如下Unsafe源码所示，Unsafe类为一单例实现，提供静态方法getUnsafe获取Unsafe实例，当且仅当调用getUnsafe方法的类为引导类加载器所加载时才合法，否则抛出SecurityException异常。

public final class Unsafe {
  // 单例对象
  private static final Unsafe theUnsafe;

  private Unsafe() {
  }
  @CallerSensitive
  public static Unsafe getUnsafe() {
    Class var0 = Reflection...