命令模式实例计算器

使用命令模式岩石和简单的计算器功能,并允许执行UNDO和REDO

UML图

代码

package 命令模式;

public class Caculator {
private int total;
 
public Caculator() {
	
	this.total = 0;
}
 
public void Operation(char op,int num)
{switch(op)
	{case '+':total+=num;break;
	case '-':total-=num;break;
	case '*':total*=num;break;
	case '/':total/=num;break;
}
System.out.println(op+" "+num+"="+total);
 
}
}

package 命令模式;

public class CalCommand extends Command {
 
	public CalCommand(Caculator cal, char op, int num) {
		super(cal, op, num);
		
	}
 
	@Override
	public void Execute() {
	cal.Operation(op, num);
	}
 
	@Override
	public void UnExecute() {
		cal.Operation(undo(op), num);
 
	}
	private char undo(char op)
	{char undo=' ';
	switch(op)
	{case '+':undo='-';break;
	case '-':undo='+'; break;
	case '*':undo='/';break;
	case '/': undo='*'; break;
	}
	return undo;
	}
 
}

package 命令模式;

public abstract class Command {
	protected Caculator cal;
	protected char op;;
	protected int num;
	
public Command(Caculator cal, char op, int num) {
		
		this.cal = cal;
		this.op = op;
		this.num = num;
	}
public abstract void Execute();
public abstract void UnExecute();
}

package 命令模式;

import java.util.ArrayList;
 
public class User {
private ArrayList<Command>commands=new ArrayList<Command>();
private int count=0;
public void Compute(Command command)
{command.Execute();
count++;
commands.add(command);
 
}
public void Redo(int levels)
{for(int i=0;i<levels;i++)
{if(count<commands.size())
	{count++;
	commands.get(count-1).Execute();
 
}
}
}
public void Undo(int levels)
{for(int i=0;i<levels;i++)
	if(count>0)
	{
		commands.get(count-1).UnExecute();
	count--;
	}
}
}