用java的反射机制,能不能调用到单例模式类中的方法(非静态)?

Question

1.HelloWorld 类:
public class HelloWorld {
private static HelloWorld instance = null;
private HelloWorld() {
}
public static HelloWorld getInstance() {
if (instance == null) {
instance = new HelloWorld();
}
return instance;
}
public void sayHello() {
System.out.println("hello world!!");
}

public static void sayHello2() {
    System.out.println("hello world 222 !!");
}

}

2.测试类:
public class Test {
public static void main(String[] args) throws Exception {
try {
Class class1 = Class.forName("com.james.HelloWorld");
Object classObject = class1.newInstance();
Method method = class1.getMethod("sayHello");
method.invoke(classObject);
} catch (Exception e) {
e.printStackTrace();
}
}
}

3.运行结果报错:
java.lang.IllegalAccessException: Class com.james.Test can not access a member of class com.james.HelloWorld with modifiers "private"
at sun.reflect.Reflection.ensureMemberAccess(Reflection.java:65)
at java.lang.Class.newInstance0(Class.java:349)
at java.lang.Class.newInstance(Class.java:308)
at com.james.Test.main(Test.java:43)

最后问题来了:这样"Object classObject = class1.newInstance();" new 一个实例肯定会出错的.现在有没有方法,通过这种反射的机制调用到"sayHello()"方法,大家帮我出出主意,先谢谢大家了.

Answer 1

可以：
[code="java"]
public final class HelloWorld
{
private static HelloWorld instance = null;

private HelloWorld()
{
}

public static HelloWorld getInstance()
{
    if (instance == null)
    {
        instance = new HelloWorld();
    }
    return instance;
}

public void sayHello()
{
    System.out.println("hello world!!");
}

public static void sayHello2()
{
    System.out.println("hello world 222 !!");
}

static class Test
{
    public static void main(String[] args) throws Exception
    {
        try
        {
            Class class1 = Class.forName("HelloWorld");
            Constructor[] constructors = class1.getDeclaredConstructors();
            AccessibleObject.setAccessible(constructors, true);
            for (Constructor con : constructors)
            {
                if (con.isAccessible())
                {
                    Object classObject = con.newInstance();
                    Method method = class1.getMethod("sayHello");
                    method.invoke(classObject);
                }
            }

        }
        catch (Exception e)
        {
            e.printStackTrace();
        }
    }
}

}
[/code]
effective java中第三条就说了这种方式。还强调枚举才是单例的王道。