为什么我的程序抛出StringIndexOutOfBounds异常？

Question

我正在编写一个程序来计算:

1 ^ 1 + 2 ^ 2 + 3 ^ 3 + ... + 1000 ^ 1000 =？

一旦计算完毕,我想删除除最后十位数之外的答案中的所有数字,然后在屏幕上打印最后十位数字.但是,要删除我使用该StringBuilder.deleteCharAt()方法的所有其他数字,这会导致一些问题.我在下面提供了我的代码:

import java.math.BigInteger;
public class problemFourtyEight {
  public static void main(String [] args) {
    BigInteger answer = new BigInteger(""+0);
    for(int i = 0; i <= 1000; i++) {
      BigInteger temp = new BigInteger(""+i);
      temp = temp.pow(i);
      answer = answer.add(temp);
    }
    System.out.println(answer.toString().length());
    StringBuilder sb = new StringBuilder((answer.toString()));
    for(int k = 0; k <= (answer.toString().length() - 10); k++) {
      sb.deleteCharAt(k);  //Line 13 is here.
    }
    String finalAnswer = sb.toString();
    System.out.println(finalAnswer);
  }
}

抛出的异常是:

Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: 1501
    at java.lang.AbstractStringBuilder.deleteCharAt(AbstractStringBuilder.java:797)
    at java.lang.StringBuilder.deleteCharAt(StringBuilder.java:253)
    at problemFourtyEight.main(problemFourtyEight.java:13)

从打印出答案的长度(删除任何字符之前),它告诉我数字的长度是3001,所以我不明白为什么String index1,501被称为OutOfBounds.

Answer 1

你的错误是这段代码:

StringBuilder sb = new StringBuilder((answer.toString()));
for(int k = 0; k <= (answer.toString().length() - 10); k++) {
  sb.deleteCharAt(k);  //Line 13 is here.
}

由于字符串构建器的可变性,使字符串变得更短.你要:

System.out.println(answer.substring(answer.length()-10))

如果这对您很重要,这也具有速度的优势.