Question

以下程序出现异常：

Exception in thread "main" java.lang.StringIndexOutOfBoundsException: String index out of range: -2
    at java.lang.String.substring(String.java:1911)
    at Names.main(Names.java:33)

换行

System.out.println("The character at index 3 in "+middle+" is "+middle.substring(3, 1));

你觉得这行有什么问题吗？

/* Names.java */

import java.io.*;

public class Names {

/** Performs various string operations on the name John Fitzgerald kennedy.
 *     
 * @param arg is not used
 */

    public static void main(String[] args) {
        String first = "john";
        String middle = "Fitzgerald";
        String last = "Kennedy";
        String initials;
        String firstInit, middleInit, lastInit;

        firstInit = first.substring(0, 1);
        middleInit = middle.substring(0,1);
        lastInit = last.substring(0,1);
        initials = firstInit.concat(middleInit);
        initials = initials.concat(lastInit);

        System.out.println();
        System.out.println(first+" "+middle+" "+last+" ");
        System.out.println(initials);
        System.out.println(last+", "+first+" "+middle);
        System.out.println(last+", "+first+" "+middleInit+".");
        System.out.println(first.toUpperCase()+" "+last.toUpperCase());

        System.out.println(first+" equals john is "+first.equals("john"));
        System.out.println(first+" equals john (ignoring case is) "+first.equalsIgnoreCase("john"));
        System.out.println("The character at index 3 in "+middle+" is "+middle.substring(3, 1));
        System.out.println("The index of \"gerald\" within "+middle+" is "+middle.indexOf("gerald"));
        System.out.println("The index of \"gerald\" within "+last+" is "+last.indexOf("gerald"));

        System.out.println();
    }

}

Answer 1

这不起作用：

middle.substring(3, 1)

您的结束值不能大于String#substring()的起始值：

引发IndexOutOfBoundsException - 如果beginIndex为否定，或endIndex大于此String对象的长度，或 beginIndex大于{{ 1}}

由于您只想要索引3处的字符，请改为使用endIndex：

charAt()

或者，使用范围较窄的middle.charAt(3);：

substring

Answer 2

您必须将（开始，结束）参数传递给substring：

middle.substring(3, 4) // '4' since you just want one char

请记住，substring()不会返回索引4的字符。

注意：更简单的方法是使用charAt(index)：

middle.charAt(3)

Answer 3

方法签名是

public String substring(int beginIndex, int endIndex)

因此，如果你想打一个角色，你应该使用

middle.substring(3, 4);

Answer 4

middle.substring(from index , to index)在使用子字符串middle.substring(3, 1)

时，您在此处做了什么to index greater than from index

研究Java中的字符串操作

Answer 5

从o this documentation开始，很明显，如果beginIndex为负数，或者endIndex大于此String对象的长度，或者beginIndex大于endIndex，则subString（）方法将抛出IndexOutOfBoundsException。

字符串索引超出范围：-2

5 个答案: