单例真的单？

单例是真正意义上的单例吗？我们下面先上单例代码

public class Sington {

    private static volatile Sington sington;
    private Sington(){}

    public static Sington getSington(){
        if(sington==null){
            synchronized (Sington.class){
                if(sington==null){
                    sington = new Sington();
                }
            }
        }
        return sington;
    }
}

测试一下

下面呢，我们就基于反射来破解单例，当然破解方式不止一种。

public static void main(String[] args) throws Exception {
    Sington sington = Sington.getSington();
    Sington sington1 = Sington.getSington();
    System.out.println(sington==sington1);

    Class aClass = Class.forName("com.mayikt.Sington");
    Constructor constructor = aClass.getDeclaredConstructor(null);
    constructor.setAccessible(true);
    Sington sington2 = (Sington)constructor.newInstance();
    System.out.println(sington==sington2);

}

所以你学会了吗？