命令模式undo/redo实例计算器

package JiSuan;

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 JiSuan;

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 JiSuan;

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 JiSuan;

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--;
	}
}
}