Question

运行程序后，它指示我If (key.compareTo(a[mid]) == 0)它出了什么问题？

线程“main”中的异常java.lang.ArrayIndexOutOfBoundsException：5 在BinarySearch.search（BinarySearch.java:17）at SearchesDemo.main（SearchesDemo.java:23）

import java.util.Scanner;
import java.util.Arrays;

public class SearchesDemo{

  public static void main(String[] args){
    BinarySearch searches = new BinarySearch();
    int result, key;
    Integer [] integerArray = {0, 2, 4, 6, 8, 10, 12, 14, 16, 18};
    String [] stringArray = {"apples", "oranges", "peaches", "strawberries", "watermelons"};

    System.out.println("Integer test array contains:");
    System.out.println(Arrays.toString(integerArray));

    for(key = -3; key == 4; key++){
      result = searches.<Integer>search(integerArray, 0, 10, key);
      searches.toString(Integer.toString(key), result);
    }

    System.out.println("\nString test array contains:");
    System.out.println(Arrays.toString(stringArray)); //toString may not be necessary

    result = searches.<String>search(stringArray, 0, 10, "apples");
    searches.toString("apples", result);
    result = searches.<String>search(stringArray, 0, 10, "plums");
    searches.toString("plums", result);

    System.out.println("\nProcess completed.");
  }
}

public class BinarySearch{


  public static <T extends Comparable> int search(T [] a, int first, int last, T key){
    int result = 0; //to keep the compiler happy.

    if (first > last)
      result = -1;
    else{
      int mid = (first + last)/2;

      if (key.compareTo(a[mid]) == 0)
        result = mid;
      else if (key.compareTo(a[mid]) < 0)
        result = search(a, first, mid - 1, key);
      else if (key.compareTo(a[mid]) > 0)
        result = search(a, mid + 1, last, key);
      else{
        System.out.println("Error");
        result = -1;
      }
    }
    return result;
  }

  public static void toString(String key, int result){
    if(result == -1)
      System.out.println(key + " is not in the array.");
    else
      System.out.println(key + " is at index " + result);
  }
}

Answer 1

请勿为10值发送last。只需发送数组的长度。

result = searches.<String>search(stringArray, 0, stringArray.length, "apples");
searches.toString("apples", result);
result = searches.<String>search(stringArray, 0, stringArray.length, "plums");
searches.toString("plums", result);

同样在这里：

result = searches.<Integer>search(integerArray, 0, integerArray.length, key);

Answer 2

问题是你的stringArray中有5个元素（索引0,1,2,3,4），并且因为你从开始索引为0开始，最后是10，因此介质是5，因此你试图访问不存在的索引 - ＆gt;出界。

Answer 3

主方法中的行号 23 发生异常。您将开始和结束索引传递为0和10。

 result = searches.<String>search(stringArray, 0, 10, "apples");

stringarray的长度仅为5.当计算中间值时，它变为(0+10)/2，即5. arr[5]抛出arrayIndexOutOfBound例外。

线程“main”中的异常java.lang.ArrayIndexOutOfBoundsException：5

3 个答案: