The Java API Documentation is the core reference that we have in the Java programming language and it is vital that you understand how to navigate, comprehend and apply the documentation to your code.

Figure 4.5, “The Java API Documentation” shows a screen grab of the API documentation in use. It consists of three frames:

Figure 4.5. The Java API Documentation

You should download and install the Java API documentation for this module as discussed in the section called “The Java 2 Software Development Kit (Java SDK)”.

Below, you will find the API documentation for the String, showing a description of the class and the constructors and methods available. This piece of text is much easier to read in the API documentaton (String).

 java.lang 
 Class String

 java.lang.Object
   |
   +--java.lang.String
  
 All Implemented Interfaces: 
 CharSequence, Comparable, Serializable 

--------------------------------------------------------------------------------

 public final class String
 extends Object
 implements Serializable, Comparable, CharSequence

 The String class represents character strings. All string literals in Java 
 programs, such as "abc", are implemented as instances of this class. 

 Strings are constant; their values cannot be changed after they are created. 
 String buffers support mutable strings. Because String objects are immutable 
 they can be shared. For example: 

     String str = "abc";
     
 is equivalent to: 

     char data[] = {'a', 'b', 'c'};
     String str = new String(data);
     
 Here are some more examples of how strings can be used: 

     System.out.println("abc");
     String cde = "cde";
     System.out.println("abc" + cde);
     String c = "abc".substring(2,3);
     String d = cde.substring(1, 2);
     
 The class String includes methods for examining individual characters of the 
 sequence, for comparing strings, for searching strings, for extracting 
 substrings, and for creating a copy of a string with all characters translated 
 to uppercase or to lowercase. Case mapping relies heavily on the information 
 provided by the Unicode Consortium's Unicode 3.0 specification. The 
 specification's UnicodeData.txt and SpecialCasing.txt files are used 
 extensively to provide case mapping. 

 The Java language provides special support for the string concatenation 
 operator ( + ), and for conversion of other objects to strings. String 
 concatenation is implemented through the StringBuffer class and its 
 append method. String conversions are implemented through the method toString, 
 defined by Object and inherited by all classes in Java. For additional 
 information on string concatenation and conversion, see Gosling, Joy, and 
 Steele, The Java Language Specification. 


 Since: 
 JDK1.0 
 
 See Also:
 Object.toString(), StringBuffer, StringBuffer.append(boolean), 
 StringBuffer.append(char), StringBuffer.append(char[]), StringBuffer.append(char[], 
 int, int), StringBuffer.append(double), StringBuffer.append(float), 
 StringBuffer.append(int), StringBuffer.append(long), StringBuffer.append(java.lang.Object),
 StringBuffer.append(java.lang.String), Charset, Serialized Form

Constructor Summary
String() 
          Initializes a newly created String object so that it represents 
          an empty character sequence. 
String(byte[] bytes) 
          Constructs a new String by decoding the specified array of bytes 
          using the platform's default charset. 
String(byte[] ascii, int hibyte) 
          Deprecated. This method does not properly convert bytes into 
          characters. As of JDK 1.1, the preferred way to do this is via 
          the String constructors that take a charset name or that use the 
          platform's default charset. 
String(byte[] bytes, int offset, int length) 
          Constructs a new String by decoding the specified subarray of bytes 
          using the platform's default charset. 
String(byte[] ascii, int hibyte, int offset, int count) 
          Deprecated. This method does not properly convert bytes into 
          characters. As of JDK 1.1, the preferred way to do this is via 
          the String constructors that take a charset name or that use the 
          platform's default charset. 
String(byte[] bytes, int offset, int length, String charsetName) 
          Constructs a new String by decoding the specified subarray of bytes 
          using the specified charset. 
String(byte[] bytes, String charsetName) 
          Constructs a new String by decoding the specified array of bytes 
          using the specified charset. 
String(char[] value) 
          Allocates a new String so that it represents the sequence of 
          characters currently contained in the character array argument. 
String(char[] value, int offset, int count) 
          Allocates a new String that contains characters from a subarray 
          of the character array argument. 
String(String original) 
          Initializes a newly created String object so that it represents 
          the same sequence of characters as the argument; in other words, 
          the newly created string is a copy of the argument string. 
String(StringBuffer buffer) 
          Allocates a new string that contains the sequence of characters 
          currently contained in the string buffer argument. 


Method Summary
 char charAt(int index)
          Returns the character at the specified index. 
 int compareTo(Object o) 
          Compares this String to another Object. 
 int compareTo(String anotherString) 
          Compares two strings lexicographically. 
 int compareToIgnoreCase(String str) 
          Compares two strings lexicographically, ignoring case differences. 
 String concat(String str) 
          Concatenates the specified string to the end of this string. 
 boolean contentEquals(StringBuffer sb) 
          Returns true if and only if this String represents the same sequence 
          of characters as the specified StringBuffer. 
 static String copyValueOf(char[] data) 
          Returns a String that represents the character sequence in the 
          array specified. 
 static String copyValueOf(char[] data, int offset, int count) 
          Returns a String that represents the character sequence in the 
          array specified. 
 boolean endsWith(String suffix) 
          Tests if this string ends with the specified suffix. 
 boolean equals(Object anObject) 
          Compares this string to the specified object. 
 boolean equalsIgnoreCase(String anotherString) 
          Compares this String to another String, ignoring case 
          considerations. 
 byte[] getBytes() 
          Encodes this String into a sequence of bytes using the platform's 
          default charset, storing the result into a new byte array. 
 void getBytes(int srcBegin, int srcEnd, byte[] dst, int dstBegin)
          Deprecated. This method does not properly convert characters into 
          bytes. As of JDK 1.1, the preferred way to do this is via the 
          the getBytes() method, which uses the platform's default charset. 
 byte[] getBytes(String charsetName) 
          Encodes this String into a sequence of bytes using the named
           charset, storing the result into a new byte array. 
 void getChars(int srcBegin, int srcEnd, char[] dst, int dstBegin) 
          Copies characters from this string into the destination character 
          array. 
 int hashCode() 
          Returns a hash code for this string. 
 int indexOf(int ch) 
          Returns the index within this string of the first occurrence of 
          the specified character. 
 int indexOf(int ch, int fromIndex) 
          Returns the index within this string of the first occurrence of 
          the specified character, starting the search at the specified 
          index. 
 int indexOf(String str) 
          Returns the index within this string of the first occurrence of 
          the specified substring. 
 int indexOf(String str, int fromIndex) 
          Returns the index within this string of the first occurrence of 
          the specified substring, starting at the specified index. 
 String intern() 
          Returns a canonical representation for the string object. 
 int lastIndexOf(int ch) 
          Returns the index within this string of the last occurrence 
          of the specified character. 
 int lastIndexOf(int ch, int fromIndex) 
          Returns the index within this string of the last occurrence of 
          the specified character, searching backward starting at the
           specified index. 
 int lastIndexOf(String str) 
          Returns the index within this string of the rightmost occurrence 
          of the specified substring. 
 int lastIndexOf(String str, int fromIndex) 
          Returns the index within this string of the last occurrence of 
          the specified substring, searching backward starting at the 
          specified index. 
 int length() 
          Returns the length of this string. 
 boolean matches(String regex) 
          Tells whether or not this string matches the given regular expression. 
 boolean regionMatches(boolean ignoreCase, int toffset, 
 			String other, int ooffset, int len) 
          Tests if two string regions are equal. 
 boolean regionMatches(int toffset, String other, int ooffset, int len) 
          Tests if two string regions are equal. 
 String replace(char oldChar, char newChar) 
          Returns a new string resulting from replacing all occurrences of 
          oldChar in this string with newChar. 
 String replaceAll(String regex, String replacement) 
          Replaces each substring of this string that matches the given 
          regular expression with the given replacement. 
 String replaceFirst(String regex, String replacement) 
          Replaces the first substring of this string that matches the 
          given regular expression with the given replacement. 
 String[] split(String regex) 
          Splits this string around matches of the given regular expression. 
 String[] split(String regex, int limit) 
          Splits this string around matches of the given regular expression. 
 boolean startsWith(String prefix) 
          Tests if this string starts with the specified prefix. 
 boolean startsWith(String prefix, int toffset) 
          Tests if this string starts with the specified prefix beginning a 
          specified index. 
 CharSequence subSequence(int beginIndex, int endIndex) 
          Returns a new character sequence that is a subsequence of this 
          sequence. 
 String substring(int beginIndex) 
          Returns a new string that is a substring of this string. 
 String substring(int beginIndex, int endIndex) 
          Returns a new string that is a substring of this string. 
 char[] toCharArray() 
          Converts this string to a new character array. 
 String toLowerCase() 
          Converts all of the characters in this String to lower case 
          using the rules of the default locale. 
 String toLowerCase(Locale locale) 
          Converts all of the characters in this String to lower case 
          using the rules of the given Locale. 
 String toString() 
          This object (which is already a string!) is itself returned. 
 String toUpperCase() 
          Converts all of the characters in this String to upper case 
          using the rules of the default locale. 
 String toUpperCase(Locale locale) 
          Converts all of the characters in this String to upper case 
          using the rules of the given Locale. 
 String trim() 
          Returns a copy of the string, with leading and trailing 
          whitespace omitted. 
 static String valueOf(boolean b) 
          Returns the string representation of the boolean argument. 
 static String valueOf(char c) 
          Returns the string representation of the char argument. 
 static String valueOf(char[] data) 
          Returns the string representation of the char array argument. 
 static String valueOf(char[] data, int offset, int count) 
          Returns the string representation of a specific subarray of 
          the char array argument. 
 static String valueOf(double d) 
          Returns the string representation of the double argument. 
 static String valueOf(float f) 
          Returns the string representation of the float argument. 
 static String valueOf(int i) 
          Returns the string representation of the int argument. 
 static String valueOf(long l) 
          Returns the string representation of the long argument. 
 static String valueOf(Object obj) 
          Returns the string representation of the Object argument.