这是我的程序。只要有this.pizzaorder[i].clone()
或this.pizzaorder[count].clone()
,我就会收到一个错误,说Object
类型的Clone()
不可见。有什么帮助吗?
import java.text.NumberFormat;
public class PizzaOrder {
NumberFormat moneyFormatter = NumberFormat.getCurrencyInstance();
public int TotalNoOfPizzas, keep;
//declaring the variables needed for this class
public double totalcost;
Pizza[] pizzaorder = new Pizza[TotalNoOfPizzas];
int i;
public PizzaOrder() {
//constructor to initialize all the varibales
this.TotalNoOfPizzas = 0;
this.totalcost = 0.0;
for ( i = 1; i <= pizzaorder.length; i++ ) {
pizzaorder[i] = null; }
}
public PizzaOrder( PizzaOrder keep ) {
// copy constructor
for ( i = 1; i <= pizzaorder.length; i++) {
this.pizzaorder[i] = this.pizzaorder[i].clone(); }
this.TotalNoOfPizzas = keep.TotalNoOfPizzas;
this.totalcost = keep.totalcost; }
public int getTotalNoOfPizzas() {
//using Accessor to get the number of pizzas
return this.TotalNoOfPizzas; }
public void setTotalNoOfPizzas( int TotalNoOfPizzas1 ) {
//using mutators to set the number of pizzas
this.TotalNoOfPizzas = TotalNoOfPizzas1; }
public Pizza getPizza ( int pizzas) {
//using Accessor to get the size and toppings for pizza 1
return (this.pizzaorder[pizzas]); }
public void setPizza(Pizza tempPizza, int count) {
this.pizzaorder[count].clone(); }
public double getTotalCost() {
return(this.totalcost); }
public void setTotalCost(double totalcost1) {
this.totalcost = totalcost1; }
public double calcTotal() {
//calculating the total cost
double totalcostoford = 0;
for (i = 1; i <= pizzaorder.length; i++) {
totalcostoford += this.pizzaorder[i].calcCost(); }
return totalcostoford; }
public String tostring() {
String pizzaDescription;
pizzaDescription = "n Order No.:" + this.pizzaorder;
pizzaDescription +="nTotal No. of pizza's ordered:" + TotalNoOfPizzas;
for ( i = 0; i <= pizzaorder.length; i++ ) {
pizzaDescription += "n" + i + ". Pizza" +
pizzaorder[i].getPizzaDescription(); }
pizzaDescription += "n" + moneyFormatter.format(this.getTotalCost()) + "is your
total price.";
return pizzaDescription;
}
}
您最初的问题是,如果您希望克隆公开可见,则需要在类中声明一个public
克隆方法。
但仅仅这样做是不够的:
public Object clone() {
try {
return super.clone();
} catch (Exception e) {
return null;
}
}
这有两个问题。 首先,捕获异常并返回此类null
违反了clone()
应如何行为的合同。 阅读 javadoc for Object.clone()
以了解它应该如何表现。 在发生故障时没有理由返回null
。 您应该引发异常,或允许现有异常传播。
javadoc 也解释了您出现异常的原因。 您依赖于对象的本机克隆机制。 但是,仅当您尝试克隆的类实现了Cloneable
标记接口时,该机制才有效。 如果没有,则调用super.clone()
将引发CloneNotSupportedException
。
最后,我要指出,您需要小心克隆。 一方面,它可能很昂贵。 另一方面,使用本机克隆机制进行克隆并不总是为您的应用程序做"正确的事情"。 此机制仅为您提供浅层副本;即,它不会复制您正在克隆的对象的"组件"对象。
要克隆一个类,你需要覆盖clone()方法,你需要把代码放在那里,创建你的类的新实例并将另一个类的成员变量复制到它,然后返回新实例。
我建议不要使用clone
而是使用复制构造函数。
在Pizza
类中,添加一个复制构造函数:
class Pizza {
private final sometype some field;
...
Pizza(Pizza that) {
this.somefield = that.somefield;
}
...
然后代替
this.pizzaorder[i] = keep.pizzaorder[i].clone();
做
this.pizzaorder[i] = new Pizza(keep.pizzaorder[i]);
恕我直言,这更干净,更容易理解。