我正在学校做一项练习。我必须创建一个收银机并且需要使用数组。我遇到的问题是当我想从数组中删除最后一个元素时。例如，数组的最大容量是 42，我添加例如 items = { 2, 24, 65}。如果我打印数组，我会得到类似输出 {2,24,65,0,0,0 ,0,0,0...} 直到 42。如果我没有使用默认构造函数，那么我的代码似乎可以正常工作。但是，如果我在创建对象时不提供任何参数，则它采用数组 42 的默认值不起作用。我的意思是我可以理解，从数组中删除最后一个 0，它的长度就会变成 41，但我要删除的项目位于索引 0 1 或 2 处，具体取决于我添加了多少项目。所以我的问题是如何删除最后添加的项目。例如，如果我有 3 个项目，并且我调用该方法 3 次，那么我应该没有更多的项目。
import java.util.Arrays;
public class CashRegisterP816
{
// TODO: insert declarations of instance variables
private int itemCount ;
private int capacity ;
private double[] items = new double[capacity];
/**
* Constructor for objects of class CashRegisterP816
*
* @param capacity the maximal number of items the cash register can store
*/
public CashRegisterP816()
{
this.items = new double[42];
}
/**
* Constructor for objects of class CashRegisterP816
* (with the default capacity)
*/
public CashRegisterP816(int capacity)
{
this.items = new double[capacity];
this.capacity=capacity;
}
/**
* Gets the number of items in the current sale
*
* @return the item count
*/
public int getCount()
{
return itemCount;
}
/**
* Gets the price of all items in the current sale
*
* @return the total price
*/
public double getTotal()
{
double sum = 0;
for(double pricePerItem : items){
sum=sum+pricePerItem;
}
return sum;
}
/**
* Clears the cash register before the next sale
*/
public void clear()
{
// TODO:
itemCount = 0;
for (int i=0; i<items.length; i++)
{
items[i] = 0;
}
}
/**
* Adds an item to the cash register
*
* @param price the price of the item
*/
public void addItem(double price)
{
if(price > 0 && itemCount < capacity)
{
this.items[itemCount] = price;
itemCount++;
}
}
/**
* Cancels the last item in the cash register
*/
public void cancelLast()
{
if(itemCount != 0)
{
this.itemCount--;
this.items=Arrays.copyOf(items, items.length-1);
}
}
/**
* Prints out all the items in the current sale
*/
public void displayAll()
{
for(int i =0; i<items.length; i++){
//Print the item array
System.out.println(items[i]);
}
}
}
这是测试类。除了以默认大小 42 创建的对象 r3 的最后一个实例之外，一切都正常。
public class CashRegisterP816Test
{
public static void main(String[] args)
{
CashRegisterP816 r1 = new CashRegisterP816(3);
r1.addItem(0);
System.out.println("r1.add(0): " + (r1.getCount() == 0 ? "OK" : "FAIL"));
r1.addItem(1.2);
System.out.println("r1.add(1.2): " + (r1.getCount() == 1 ? "OK" : "FAIL"));
r1.addItem(2.3);
System.out.println("r1.add(2.3): " + (r1.getCount() == 2 ? "OK" : "FAIL"));
r1.addItem(-2);
System.out.println("r1.add(-2): " + (r1.getCount() == 2 ? "OK" : "FAIL"));
r1.addItem(1.4);
System.out.println("r1.add(1.4): " + (r1.getCount() == 3 ? "OK" : "FAIL"));
System.out.println("r1.add(1.4): " + (r1.getTotal() == 4.9 ? "OK" : "FAIL"));
CashRegisterP816 r2 = new CashRegisterP816(5);
r2.addItem(3);
r2.addItem(5.2);
r2.addItem(6);
r2.addItem(7);
System.out.println("r2.add(3, 5.2, 6, 7): " + (r2.getCount() == 4 ? "OK" : "FAIL"));
System.out.println("r2.add(3, 5.2, 6, 7): " + (r2.getTotal() == 21.2 ? "OK" : "FAIL"));
r2.addItem(9);
System.out.println("r2.add(9): " + (r2.getCount() == 5 ? "OK" : "FAIL"));
System.out.println("r2.add(9): " + (r2.getTotal() == 30.2 ? "OK" : "FAIL"));
r2.addItem(7);
System.out.println("r2.add(7): " + (r2.getCount() == 5 ? "OK" : "FAIL"));
System.out.println("r2.add(7): " + (r2.getTotal() == 30.2 ? "OK" : "FAIL"));
System.out.println("r1: " + (r1.getCount() == 3 ? "OK" : "FAIL"));
System.out.println("r1: " + (r1.getTotal() == 4.9 ? "OK" : "FAIL"));
r1.cancelLast();
System.out.println("r1.cancelLast: " + (r1.getCount() == 2 ? "OK" : "FAIL"));
System.out.println("r1.cancelLast: " + (r1.getTotal() == 3.5 ? "OK" : "FAIL"));
r1.cancelLast();
System.out.println("r1.cancelLast: " + (r1.getCount() == 1 ? "OK" : "FAIL"));
System.out.println("r1.cancelLast: " + (r1.getTotal() == 1.2 ? "OK" : "FAIL"));
r1.cancelLast();
System.out.println("r1.cancelLast: " + (r1.getCount() == 0 ? "OK" : "FAIL"));
System.out.println("r1.cancelLast: " + (r1.getTotal() == 0 ? "OK" : "FAIL"));
r2.clear();
System.out.println("r1.cancelLast: " + (r2.getCount() == 0 ? "OK" : "FAIL"));
System.out.println("r1.cancelLast: " + (r2.getTotal() == 0 ? "OK" : "FAIL"));
CashRegisterP816 r3 = new CashRegisterP816();
r3.addItem(2.99);
System.out.println("r3.addItem(2.99): " + (r3.getTotal() == 2.99 ? "OK" : "FAIL"));
r3.cancelLast();
System.out.println("r3.cancelLast: " + (r3.getTotal() == 0 ? "OK" : "FAIL"));
r1.displayAll();
r2.displayAll();
r3.displayAll();
}
}
最佳答案
How do I delete the last item from a fixed array in java
array[array.length-1]=null 将把最后一个元素设置为 null(或者在数字数组的情况下使用 0)。这不会缩小数组，因为 Java 中的数组始终具有固定大小
关于java - 如何从java中的固定数组中删除最后一项，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/60562291/