自己实现一个AtomicInteger

import sun.misc.Unsafe;
import java.io.Serializable;
import java.lang.reflect.Field;

public class MyAtomicInteger implements Serializable {
    private static final long serialVersionUID = 6214790243416807051L;

    private volatile Integer num;

    public MyAtomicInteger(Integer num) {
        this.num = num;
    }

    private Unsafe unsafe;
    private Long numOffset;

    {
        try {
            Field field = Unsafe.class.getDeclaredField("theUnsafe");
            field.setAccessible(true);
            unsafe = (Unsafe) field.get(null);
            numOffset = unsafe.objectFieldOffset(MyAtomicInteger.class.getDeclaredField("num"));
        } catch (NoSuchFieldException | IllegalAccessException e) {
            e.printStackTrace();
        }
    }

    public int getAndSet(int num) {
        return unsafe.getAndSetInt(this, numOffset, num);
    }

    public final boolean compareAndSet(int expect, int update) {
        return unsafe.compareAndSwapInt(this, numOffset, expect, update);
    }

    public final int getAndIncrement() {
        return unsafe.getAndAddInt(this, numOffset, 1);
    }

    public final int getAndDecrement() {
        return unsafe.getAndAddInt(this, numOffset, -1);
    }

    public Integer get() {
        return num;
    }

    public void set(Integer num) {
        this.num = num;
    }
}