我试图让一个类从另一个类返回一个字符串,尽管我得到的返回值为空。我有一个 set 方法,可以在原始类中设置字符串,但是当在第二个类中调用该方法时,我得到 null 返回。
这是第一堂课;
public class IceCream
{
// instance variables - replace the example below with your own
private String flavour;
public static double price;
/**
* Constructor for objects of class IceCream
*/
public IceCream()
{
// initialise instance variables
String flavour = getFlavour();
price = 0.50;
}
/**
* Gets price in pence.
*
*
* @returns the price of the ice cream.
*/
public static double getPrice()
{
// put your code here
return price;
}
public int getScoops()
{
return scoop;
}
public void setPrice(int newPrice)
{
price = newPrice;
}
public void setScoops(int scoopNumber)
{
scoop = scoopNumber;
}
public double totalCost()
{
double cost;
cost = scoop * price;
return cost;
}
public String getFlavour()
{
return flavour;
}
public void setFlavour(String whatFlavour)
{
flavour = whatFlavour;
}
}
第二个类,我尝试在 sundaeDetails 方法的 println 中调用我在 setFlavour 方法中输入的字符串。
import java.util.ArrayList;
/**
* Write a description of class Sundae here.
*
* @author (your name)
* @version (a version number or a date)
*/
public class Sundae
{
// instance variables - replace the example below with your own
private IceCream flavour;
private Topping SundaeTopping;
private int scoops;
/**
* Constructor for objects of class Sundae
*/
public Sundae()
{
flavour = new IceCream();
SundaeTopping = new Topping();
scoops = 0;
}
/**
* Set scoop number.
*/
public void setScoops(int scoopNumber)
{
scoops = scoopNumber;
}
/**
* Return scoop variable.
*/
public int getScoops()
{
return scoops;
}
/**
* Get the price of the sundae.
*/
public void getPrice()
{
double cost;
double scoopPrice = scoops * IceCream.getPrice();
if ( scoops > 0) {
cost = scoopPrice * Topping.getToppingPrice();
System.out.println("Cost of Sundae: " + cost);
}
else {
System.out.println("Need to have a scoop of ice cream in your Sundae.");
}
}
/**
* Return the details of the sundae; price, flavour, scoops etc.
*/
public void sundaeDetails()
{
System.out.println("You have " + scoops + " scoops of " + flavour.getFlavour() + "ice cream");
}
}
在 IceCream 类构造函数中,您有:
String flavour = getFlavour()
您创建了一个局部变量,而不是对实例属性的引用。 getFlavour() 方法返回您从未设置的属性实例,因此它为 null。你应该在构造函数中有这样的东西:
this.flavour = "default value";
或者在构造函数头设置一个风味参数:
public IceCream(String flavour) {
this.flavour = flavour;
(...)
}
并称其为:
IceCream chocolat = new IceCream(" chocolat");
如果您想改变口味,请使用设置器。
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