Question

任务是：编写一个java程序，该程序从用户获取整数输入流并找到它们之间的最小距离流中的两个相邻数字。它应该输出两个相邻数字的索引。

这是代码，我在arraylist中存储了一些数字，然后我拿了arraylist的最后一个索引并尝试创建一个具有相同数量元素的数组

import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;

public class Pr6 
{
public Pr6 ()
{
    Scanner sc = new Scanner (System.in);
    String x = "";
    int Distance =0;
    int Index1 = 0;
    int Index2 = 0;
    List<Integer> AllNum = new ArrayList<>();
    do 
    {
        System.out.println ("Please enter a number");
        int NewNumber = sc.nextInt();
        AllNum.add (NewNumber);
        System.out.println ("Do you want to enter a new number? Enter Y for yes and N for no");
        x = sc.nextLine();
    } while ("Y".equals(x));

    int Index = AllNum.size();
    int [] AllNumArray = new int [Index];

    for (int i = 0; i < Index; i++)
    {
        AllNumArray[i] = AllNum.get(i);
    }

    for (int i = 0; i < Index; i++)
    {
        int NewDistance = AllNumArray[i] - AllNumArray [i+1];
        if (NewDistance > Distance)
        {
            Distance = NewDistance;
            Index1 = i;
            Index2 = i+1;
        }
    }

    System.out.println ("The smallest distance between two neighboring numbers is: " + Distance);
    System.out.println("The first Nnumber is " + AllNumArray[Index1] + ", and its index is " + Index1);
    System.out.println("The second Nnumber is " + AllNumArray[Index2] + ", and its index is " + Index2);
}

}

Answer 1

你可以得到如下的最后一个对象：

ArrayList<Integer> AllNum = new ArrayList<>();
        do
        {
            System.out.println ("Please enter a num");
            AllNum.add (sc.nextInt());
            System.out.println ("Do you want to enter a new sentence? Enter Y for yes and N for no");
            x = sc.nextLine();
        } while ("Y".equals(x));
        int Index = AllNum.get(AllNum.size() - 1); // change is here
        int [] AllNumArray = new int [Index];

x list x的{{1}}索引为string Y，因此它不在列表中，因此returns -1。查看JavaDoc

public int lastIndexOf（@ org.jetbrains.annotations.Nullable java.lang.Object o）返回此列表中指定元素最后一次出现的索引，如果此列表不包含该元素，则返回-1。更正式地，返回最高索引i，使得（o == null？get（i）== null：o.equals（get（i））），或-1，如果没有这样的索引。 的

编辑：重写代码：

Scanner sc = new Scanner(System.in); String x; // no need to init here String x = ""; int Distance = 0; int Index1 = 0; int Index2 = 0; List<Integer> AllNum = new ArrayList<>(); do { System.out.println("Please enter a number"); int NewNumber = sc.nextInt(); AllNum.add(NewNumber); System.out.println("Do you want to enter a new number? Enter Y for yes and N for no"); x = sc.next(); // here changed sc.nextLine() -> sc.next() } while (x.equalsIgnoreCase("y")); // here changed equals() -> equalsIgnoreCase() int Index = AllNum.size(); int[] AllNumArray = new int[Index]; for (int i = 0; i < Index; i++) { AllNumArray[i] = AllNum.get(i); } for (int i = 0; i < Index; i++) { // here changed, and the main problem was here, int nextIndex = i < AllNumArray.length - 1 ? i + 1 : 0; int NewDistance = AllNumArray[i] - AllNumArray[nextIndex]; if (NewDistance > Distance) { Distance = NewDistance; Index1 = i; Index2 = i + 1; } } System.out.println("The smallest distance between two neighboring numbers is: " + Distance); System.out.println("The first Nnumber is " + AllNumArray[Index1] + ", and its index is " + Index1); System.out.println("The second Nnumber is " + AllNumArray[Index2] + ", and its index is " + Index2);

当我尝试创建一个数组时，它会给我一个错误＆＃34;这个数组只能从＆＃34;中读取，为什么我不能在其中写入？

1 个答案: