多线程一定要比单线程快吗？

1.代码展示

public class ThreadTest {
    /**
     * 问题：多线程一定要比单线程快吗?;
     */
    private static final long count = 100000;

    private static void concurrency() throws InterruptedException {
        long startTime = System.currentTimeMillis();
        Thread thread = new Thread(() -> {
            long a = 0;
            for (long i = 0; i < count; i++) {
                a += 2;
            }
        });
        thread.start();
        int b = 0;
        for (long i = 0; i < count; i++) {
            b++;
        }
        thread.join();
        long time = System.currentTimeMillis() - startTime;
        System.out.println("concurrency thread spend time: " + time);
    }

    private static void singleThread() {
        long startTime = System.currentTimeMillis();
        long a = 0;
        for (long i = 0; i < count; i++) {
            a += 2;
        }
        int b = 0;
        for (long i = 0; i < count; i++) {
            b++;
        }
        long time = System.currentTimeMillis() - startTime;
        System.out.println("single thread spend time: " + time);
    }

    public static void main(String[] args) throws InterruptedException {
        ThreadTest.concurrency();
        ThreadTest.singleThread();
    }
}