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--;
    }
}
}