一、簡單工廠模式:

實質是由一個工廠類根據傳入的引數，動態決定應該建立哪一個產品類（這些產品類繼承自一個父類或介面）的例項。簡單工廠模式的建立目標，所有建立的物件都是充當這個角色的某個具體類的例項。

二、場景

使用Java面嚮物件語言實現一個計算機控制檯程式，要求輸入兩個數和運算子號，得到結果。
為了使程式達到易擴充套件，易維護，易複用且靈活的目的，本程式將使用到面向物件程式設計思想的三大特性：封裝、繼承和多型，以及簡單工廠模式

三、程式程式碼

程式共有七個類：

MyOperation.java

public class MyOperation {

    private
 
 double numberA;
    private double numberB;
    public double getNumberA() {
        return numberA;
    }
    public void setNumberA(double numberA) {
        this.numberA = numberA;
    }
    public double getNumberB() {
        return numberB;
    }
    public void setNumberB(double numberB) {
        this
 
.numberB = numberB;
    }

    public double getResult() throws Exception {
        double result=0;
        return result;
    }
}

OperaAdd.java

public class OperaAdd extends MyOperation {

    @Override
    public double getResult() {
        double result=0;
        result=this.getNumberA()+this
 
.getNumberB();
        return result;
    }
}

OperaSub.java

public class OperaSub extends MyOperation {

    @Override
    public double getResult() {

        return this.getNumberA()-this.getNumberB();
    }
}

OperaMul.java

public class OperaMul extends MyOperation {

    @Override
    public double getResult() {

        return this.getNumberA()*this.getNumberB();
    }
}

OperaDiv.java

public class OperaDiv extends MyOperation{

    @Override
    public double getResult() throws Exception {
        if(this.getNumberB()==0){
            throw new Exception("除數不能為0");
        }
        return this.getNumberA()/this.getNumberB();
    }
}

OperationFactory.java

public class OperationFactory {

    public static MyOperation createOperation(String operate){
        MyOperation operation=null;
        switch (operate) {
        case "+":
            operation=new OperaAdd();
            break;

        case "-":
            operation=new OperaSub();
            break;

        case "*":
            operation=new OperaMul();
            break;

        case "/":
            operation=new OperaDiv();
            break;
        default:
            operation=new MyOperation();
            break;
        }
        return operation;
    }
}

Calculator.java

import java.util.Scanner;

public class Calculator {

    /**
     * @Title: main
     * @Description: 計算器
     * @param args   
     * @return void    返回型別
     * @throws
     */
    public static void main(String[] args) {
        MyOperation operation=null;
        try {
            System.out.println("請輸入數字A:");
            double numberA=Double.valueOf(new Scanner(System.in).nextLine());
            System.out.println("請輸入運算子:");
            String operaString=new Scanner(System.in).nextLine();
            System.out.println("請輸入數字B:");
            double numberB=Double.valueOf(new Scanner(System.in).nextLine());
            operation=OperationFactory.createOperation(operaString);
            operation.setNumberA(numberA);
            operation.setNumberB(numberB);
            System.out.println("結果是："+operation.getResult());

        } catch (NumberFormatException e) {
            System.out.println("只能輸入數字");
        } catch (Exception e) {
            System.out.println(e.getMessage());
        }


    }

}