import java.lang.reflect.Field; 
   
import sun.misc.Unsafe; 
   
public class UnsafePlayer { 
       
    public static void main(String[] args) throws Exception {   
        //通过反射实例化Unsafe 
        Field f = Unsafe.class.getDeclaredField("theUnsafe"); 
        f.setAccessible(true);   
        Unsafe unsafe = (Unsafe) f.get(null);   
     
        //实例化Player 
        Player player = (Player) unsafe.allocateInstance(Player.class);  
        player.setName("li lei"); 
        System.out.println(player.getName()); 
           
    }   
}   
     
class Player{  
       
    private String name; 
       
    private Player(){}
       
    public String getName() { 
        return name; 
    } 
    public void setName(String name) { 
        this.name = name; 
    } 
}

/ Unsafe mechanics
private static final sun.misc.Unsafe UNSAFE;
private static final long headOffset;
static {
    try {
        UNSAFE = sun.misc.Unsafe.getUnsafe();
        Class<?> k = TransferStack.class;
        headOffset = UNSAFE.objectFieldOffset
            (k.getDeclaredField("head"));
    } catch (Exception e) {
        throw new Error(e);
    }
}
//栈顶
volatile SNode head;
//更新栈顶
boolean casHead(SNode h, SNode nh) {
    return h == head &&
        UNSAFE.compareAndSwapObject(this, headOffset, h, nh);
}

//静态属性的偏移量，用于在对应的Class对象中读写静态属性
public native long staticFieldOffset(Field f);
 
public native Object staticFieldBase(Field f);
//判断是否需要初始化一个类
public native boolean shouldBeInitialized(Class<?> c);
//确保类被初始化
public native void ensureClassInitialized(Class<?> c);
//定义一个类，可用于动态创建类
public native Class<?> defineClass(String name, byte[] b, int off, int len,
                                   ClassLoader loader,
                                   ProtectionDomain protectionDomain);
//定义一个匿名类，可用于动态创建类
public native Class<?> defineAnonymousClass(Class<?> hostClass, byte[] data, Object[] cpPatches);

//获得对象的字段偏移量   
public native long objectFieldOffset(Field f);    
//获得给定对象地址偏移量的int值
public native int getInt(Object o, long offset);
//设置给定对象地址偏移量的int值
public native void putInt(Object o, long offset, int x);

//创建对象，但并不会调用其构造方法。如果类未被初始化，将初始化类。
public native Object allocateInstance(Class<?> cls)
    throws InstantiationException;

/**
 * Report the offset of the first element in the storage allocation of a
 * given array class.  If {@link #arrayIndexScale} returns a non-zero value
 * for the same class, you may use that scale factor, together with this
 * base offset, to form new offsets to access elements of arrays of the
 * given class.
 *
 * @see #getInt(Object, long)
 * @see #putInt(Object, long, int)
 */
//返回数组中第一个元素的偏移地址
public native int arrayBaseOffset(Class<?> arrayClass);
//boolean、byte、short、char、int、long、float、double，及对象类型均有以下方法
/** The value of {@code arrayBaseOffset(boolean[].class)} */
public static final int ARRAY_BOOLEAN_BASE_OFFSET
        = theUnsafe.arrayBaseOffset(boolean[].class);
 
/**
 * Report the scale factor for addressing elements in the storage
 * allocation of a given array class.  However, arrays of "narrow" types
 * will generally not work properly with accessors like {@link
 * #getByte(Object, int)}, so the scale factor for such classes is reported
 * as zero.
 *
 * @see #arrayBaseOffset
 * @see #getInt(Object, long)
 * @see #putInt(Object, long, int)
 */
//返回数组中每一个元素占用的大小
public native int arrayIndexScale(Class<?> arrayClass);
 
//boolean、byte、short、char、int、long、float、double，及对象类型均有以下方法
/** The value of {@code arrayIndexScale(boolean[].class)} */
public static final int ARRAY_BOOLEAN_INDEX_SCALE
        = theUnsafe.arrayIndexScale(boolean[].class);

//更新变量值为x，如果当前值为expected
//o：对象 offset：偏移量 expected：期望值 x：新值
public final native boolean compareAndSwapObject(Object o, long offset,
                                                 Object expected,
                                                 Object x);
 
public final native boolean compareAndSwapInt(Object o, long offset,
                                              int expected,
                                              int x);
 
public final native boolean compareAndSwapLong(Object o, long offset,
                                               long expected,
                                               long x);

//增加
public final int getAndAddInt(Object o, long offset, int delta) {
    int v;
    do {
        v = getIntVolatile(o, offset);
    } while (!compareAndSwapInt(o, offset, v, v + delta));
    return v;
}
 
public final long getAndAddLong(Object o, long offset, long delta) {
    long v;
    do {
        v = getLongVolatile(o, offset);
    } while (!compareAndSwapLong(o, offset, v, v + delta));
    return v;
}
//设置
public final int getAndSetInt(Object o, long offset, int newValue) {
    int v;
    do {
        v = getIntVolatile(o, offset);
    } while (!compareAndSwapInt(o, offset, v, newValue));
    return v;
}
 
public final long getAndSetLong(Object o, long offset, long newValue) {
    long v;
    do {
        v = getLongVolatile(o, offset);
    } while (!compareAndSwapLong(o, offset, v, newValue));
    return v;
}
 
public final Object getAndSetObject(Object o, long offset, Object newValue) {
    Object v;
    do {
        v = getObjectVolatile(o, offset);
    } while (!compareAndSwapObject(o, offset, v, newValue));
    return v;

//取消阻塞线程
public native void unpark(Object thread);
//阻塞线程
public native void park(boolean isAbsolute, long time);
//获得对象锁
public native void monitorEnter(Object o);
//释放对象锁
public native void monitorExit(Object o);
//尝试获取对象锁，返回true或false表示是否获取成功
public native boolean tryMonitorEnter(Object o);