StringUtils阅读笔记

总结：

1，在JDK的开头。关于这个类的大致有哪些功能已经相当的清楚了。

ations on String that are null safe.

• IsEmpty/IsBlank - checks if a String contains text
• Trim/Strip - removes leading and trailing whitespace
• Equals - compares two strings null-safe
• startsWith - check if a String starts with a prefix null-safe
• endsWith - check if a String ends with a suffix null-safe
• IndexOf/LastIndexOf/Contains - null-safe index-of checks
• IndexOfAny/LastIndexOfAny/IndexOfAnyBut/LastIndexOfAnyBut - index-of any of a set of Strings
• ContainsOnly/ContainsNone/ContainsAny - does String contains only/none/any of these characters
• Substring/Left/Right/Mid - null-safe substring extractions
• SubstringBefore/SubstringAfter/SubstringBetween - substring extraction relative to other strings
• Split/Join - splits a String into an array of substrings and vice versa
• Remove/Delete - removes part of a String
• Replace/Overlay - Searches a String and replaces one String with another
• Chomp/Chop - removes the last part of a String
• LeftPad/RightPad/Center/Repeat - pads a String
• UpperCase/LowerCase/SwapCase/Capitalize/Uncapitalize - changes the case of a String
• CountMatches - counts the number of occurrences of one String in another
• IsAlpha/IsNumeric/IsWhitespace/IsAsciiPrintable - checks the characters in a String
• DefaultString - protects against a null input String
• Reverse/ReverseDelimited - reverses a String
• Abbreviate - abbreviates a string using ellipsis
• Difference - compares Strings and reports on their differences
• LevenshteinDistance - the number of changes needed to change one String into another

2 这两组的区别，主要是后一组，是一个数组。

IndexOf/LastIndexOf/Contains - null-safe index-of checks

IndexOfAny/LastIndexOfAny/IndexOfAnyBut/LastIndexOfAnyBut - index-of any of a set of Strings

 

3  Replace/Overlay - Searches a String and replaces one String with another

Replace主要是从字符串角度。比如说abcde当中，替换掉c。

Overlay主要从长度的角度，比如说abcdef中，替换掉从第二位，到第三位。

 

4， DefaultString - protects against a null input String， 可以用来null处理。

 

5,  Difference , 是以前面一个为基准进行比较。具体可以看API，然后str2的第二个字段开始截取。由于Str2使用了String方法的subString方法。所以注意可能有内存泄露的问题。

StringUtils.difference("abcde", "abxyz") = "xyz"

StringUtils.difference("abcde", "xyz") = "xyz"

 

6，看了一下，其内部的实现。字符串的循环其中的character。并对其进行判断。然后用StringBuilder来进行组装，也就是说，其不保持多线程安全。（其实这个说法不准确。因为其实方法的变量。所以call这个方法，是安全，外面安不安全。就是看你自己了）

 

7,看到了源代码中，这么一段注释。

// Performance testing notes (JDK 1.4, Jul03, scolebourne)
// Whitespace:
// Character.isWhitespace() is faster than WHITESPACE.indexOf()
// where WHITESPACE is a string of all whitespace characters
//
// Character access:
// String.charAt(n) versus toCharArray(), then array[n]
// String.charAt(n) is about 15% worse for a 10K string
/ They are about equal for a length 50 string
// String.charAt(n) is about 4 times better for a length 3 string
// String.charAt(n) is best bet overall
//
// Append:
// String.concat about twice as fast as StringBuffer.append
// (not sure who tested this)