用JAVA面向对象写计算器（且避免无效输入）

先放目录结构

Operation类中封装了a,b两个运算数，以及得到运算结果的方法

package jisuanqi;

public class Operation {
	private double a;
	private double b;
	public double getA() {
		return a;
	}
	public void setA(double a) {
		this.a = a;
	}
	public double getB() {
		return b;
	}
	public void setB(double b) {
		this.b = b;
	}
	public double getResult(){
		double result=0;
		return result;
	}
}

以下是加减乘除四个类：分别继承了Operation父类，每个类都重写了Operation中的getResult方法，将运算数进行不同的运算

package jisuanqi;

public class OperationAdd extends Operation{
	public double getResult(){
		double result=0;
		result=getA()+getB();
		return result;
	}
}

package jisuanqi;

public class OperationSub extends Operation{
	public double getResult(){
		double result=0;
		result=getA()-getB();
		return result;
	}
}

package jisuanqi;

public class OperationMul extends Operation{
	public double getResult(){
		double result=0;
		result = getA()*getB();
		return result;

	}
}

package jisuanqi;

public class OperationDiv extends Operation{
	public double getResult(){
		double result=0;
		if(getB()==0){
			System.out.println("除数不能未为0");
		}
		result = getA()/getB();
		return result;
	}
}

然后我把运算符写成了全局变量

package jisuanqi;

public class Global {
	public Operation ope;
}

根据输入的符号，用工厂模式判断一下要调用哪个类进行运算

package jisuanqi;

public class OperationFactory {
	public static Operation createOperationFactory(String operation){
		Operation ope = null;
		switch(operation){
			case "+":
				ope = new OperationAdd();
				break;
			case "-":
				ope = new OperationSub();
				break;
			case "*":
				ope = new OperationMul();
				break;
			case "/":  
				ope = new OperationDiv();
				break;
			default:
				System.out.println("运算符错误，请重新输入");
				ope = new View().fuhao();
				break;
		}
		return ope;
	}
}

然后就该写输入了，对输入的运算数a,b,以及运算符判断是否合法，用正则表达式进行判断

package jisuanqi;

import java.util.Scanner;

public class View {
//	public static Operation ope = null;
	
	public static String total(){
		Scanner scanner = new Scanner(System.in);
		String operator =  scanner.next();
		return operator;
	}
	
	public static Operation fuhao(){
		System.out.println("输入运算符");
        return  new Biz().fuhaoObject(total());
    }
	
	public static void num1(Operation ope){
		System.out.println("输入运算数a");
        Biz biz = new Biz();
        String num1 = total();
        if(biz.matches(num1)){
        	double a1 = Double.valueOf(num1);
        	ope.setA(a1);
        }else{
        	System.out.println("您输入的运算数有误，请重新输入");
        	num1(ope);
        }
    }
	
	public static void num2(Operation ope){
		Scanner scanner = new Scanner(System.in);
		System.out.println("输入运算数b");
//        String operator =  scanner.next();
        Biz biz = new Biz();
        String num2 = total();
        if(biz.matches(num2)){
        	double a2 = Double.valueOf(num2);
        	ope.setB(a2);
        }else{
        	System.out.println("您输入的运算数有误，请重新输入");
        	num2(ope);
        }
    }
}

Biz类中封装了对输入进行判断的正则表达式的方法

package jisuanqi;

public class Biz {
	public static boolean matches(String a){
		if(a.matches("^[-+]?(([0-9]+)(.)?|(.)?)$")){
			return true;
		}else{
			return false;
		}
		
	}
	
	public static Operation fuhaoObject(String operator){
		Operation ope = new OperationFactory().createOperationFactory(operator);
		return ope;
	}
	
	public static void jieguo(Operation ope){
		double result = ope.getResult();
		System.out.println("输出的结果为 ");
		System.out.println(result); 
	}
}

然后就是主方法了：run类

package jisuanqi;
import java.util.Scanner;

//import javax.swing.text.View;
public class Run {
	public static void main(String[] args) {
		
		View v = new View();
		Operation ope = null;
		ope = v.fuhao();
		v.num1(ope);
		v.num2(ope);
		double result = ope.getResult();
		System.out.println("输出的结果为 ");
		System.out.println(result);
	}
}

该计算器输入有误会自动提示让重新输入，直至输入正确会进行运算