单态设计模式

package com.yanek.test;

public interface UserManager {

public abstract void addUser();

}

package com.yanek.test;

public class UserManagerImpl implements UserManager {

public void addUser() {

System.out.println("hello world!");

}

}

package com.yanek.test;

public class UserManagerFactory {

private static UserManager userManager;

private UserManagerFactory()
{
}

public synchronized static UserManager getInstance()
{
if (!initialized)
doInitialize();
return userManager;
}

private static boolean initialized = false;

private static synchronized void doInitialize()
{
if (!initialized)
{
userManager = new UserManagerImpl();
initialized = true;
}
}

/**
* @param args
*/
public static void main(String[] args) {


UserManager um1=UserManagerFactory.getInstance();

UserManager um2=UserManagerFactory.getInstance();

UserManager um3=UserManagerFactory.getInstance();

System.out.println("um1="+um1);
System.out.println("um2="+um2);
System.out.println("um3="+um3);

um1.addUser();
um2.addUser();
um3.addUser();

}

}