如何从同一个类中的另一个方法调用一个方法（java）

Question

我一直在尝试通过阅读“Java 如何对早期对象进行编程”来了解如何从同一类的另一个方法中调用方法。

此刻我完全迷失了，书中使用的类比让我很容易想象正在发生的事情。但是，将其转换为代码具有挑战性。

我已经尝试了很多次来解决这个问题并且已经走到了这一步： P.S. 为了简单起见，我排除了我认为对我的问题不重要的代码...

import java.util.Scanner;

public class BuyAHouseInc
{
    private int housePrice;
    private int amountOfHouses;
    private int houseCounter;

    // method to enter the amount of houses on sale
    public void setAmountOfHouses()
    {
        // do stuff etc.
    }

    // method that sets the house price
    public void setHousePrice()
    {
        // do stuff etc.

        calculateFees(this.housePrice); // this is where I'm not sure...
    }

    //method to calculate fees and taxes
    public void calculateFees(int housePrice) // does this receive this.housePrice?
    {
      // do some stuff
    }

测试代码：

public class BuyAHouseIncTester
{
    public static void main(String[] args)
    {
        BuyAHouseInc client1 = new BuyAHouseInc("John","Doyle","15 Newton Drive\nDublin 5\n", 550000) // Create object 
        // set amount of houses on sale to client 1
        client1.setAmountOfHouses(); 

        // set house price for each of the houses added to database
        client1.setHousePrice();
    }
}

在另一个方法中调用一个方法的代码是什么？是否调用了每个单独房价的值？

Answer 1

您可以简单地调用calculateFees(housePrice);，因为在调用点唯一可见的housePrice 变量是instance variable private int housePrice;

假设您有一个 constructor 调用来根据您创建 BuyAHouseInc 的方式设置 housePrice

//费用和税金的计算方法 public void calculateFees(int housePrice) // 这会收到 this.housePrice 吗？ { // 做一些事情 }

是的，这将收到通过calculateFees(housePrice); 传递的housePrice

calculateFees(int housePrice) 上面定义的局部变量只在calculateFees(int housePrice){...}方法内部可见

Passing Information to a Method or a Constructor

更新：基于 cmets，您需要更新您的 setter 以传递房价

public void setHousePrice(int housePrice)
    {
        this.housePrice = housePrice;

        calculateFees(this.housePrice); 
    }

Answer 2

是的，你的假设是正确的。

但是，有一些重要的事情需要注意。这段代码：

public void setHousePrice()
{
    // do stuff etc.

    calculateFees(this.housePrice); // <---This probably doesn't do what you think it does
}

// No. This doesn't receive this.housePrice. It receives the VALUE of this.housePrice. 
// It's a completely new variable
public void calculateFees(int housePrice) .
{
  // do some stuff
}

Java 是按值传递的。您正在传递 housePrice 的值，但并未修改原始 housePrice。

因此，如果您“做一些事情”并修改传入的 housePrice 变量，除非您在 calculateFees 中设置 housePrice，否则这些更改不会保存。

在这种情况下，最好通过 getter/setter 来操作任何成员变量。顺便说一句，约定是 setter 应该总是取值。这不是任意的，因为许多库都依赖于 set/get 方法以某种方式发挥作用。

我已将上述答案编辑得更清楚。

Answer 3

如果我错了，请纠正我，但这是一个可能的解决方案：

public void setHousePrice(int price)
{


    calculateFees(price); 
}


public void calculateFees(int housePrice) 
{
  // stuff with housePrice
}

然后做

variable.setHousePrice(variable.getHousePrice);

Answer 4

public class BuyAHouseInc {
    private double housePrice;
    private int amountOfHouses;
    private int houseCounter;

    public BuyAHouseInc(double housePrice, int amountOfHouses, int houseCounter) {
        this.housePrice = housePrice;
        this.amountOfHouses = amountOfHouses;
        this.houseCounter = houseCounter;
    }

    // method that sets the house price
    public void generateHousePrice() {
        // do stuff etc.
        // you could also put the logic in the set method... Had to change the method name to 
        // generate as the getters and setter where created and the setter method is named
        // exactly like your previous method
        calculateFees(housePrice); // this is were I'm not sure...
    }

    // method to calculate fees and taxes
    public void calculateFees(double housePrice) // does this receive
                                                    // this.housePrice?
    {
        // do some stuff
    }

    public double getHousePrice() {
        return housePrice;
    }

    public void setHousePrice(double housePrice) {
        this.housePrice = housePrice;
    }

    public int getAmountOfHouses() {
        return amountOfHouses;
    }

    public void setAmountOfHouses(int amountOfHouses) {
        this.amountOfHouses = amountOfHouses;
    }

    public int getHouseCounter() {
        return houseCounter;
    }

    public void setHouseCounter(int houseCounter) {
        this.houseCounter = houseCounter;
    }

    @Override
    public String toString() {
    return "BuyAHouseInc [housePrice=" + housePrice + ", amountOfHouses=" + amountOfHouses + ", houseCounter="
            + houseCounter + "]";
}


}

将两个类分开在不同的文件中。需要指出的另一件事是使用 double 作为价格而不是 int。 您还必须创建 getter 和 setter 才能获取和设置您的属性。 您还必须在类中添加一个构造函数。然后您可以在 main 中创建该类的实例并调用其方法。 主要方法如下所示。

public class Main {

    public static void main(String... args) {
        BuyAHouseInc test = new BuyAHouseInc(200000, 4, 2);
        test.setAmountOfHouses(6); // changed from 4 to 6
        test.generateHousePrice();
        test.calculateFees(test.getHousePrice());
        test.toString();

    }
}

希望你觉得这很有帮助，祝你好运！我已经编辑了代码并添加了 toString 方法以将信息输出为字符串。