1. String str="ddd";
   
2. String ss=str.substring(3);
   
3. System.out.println(ss);

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大家帮我看看字符串角标为什么没有出越界异常

String类源码实现

1. /**
   
2.      * Returns a string that is a substring of this string. The
   
3.      * substring begins with the character at the specified index and
   
4.      * extends to the end of this string. <p>
   
5.      * Examples:
   
6.      * <blockquote><pre>
   
7.      * "unhappy".substring(2) returns "happy"
   
8.      * "Harbison".substring(3) returns "bison"
   
9.      * "emptiness".substring(9) returns "" (an empty string)
   
10.      * </pre></blockquote>
    
11.      *
    
12.      * @param      beginIndex   the beginning index, inclusive.
    
13.      * @return     the specified substring.
    
14.      * @exception  IndexOutOfBoundsException  if
    
15.      *             {@code beginIndex} is negative or larger than the
    
16.      *             length of this {@code String} object.
    
17.      */
    
18.     public String substring(int beginIndex) {
    
19.         if (beginIndex < 0) {
    
20.             throw new StringIndexOutOfBoundsException(beginIndex);
    
21.         }
    
22.         int subLen = value.length - beginIndex;
    
23.         if (subLen < 0) {
    
24.             throw new StringIndexOutOfBoundsException(subLen);
    
25.         }
    
26.         return (beginIndex == 0) ? this : new String(value, beginIndex, subLen);
    
27.     }

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不知道你有没有听说过这样一句话：字符串的截取是包括头不包括尾的

ddd是 0 1 2没有3  更没有3以后的  。。。。subString (int index)是从index开始到length 你3已然越界了 少年

在基础班还没上到这