Java 如何添加到计算器的当前值方法

我正在创建一个内存计算器。在我的代码中，我有一个current value方法，当操作符决定加、减、乘等时，需要它返回一个新值。。。我不知道如何更改当前值字段。当我选择向当前值添加一个数字时，该值与以前的值相同，即0

头等舱

import java.util.Scanner;

public class MemoryCalculator {
private double currentValue;

    public static int displayMenu() {
        Scanner input = new Scanner(System.in);

        System.out.println("Menu");
        System.out.println("1. Add ");
        System.out.println("2. Subtract ");
        System.out.println("3. Multiply ");
        System.out.println("4. Divide ");
        System.out.println("5. Clear ");
        System.out.println("6. End");
        System.out.println("Please choose which math operation to perform, or press 6 to quit.");

        int selection = input.nextInt();

        return selection;

    }
    public static double getOperand(String prompt) {
        Scanner input = new Scanner(System.in);
        System.out.println(prompt);

        double operand = input.nextDouble();

        return operand;

    }
    public double getCurrentValue() {
        this.currentValue = currentValue;
        return currentValue;

    }
    public void add(double operand2) {
        this.currentValue = getCurrentValue() + operand2;
        getCurrentValue();

    }
    public void subtract(double operand2) {

    }
    public void multiply(double operand2) {

    }
    public void divide(double operand2) {

    }
    public void clear() {

    }


}

二等司机

public class MemoryCalculatorDriver {

public static void main(String[] args) {
    double operand2 = 0;

    MemoryCalculator CalcObj = new MemoryCalculator();

    System.out.println(CalcObj.getCurrentValue());
    int selection = CalcObj.displayMenu();

    if(selection == 1) {
        System.out.println(CalcObj.getOperand("What would you like the second number to be"));

        CalcObj.add(operand2);

        System.out.println(CalcObj.getCurrentValue());

    }else if (selection == 2) {
        System.out.println(CalcObj.getOperand("What would you like the second number to be"));

        CalcObj.subtract(operand2);

        System.out.println(CalcObj.getCurrentValue());

    }else if (selection == 3) {
        System.out.println(CalcObj.getOperand("What would you like the second number to be"));

        CalcObj.multiply(operand2);

        System.out.println(CalcObj.getCurrentValue());

    }else if (selection == 4) {
        System.out.println(CalcObj.getOperand("What would you like the second number to be"));

        CalcObj.divide(operand2);

        System.out.println(CalcObj.getCurrentValue());

    }else if (selection == 5) {
        CalcObj.clear();

        System.out.println(CalcObj.getCurrentValue());

    }else if (selection == 6) {
        System.out.println("Goodbye");
    }


}

}

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我可以从用户那里获得选择输入，并且可以从用户那里获得第一个数字。当我选择选项1“添加”时，用户可以输入数字，但数字没有添加到当前值

通过此方法返回值

公共静态双GetOperator（字符串提示）

但在何处使用返回值

一定是这样的:

if(selection == 1) {
        operand2 = CalcObj.getOperand("What would you like the second number to be"));
        CalcObj.add(operand2);
        System.out.println(CalcObj.getCurrentValue());

        // your code like this...
}

---

public double getCurrentValue（）{return this.currentValue；}不需要该代码的其余部分。public void add（double operans2）{this.currentValue+=operans2；System.out.println（“新值：+getCurrentValue（））；}当前值永远不会被打印。可能会删除打印，因为它在其他方法中。