JDK6和JDK7中String类下的substring方法的代码对比（仅贴代码，未详述）

 1 /**
 2      * Returns a new 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</code> is negative or larger than the
16      *             length of this <code>String</code> object.
17      */
18     public String substring(int beginIndex) {
19     return substring(beginIndex, count);
20     }
21 
22     /**
23      * Returns a new string that is a substring of this string. The
24      * substring begins at the specified <code>beginIndex</code> and
25      * extends to the character at index <code>endIndex - 1</code>.
26      * Thus the length of the substring is <code>endIndex-beginIndex</code>.
27      * <p>
28      * Examples:
29      * <blockquote><pre>
30      * "hamburger".substring(4, 8) returns "urge"
31      * "smiles".substring(1, 5) returns "mile"
32      * </pre></blockquote>
33      *
34      * @param      beginIndex   the beginning index, inclusive.
35      * @param      endIndex     the ending index, exclusive.
36      * @return     the specified substring.
37      * @exception  IndexOutOfBoundsException  if the
38      *             <code>beginIndex</code> is negative, or
39      *             <code>endIndex</code> is larger than the length of
40      *             this <code>String</code> object, or
41      *             <code>beginIndex</code> is larger than
42      *             <code>endIndex</code>.
43      */
44     public String substring(int beginIndex, int endIndex) {
45     if (beginIndex < 0) {
46         throw new StringIndexOutOfBoundsException(beginIndex);
47     }
48     if (endIndex > count) {
49         throw new StringIndexOutOfBoundsException(endIndex);
50     }
51     if (beginIndex > endIndex) {
52         throw new StringIndexOutOfBoundsException(endIndex - beginIndex);
53     }
54     return ((beginIndex == 0) && (endIndex == count)) ? this :
55         new String(offset + beginIndex, endIndex - beginIndex, value);
56     }

 1 /**
 2      * Returns a new 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</code> is negative or larger than the
16      *             length of this <code>String</code> 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     }
28 
29     /**
30      * Returns a new string that is a substring of this string. The
31      * substring begins at the specified <code>beginIndex</code> and
32      * extends to the character at index <code>endIndex - 1</code>.
33      * Thus the length of the substring is <code>endIndex-beginIndex</code>.
34      * <p>
35      * Examples:
36      * <blockquote><pre>
37      * "hamburger".substring(4, 8) returns "urge"
38      * "smiles".substring(1, 5) returns "mile"
39      * </pre></blockquote>
40      *
41      * @param      beginIndex   the beginning index, inclusive.
42      * @param      endIndex     the ending index, exclusive.
43      * @return     the specified substring.
44      * @exception  IndexOutOfBoundsException  if the
45      *             <code>beginIndex</code> is negative, or
46      *             <code>endIndex</code> is larger than the length of
47      *             this <code>String</code> object, or
48      *             <code>beginIndex</code> is larger than
49      *             <code>endIndex</code>.
50      */
51     public String substring(int beginIndex, int endIndex) {
52         if (beginIndex < 0) {
53             throw new StringIndexOutOfBoundsException(beginIndex);
54         }
55         if (endIndex > value.length) {
56             throw new StringIndexOutOfBoundsException(endIndex);
57         }
58         int subLen = endIndex - beginIndex;
59         if (subLen < 0) {
60             throw new StringIndexOutOfBoundsException(subLen);
61         }
62         return ((beginIndex == 0) && (endIndex == value.length)) ? this
63                 : new String(value, beginIndex, subLen);
64     }