commandfactory.java

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package ui;
import exception.NoExistsCommandException;
/**
 * 用于生产命令对象的工厂
 * @author zouhao
 */
public class CommandFactory {
    private static CommandFactory instance = null;
    /**
     * 此方法是为了实现CommandFactory的Singleton
     * @return
     */
    public static synchronized CommandFactory getInstance() {
        if (instance==null)
        {
            instance=new CommandFactory();
        }
        return instance;
    } 
    /**
     * 实现命令选择并动态生成相应对象
     * @param which 选择输入
     * @return 生成的命令对象
     */
public static Command factory(String which)
    {
        try{
            if (which.equalsIgnoreCase("register"))
            {
                return new RegisterCommand();
            }
            else if (which.equalsIgnoreCase("add"))
            {
                return new AddCommand();
            }
            else if (which.equalsIgnoreCase("delete"))
            {
                return new DeleteCommand();
            }
            else if (which.equalsIgnoreCase("query"))
            {
                return new QueryCommand();
            }
            else if (which.equalsIgnoreCase("clear"))
            {
                return new ClearCommand();
            }
            else if (which.equalsIgnoreCase("batch"))
            {
                return new BatchCommand();
            }
            else if (which.equalsIgnoreCase("help"))
            {
                return new HelpCommand();
            }
            else
            {
               throw new NoExistsCommandException();
            }
        }
        catch(NoExistsCommandException e){}
        return null;
    }

}