《面向对象的计算器》

package com.lewang;

import java.util.HashMap;import java.util.Map;

abstract class Operator {    public final String op;

    public Operator(String op) {        this.op = op;    }

    public double op(String lhs, String rhs) {        double a = Double.parseDouble(lhs);        double b = Double.parseDouble(rhs);        return opImpl(a, b);    }

    protected abstract double opImpl(double lhs, double rhs);}

class OperatorAdd extends Operator {    public OperatorAdd() {        super("+");    }

    @Override    public double opImpl(double lhs, double rhs) {        return 0;    }}

class OperatorSub extends Operator {    public OperatorSub() {        super("-");    }

    @Override    public double opImpl(double lhs, double rhs) {        return 0;    }}

class Calculator {    private Map<String, Operator> operatorMap = new HashMap<>();

    public Calculator() {    }

    public Calculator addOperator(Operator operator) {        this.operatorMap.put(operator.op, operator);        return this;    }

    public double calculate(String op, String lhs, String rhs) throws IllegalArgumentException {        if (!this.operatorMap.containsKey(op)) throw new IllegalArgumentException("unknown operator");        return this.operatorMap.get(op).op(lhs, rhs);    }}

public class Main {    public static void main(String[] args) {        Calculator calculator = new Calculator();        calculator.addOperator(new OperatorAdd() {            @Override            public double opImpl(double lhs, double rhs) {                return lhs + rhs;            }        }).addOperator(new OperatorSub() {            @Override            public double opImpl(double lhs, double rhs) {                return lhs - rhs;            }        });        System.out.println(calculator.calculate("+", "1.0", "2.0"));    }}