Operations on arrays, primitive arrays (like int[]) and primitive wrapper arrays (like Integer[]).

This class tries to handle null input gracefully. 

Operations on bit-mapped fields.

Operations on boolean primitives and Boolean objects.

This class tries to handle null input gracefully. 

Character encoding names required of every implementation of the Java platform. 

A contiguous range of characters, optionally negated.

Instances are immutable.

A set of characters.

Instances are immutable, but instances of subclasses may not be.

Operations on CharSets.

This class handles null input gracefully. 

Operations on char primitives and Character objects.

This class tries to handle null input gracefully. 

Operates on classes without using reflection.

This class handles invalid null inputs as best it can. 

Provides HTML and XML entity utilities. 

Thrown when an object is an instance of an unexpected type (a class or interface). 

Thrown to indicate an incomplete argument to a method. 

A hash map that uses primitive ints for the key rather than objects.

Note that this class is for internal optimization purposes only, and may not be supported in future releases of Apache Commons Lang. 

Innerclass that acts as a datastructure to create a new entry in the table.

Operations to assist when working with a Locale .

This class tries to handle null input gracefully. 

Thrown to indicate that a block of code has not been implemented. 

Thrown to indicate that an argument was null and should not have been. 

Represents a range of Number objects.

This class uses double comparisons. 

Provides extra functionality for Java Number classes.

Operations on Object.

This class tries to handle null input gracefully. 

Class used as a null placeholder where null has another meaning.

For example, in a HashMap the java.util.HashMap#get(java.lang.Object) method returns null if the Map contains null or if there is no matching key. 

Operations for random Strings.

Currently private high surrogate characters are ignored. 

Exception thrown when the Serialization process fails.

The original error is wrapped within this one.

Assists with the serialization process and performs additional functionality based on serialization.

• Deep clone using serialization
• Serialize managing finally and IOException
• Deserialize managing finally and IOException

This class throws exceptions for invalid null inputs. 

Escapes and unescapes Strings for Java, Java Script, HTML, XML, and SQL.

A PrintWriter that maintains a String as its backing store.

Usage:

StringPrintWriter out = new StringPrintWriter();
printTo(out);
System.out.println( out.getString() );

Operations on java.lang.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
• LevensteinDistance - the number of changes needed to change one String into another

The StringUtils class defines certain words related to String handling.

• null - null
• empty - a zero-length string ("")
• space - the space character (' ', char 32)
• whitespace - the characters defined by Character#isWhitespace(char)
• trim - the characters <= 32 as in String#trim()

StringUtils handles null input Strings quietly. 

Helpers for java.lang.System.

If a system property cannot be read due to security restrictions, the corresponding field in this class will be set to null and a message will be written to System.err.

Thrown when it is impossible or undesirable to consume or throw a checked exception.

UnhandledException represents the case where a method has to deal with a checked exception but does not wish to. 

Assists in validating arguments.

The class is based along the lines of JUnit. 

Operations on Strings that contain words.

This class tries to handle null input gracefully.