Reading Characters from String Builders

The following methods can be used for reading characters in a string builder:

char charAt(int index)
From the
CharSequence
interface (p. 444)
.
void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin)

Copies characters from the current string builder into the destination character array. Characters from the current string builder are read from index srcBegin to index srcEnd-1, inclusive. They are copied into the destination array (dst), starting at index dstBegin and ending at index dstbegin+(srcEnd-srcBegin)-1. The number of characters copied is (srcEnd-srcBegin). An IndexOutOfBoundsException is thrown if the indices do not meet the criteria for the operation.

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IntStream chars()
From the
CharSequence
interface (p. 444).
int length()
From the
CharSequence
interface (p. 444).

The following is an example of reading the contents of a string builder:

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StringBuilder strBuilder = new StringBuilder(“Java”); // “Java”, capacity 20
char charFirst = strBuilder.charAt(0); // ‘J’
char charLast = strBuilder.charAt(strBuilder.length()-1); // ‘a’

Searching for Substrings in String Builders

The methods for searching substrings in string builders are analogous to the ones in the String class (p. 451).

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int indexOf(String substr)
int indexOf(String substr, int fromIndex)

int lastIndexOf(String str)
int lastIndexOf(String str, int fromIndex)

Examples of searching for substrings in a StringBuilder:

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StringBuilder banner2 = new StringBuilder(“One man, One vote”);
//                                         01234567890123456
int subInd1a = banner2.indexOf(“One”);         // 0
int subInd1b = banner2.indexOf(“One”, 3);      // 9
int subInd2a = banner2.lastIndexOf(“One”);     // 9
int subInd2b = banner2.lastIndexOf(“One”, 10); // 9
int subInd2c = banner2.lastIndexOf(“One”, 8); // 0
int subInd2d = banner2.lastIndexOf(“One”, 2); // 0

Extracting Substrings from String Builders

The StringBuilder class provides the following methods to extract substrings, which are also provided by the String class (p. 453).

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String substring(int startIndex)
String substring(int startIndex, int endIndex)

CharSequence subSequence(int start, int end)
From the
CharSequence
interface
(
p. 444
).

Examples of extracting substrings:

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StringBuilder bookName = new StringBuilder(“Java Gems by Anonymous”);
//                                          01234567890123456789012
String title = bookName.substring(0,9);   // “Java Gems”
String author = bookName.substring(13);    // “Anonymous”