将构造函数参数传递给方法 JAVA

Question

我正在学习软件开发课程，目前我正在学习 Java。

我正在处理的程序（不用担心，我可以得到外部帮助）给我带来了问题，而且问题是我不明白他们如何措辞手头的任务.这就是我所在的位置。

我需要做的是创建一个带有两个变量的构造函数，然后将其中一个参数传递给一个方法。类和构造函数称为Order()，方法称为testQuantity。这是我不明白的。第一个参数productName 的值通过代码this.productName = productName; 分配给实例变量productName，但对于第二个参数quantity，它不会要求我将值分配给实例变量quantity，而是“数量参数将被传递给 testQuantity 方法。”

好的，这是我目前的代码，它还远未完成，还有四个其他类我还没有开始。也随时指出您在此过程中发现的任何问题。提前感谢您的帮助。

package JaveGUIPrototype;
import java.util.Arrays;
/**
*
* @author User
*/
public class Order {
private String productName;
private double price;
private int discount;
private int quantity;
private double total;
private String message;
private boolean isDiscounted;
private boolean isValidOrder;
private static int orderNum = 0;

public Order() {
    // sets validity to false, sets message, increments orderNum by 1
    isValidOrder = false;
    message = "**ERROR**: Order number cannot be totalled as no details have been supplied";
    orderNum = orderNum + 1;
}

public Order(String productName, int quantity) {
    // sets productName variable to productName parameter value
    this.productName = productName;
    this.quantity = quantity;
}




public void testQuantity() {
    // tests the value of the quantity variable
    // quantity is 0 or less, order isn't valid, message explains why
    if(quantity <=0){
        isValidOrder = false;
        message = "**ERROR**: Invalid quantity. Quantity cannot be 0 or less";
    }
    // quantity is greater than 1000, order isn't valid, message explains why
    else if(quantity >1000) {
        isValidOrder = false;
        message = "**ERROR**: Invalid quantity. Quantity cannot be greater than 1000";
    }
    // quantity is valid, quantity instance variable assigned value of parameter variable
    else {
        this.quantity = quantity;
    }
}

public void testDiscount(int discount) {
    // tests the value of the discount variable

    // discount is 0 or less, order isn't valid, message explains why
    if(discount <=0) {
        isValidOrder = false;
        message = "**ERROR**: The discount rate cannot be lower than or equal to 0";
    }
    // discount is greater than 50, order isn't valid, message explains why
    else if(discount >50) {
        isValidOrder = false;
        message = "**ERROR**: The discount rate cannot be greater than 50";
    }
    // discount is valid, discount instance variable assigned value of parameter variable
    // isDiscounted variable set to true
    else {
        this.discount = discount;
        isDiscounted = true;
    }
}

String[] products = {"Compass",
                    "Eraser",
                    "Pen",
                    "Pencil",
                    "Pencil Case",
                    "Ruler",
                    "Scissors"};
double[] prices = {4.5, 0.5, 0.3, 0.6, 10, 0.3, 1.2, 2.5};
int indexPos;
double indexVal;

public void getPrice(String productName) {
    // searches products array by value of productName variable
    indexPos = Arrays.binarySearch(products, productName);
    // tests for validity of result
    if (indexPos >-1) {
        // assigns value of prices array by index position
        indexVal = prices[indexPos];
        // assigns prices array value to price variable
        price = indexVal;
    }
    else {
        // product name not valid, not a valid order, message explains why
        isValidOrder = false;
        message = "**ERROR**: Invalid product name";
    }
}

public void calculate() {
    // tests for validity
    if(isValidOrder == true) {
        // tests for discount
        if(isDiscounted == false) {
            // equats total without discount
            total = quantity * price;
        }
        else {
            // equats total with discount
            total = quantity * price - quantity * price * (discount/100);
        }
    }
}

public String getOrderDetails() {
    //tests for validity
    if(isValidOrder == true) {
        //tests for discount
        if(isDiscounted == false) {
            // sets non discounted message details
            message = "Order number: " + orderNum +
                    "Product name: " + productName +
                    "Product price: $" + price +
                    "Order quantity: " + quantity +
                    "Total price: $" + total;
        }
        else {
            // sets discounted message details
            message = "Order number: " + orderNum +
                    "Product name: " + productName +
                    "Product price: $" + price +
                    "Order quantity: " + quantity +
                    "Discount: " + discount + "%" +
                    "Total price: $" + total;
        } 
    }

    return message;

}

Answer 1

您可以创建多个构造函数，只要它们具有不同的签名即可。 （不同的参数号，不同的参数类型），但不是返回类型。

你应该阅读更多关于方法重载的信息，但你想：

public Order(String productName, int quantity) {
    // sets productName variable to productName parameter value
    this.productName = productName;
    this.quantity = quantity;
}

public Order(String productName) {
    // sets productName variable to productName parameter value
    this.productName = productName;

}

Answer 2

它没有要求我将值赋给实例变量quantity

那你为什么要这么做？更改testQuantity 以接受参数，并传递构造函数的quantity 参数：

public Order(String productName, int quantity) {
    this.productName = productName;
    testQuantity(quantity);
}

public void testQuantity(int quantity) {
    // Do something with quantity.
    // Copying the original implementation should suffice.
}