regsingleton.java

来自「《Java与模式》一书的源代码」· Java 代码 · 共 55 行

package com.javapatterns.singleton.demos;

import java.util.HashMap;

public class RegSingleton
{
    private static HashMap mRegistry = new HashMap();

    static
    {
        RegSingleton x = new RegSingleton();
        mRegistry.put(x.getClass().getName(), x);
    }

    protected RegSingleton() { }

    public static RegSingleton getInstance(String aName)
    {
        String name = aName;
        if (name == null)
        {
            name = "com.javapatterns.singleton.demos.RegSingleton";
        }

        System.out.println("From RegSingleton: requesting for " + name);

        if (mRegistry.get(name) == null)
        {
            try
            {
                mRegistry.put(name, Class.forName(name).newInstance());
            }
            catch (ClassNotFoundException e)
            {
                System.out.println("Class " + name + " is not found.");
            }
            catch (InstantiationException e)
            {
                System.out.println("Class " + name + " can not be instantiated.");
            }
            catch (IllegalAccessException e)
            {
                System.out.println("Class " + name + " can not be accessed.");
            }
        }
        return (RegSingleton)(mRegistry.get(name));
    }

    public String about()
    {
        return "Hello, I am RegSingleton.";
    }

}