5.4 - The Java API Documentation

The Java API Documentation

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

  • The top left frame displays the packages in the API.

  • The bottom left frame displays the classes and interfaces in the package chosen, or if no package is chosen, all classes and interfaces are displayed.

  • The right hand frame displays the documentation on the class or interface chosen in the bottom left hand side.

Figure 5.5. The Java API Documentation


You should download and install the Java API documentation for this module as previously discussed.

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 documentation (String).

java.lang

Class String

  • All Implemented Interfaces:
    SerializableCharSequenceComparable<String>


    public final class String
    extends Object
    implements Serializable, Comparable<String>, 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 is based on the Unicode Standard version specified by the Character class.

    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 StringBuilder(orStringBuffer) 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.

    Unless otherwise noted, passing a null argument to a constructor or method in this class will cause a NullPointerException to be thrown.

    String represents a string in the UTF-16 format in which supplementary characters are represented by surrogate pairs (see the section Unicode Character Representations in the Character class for more information). Index values refer to char code units, so a supplementary character uses two positions in a String.

    The String class provides methods for dealing with Unicode code points (i.e., characters), in addition to those for dealing with Unicode code units (i.e., char values).

    Since:
    JDK1.0
    See Also:
    Object.toString()StringBufferStringBuilderCharsetSerialized Form
    • Constructor Summary

      Constructors 
      Constructor and Description
      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[] bytes, Charset charset)
      Constructs a new String by decoding the specified array of bytes using the specified 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, 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[] bytes, int offset, int length, Charset charset)
      Constructs a new String by decoding the specified subarray of bytes using the specified 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, 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(int[] codePoints, int offset, int count)
      Allocates a new String that contains characters from a subarray of the Unicode code point 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.
      String(StringBuilder builder)
      Allocates a new string that contains the sequence of characters currently contained in the string builder argument.
    • Method Summary

      Methods 
      Modifier and TypeMethod and Description
      charcharAt(int index)
      Returns the char value at the specified index.
      intcodePointAt(int index)
      Returns the character (Unicode code point) at the specified index.
      intcodePointBefore(int index)
      Returns the character (Unicode code point) before the specified index.
      intcodePointCount(int beginIndex, int endIndex)
      Returns the number of Unicode code points in the specified text range of this String.
      intcompareTo(String anotherString)
      Compares two strings lexicographically.
      intcompareToIgnoreCase(String str)
      Compares two strings lexicographically, ignoring case differences.
      Stringconcat(String str)
      Concatenates the specified string to the end of this string.
      booleancontains(CharSequence s)
      Returns true if and only if this string contains the specified sequence of char values.
      booleancontentEquals(CharSequence cs)
      Compares this string to the specified CharSequence.
      booleancontentEquals(StringBuffer sb)
      Compares this string to the specified StringBuffer.
      static StringcopyValueOf(char[] data)
      Returns a String that represents the character sequence in the array specified.
      static StringcopyValueOf(char[] data, int offset, int count)
      Returns a String that represents the character sequence in the array specified.
      booleanendsWith(String suffix)
      Tests if this string ends with the specified suffix.
      booleanequals(Object anObject)
      Compares this string to the specified object.
      booleanequalsIgnoreCase(String anotherString)
      Compares this String to another String, ignoring case considerations.
      static Stringformat(Locale l, String format, Object... args)
      Returns a formatted string using the specified locale, format string, and arguments.
      static Stringformat(String format, Object... args)
      Returns a formatted string using the specified format string and arguments.
      byte[]getBytes()
      Encodes this String into a sequence of bytes using the platform's default charset, storing the result into a new byte array.
      byte[]getBytes(Charset charset)
      Encodes this String into a sequence of bytes using the given charset, storing the result into a new byte array.
      voidgetBytes(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 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.
      voidgetChars(int srcBegin, int srcEnd, char[] dst, int dstBegin)
      Copies characters from this string into the destination character array.
      inthashCode()
      Returns a hash code for this string.
      intindexOf(int ch)
      Returns the index within this string of the first occurrence of the specified character.
      intindexOf(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.
      intindexOf(String str)
      Returns the index within this string of the first occurrence of the specified substring.
      intindexOf(String str, int fromIndex)
      Returns the index within this string of the first occurrence of the specified substring, starting at the specified index.
      Stringintern()
      Returns a canonical representation for the string object.
      booleanisEmpty()
      Returns true if, and only if, length() is 0.
      intlastIndexOf(int ch)
      Returns the index within this string of the last occurrence of the specified character.
      intlastIndexOf(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.
      intlastIndexOf(String str)
      Returns the index within this string of the last occurrence of the specified substring.
      intlastIndexOf(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.
      intlength()
      Returns the length of this string.
      booleanmatches(String regex)
      Tells whether or not this string matches the given regular expression.
      intoffsetByCodePoints(int index, int codePointOffset)
      Returns the index within this String that is offset from the given index by codePointOffset code points.
      booleanregionMatches(boolean ignoreCase, int toffset, String other, int ooffset, int len)
      Tests if two string regions are equal.
      booleanregionMatches(int toffset, String other, int ooffset, int len)
      Tests if two string regions are equal.
      Stringreplace(char oldChar, char newChar)
      Returns a new string resulting from replacing all occurrences of oldChar in this string with newChar.
      Stringreplace(CharSequence target, CharSequence replacement)
      Replaces each substring of this string that matches the literal target sequence with the specified literal replacement sequence.
      StringreplaceAll(String regex, String replacement)
      Replaces each substring of this string that matches the given regular expression with the given replacement.
      StringreplaceFirst(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.
      booleanstartsWith(String prefix)
      Tests if this string starts with the specified prefix.
      booleanstartsWith(String prefix, int toffset)
      Tests if the substring of this string beginning at the specified index starts with the specified prefix.
      CharSequencesubSequence(int beginIndex, int endIndex)
      Returns a new character sequence that is a subsequence of this sequence.
      Stringsubstring(int beginIndex)
      Returns a new string that is a substring of this string.
      Stringsubstring(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.
      StringtoLowerCase()
      Converts all of the characters in this String to lower case using the rules of the default locale.
      StringtoLowerCase(Locale locale)
      Converts all of the characters in this String to lower case using the rules of the given Locale.
      StringtoString()
      This object (which is already a string!) is itself returned.
      StringtoUpperCase()
      Converts all of the characters in this String to upper case using the rules of the default locale.
      StringtoUpperCase(Locale locale)
      Converts all of the characters in this String to upper case using the rules of the given Locale.
      Stringtrim()
      Returns a copy of the string, with leading and trailing whitespace omitted.
      static StringvalueOf(boolean b)
      Returns the string representation of the boolean argument.
      static StringvalueOf(char c)
      Returns the string representation of the char argument.
      static StringvalueOf(char[] data)
      Returns the string representation of the char array argument.
      static StringvalueOf(char[] data, int offset, int count)
      Returns the string representation of a specific subarray of the char array argument.
      static StringvalueOf(double d)
      Returns the string representation of the double argument.
      static StringvalueOf(float f)
      Returns the string representation of the float argument.
      static StringvalueOf(int i)
      Returns the string representation of the int argument.
      static StringvalueOf(long l)
      Returns the string representation of the long argument.
      static StringvalueOf(Object obj)
      Returns the string representation of the Object argument.





These notes are copyright Dr. Derek Molloy, School of Electronic Engineering, Dublin City University, Ireland 2013-present. Please contact him directly before reproducing any of the content in any way.
Comments