHandler == null) {
            sMainThreadHandler = new Handler(Looper.getMainLooper());
        }

        return sMainThreadHandler;
    }

    public static void toBackground(Runnable runnable) {
        if (sSingleThreadExecutor == null) {
            sSingleThreadExecutor = Executors.newSingleThreadExecutor();
        }
        sSingleThreadExecutor.execute(runnable);
    }

    public static void toMain(Runnable runnable) {
        getMainThreadHandler().post(runnable);
    }

}