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java.lang.Object | +--java.lang.String
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.
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.
Object.toString(),
StringBuffer,
StringBuffer.append(boolean),
StringBuffer.append(char),
StringBuffer.append(char[]),
StringBuffer.append(char[], int, int),
StringBuffer.append(int),
StringBuffer.append(long),
StringBuffer.append(java.lang.Object),
StringBuffer.append(java.lang.String)| Constructor Summary | |
String()
Initializes a newly created String object so that it
represents an empty character sequence. |
|
String(byte[] bytes)
Construct a new String by converting the specified array
of bytes using the platform's default character encoding. |
|
String(byte[] bytes,
int off,
int len)
Construct a new String by converting the specified
subarray of bytes using the platform's default character encoding. |
|
String(byte[] bytes,
int off,
int len,
String enc)
Construct a new String by converting the specified
subarray of bytes using the specified character encoding. |
|
String(byte[] bytes,
String enc)
Construct a new String by converting the specified array
of bytes using the specified character encoding. |
|
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 value)
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(String anotherString)
Compares two strings lexicographically. |
String |
concat(String str)
Concatenates the specified string to the end of this string. |
boolean |
endsWith(String suffix)
Tests if this string ends with the specified suffix. |
boolean |
equals(Object anObject)
Compares this string to the specified object. |
byte[] |
getBytes()
Convert this String into bytes according to the platform's
default character encoding, storing the result into a new byte array. |
byte[] |
getBytes(String enc)
Convert this String into bytes according to the specified
character encoding, 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 hashcode 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. |
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 |
length()
Returns the length of this string. |
boolean |
regionMatches(boolean ignoreCase,
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. |
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. |
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. |
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. |
String |
trim()
Removes white space from both ends of this string. |
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(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. |
| Methods inherited from class java.lang.Object |
getClass, notify, notifyAll, wait, wait, wait |
| Constructor Detail |
public String()
String object so that it
represents an empty character sequence.public String(String value)
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.value - a String.public String(char[] value)
String so that it represents the
sequence of characters currently contained in the character array
argument. The contents of the character array are copied; subsequent
modification of the character array does not affect the newly created
string.value - the initial value of the string.NullPointerException - if value is null.
public String(char[] value,
int offset,
int count)
String that contains characters from
a subarray of the character array argument. The offset
argument is the index of the first character of the subarray and
the count argument specifies the length of the
subarray. The contents of the subarray are copied; subsequent
modification of the character array does not affect the newly
created string.value - array that is the source of characters.offset - the initial offset.count - the length.IndexOutOfBoundsException - if the offset
and count arguments index characters outside
the bounds of the value array.NullPointerException - if value is
null.
public String(byte[] bytes,
int off,
int len,
String enc)
throws UnsupportedEncodingException
String by converting the specified
subarray of bytes using the specified character encoding. The length of
the new String is a function of the encoding, and hence may
not be equal to the length of the subarray.bytes - The bytes to be converted into charactersoff - Index of the first byte to convertlen - Number of bytes to convertenc - The name of a character encodingUnsupportedEncodingException - If the named encoding is not supported
public String(byte[] bytes,
String enc)
throws UnsupportedEncodingException
String by converting the specified array
of bytes using the specified character encoding. The length of the new
String is a function of the encoding, and hence may not be
equal to the length of the byte array.bytes - The bytes to be converted into charactersenc - The name of a supported character encodingUnsupportedEncodingException - If the named encoding is not supported
public String(byte[] bytes,
int off,
int len)
String by converting the specified
subarray of bytes using the platform's default character encoding. The
length of the new String is a function of the encoding, and
hence may not be equal to the length of the subarray.bytes - The bytes to be converted into charactersoff - Index of the first byte to convertlen - Number of bytes to convertpublic String(byte[] bytes)
String by converting the specified array
of bytes using the platform's default character encoding. The length of
the new String is a function of the encoding, and hence may
not be equal to the length of the byte array.bytes - The bytes to be converted into characterspublic String(StringBuffer buffer)
buffer - a StringBuffer.NullPointerException - If buffer is
null.| Method Detail |
public int length()
public char charAt(int index)
0 to length() - 1. The first character
of the sequence is at index 0, the next at index
1, and so on, as for array indexing.index - the index of the character.0.IndexOutOfBoundsException - if the index
argument is negative or not less than the length of this
string.
public void getChars(int srcBegin,
int srcEnd,
char[] dst,
int dstBegin)
The first character to be copied is at index srcBegin;
the last character to be copied is at index srcEnd-1
(thus the total number of characters to be copied is
srcEnd-srcBegin). The characters are copied into the
subarray of dst starting at index dstBegin
and ending at index:
dstbegin + (srcEnd-srcBegin) - 1
srcBegin - index of the first character in the string
to copy.srcEnd - index after the last character in the string
to copy.dst - the destination array.dstBegin - the start offset in the destination array.IndexOutOfBoundsException - If any of the following
is true:
srcBegin is negative.
srcBegin is greater than srcEnd
srcEnd is greater than the length of this
string
dstBegin is negative
dstBegin+(srcEnd-srcBegin) is larger than
dst.lengthNullPointerException - if dst is null
public byte[] getBytes(String enc)
throws UnsupportedEncodingException
String into bytes according to the specified
character encoding, storing the result into a new byte array.enc - A character-encoding nameUnsupportedEncodingException - If the named encoding is not supportedpublic byte[] getBytes()
String into bytes according to the platform's
default character encoding, storing the result into a new byte array.public boolean equals(Object anObject)
true if and only if the argument is not
null and is a String object that represents
the same sequence of characters as this object.equals in class ObjectanObject - the object to compare this String
against.true if the String are equal;
false otherwise.compareTo(java.lang.String)public int compareTo(String anotherString)
String object is compared lexicographically to the
character sequence represented by the argument string. The result is
a negative integer if this String object
lexicographically precedes the argument string. The result is a
positive integer if this String object lexicographically
follows the argument string. The result is zero if the strings
are equal; compareTo returns 0 exactly when
the equals(Object) method would return true.
This is the definition of lexicographic ordering. If two strings are
different, then either they have different characters at some index
that is a valid index for both strings, or their lengths are different,
or both. If they have different characters at one or more index
positions, let k be the smallest such index; then the string
whose character at position k has the smaller value, as
determined by using the < operator, lexicographically precedes the
other string. In this case, compareTo returns the
difference of the two character values at position k in
the two string -- that is, the value:
If there is no index position at which they differ, then the shorter string lexicographically precedes the longer string. In this case,this.charAt(k)-anotherString.charAt(k)
compareTo returns the difference of the lengths of the
strings -- that is, the value:
this.length()-anotherString.length()
anotherString - the String to be compared.0 if the argument string is equal to
this string; a value less than 0 if this string
is lexicographically less than the string argument; and a
value greater than 0 if this string is
lexicographically greater than the string argument.NullPointerException - if anotherString
is null.
public boolean regionMatches(boolean ignoreCase,
int toffset,
String other,
int ooffset,
int len)
A substring of this String object is compared to a substring of the argument other. The result is true if these substrings represent character sequences that are the same, ignoring case if and only if ignoreCase is true. The substring of this String object to be compared begins at index toffset and has length len. The substring of other to be compared begins at index ooffset and has length len. The result is false if and only if at least one of the following is true:
this.charAt(toffset+k) != other.charAt(ooffset+k)
and:Character.toLowerCase(this.charAt(toffset+k)) != Character.toLowerCase(other.charAt(ooffset+k))
Character.toUpperCase(this.charAt(toffset+k)) !=
Character.toUpperCase(other.charAt(ooffset+k))
ignoreCase - if true, ignore case when comparing
characters.toffset - the starting offset of the subregion in this
string.other - the string argument.ooffset - the starting offset of the subregion in the string
argument.len - the number of characters to compare.true if the specified subregion of this string
matches the specified subregion of the string argument;
false otherwise. Whether the matching is exact
or case insensitive depends on the ignoreCase
argument.
public boolean startsWith(String prefix,
int toffset)
prefix - the prefix.toffset - where to begin looking in the string.true if the character sequence represented by the
argument is a prefix of the substring of this object starting
at index toffset; false otherwise.
The result is false if toffset is
negative or greater than the length of this
String object; otherwise the result is the same
as the result of the expression
this.subString(toffset).startsWith(prefix)
NullPointerException - if prefix is
null.public boolean startsWith(String prefix)
prefix - the prefix.true if the character sequence represented by the
argument is a prefix of the character sequence represented by
this string; false otherwise.
Note also that true will be returned if the
argument is an empty string or is equal to this
String object as determined by the
equals(Object) method.NullPointerException - if prefix is
null.public boolean endsWith(String suffix)
suffix - the suffix.true if the character sequence represented by the
argument is a suffix of the character sequence represented by
this object; false otherwise. Note that the
result will be true if the argument is the
empty string or is equal to this String object
as determined by the equals(Object) method.NullPointerException - if suffix is
null.public int hashCode()
String object is computed as
usings[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1]
int arithmetic, where s[i] is the
ith character of the string, n is the length of
the string, and ^ indicates exponentiation.
(The hash value of the empty string is zero.)hashCode in class Objectpublic int indexOf(int ch)
ch occurs
in the character sequence represented by this String
object, then the index of the first such occurrence is returned --
that is, the smallest value k such that:
isthis.charAt(k) == ch
true. If no such character occurs in this string,
then -1 is returned.ch - a character.-1 if the character does not occur.
public int indexOf(int ch,
int fromIndex)
If a character with value ch occurs in the character
sequence represented by this String object at an index
no smaller than fromIndex, then the index of the first
such occurrence is returned--that is, the smallest value k
such that:
is true. If no such character occurs in this string at or after position(this.charAt(k) == ch) && (k >= fromIndex)
fromIndex, then -1 is returned.
There is no restriction on the value of fromIndex. If it
is negative, it has the same effect as if it were zero: this entire
string may be searched. If it is greater than the length of this
string, it has the same effect as if it were equal to the length of
this string: -1 is returned.
ch - a character.fromIndex - the index to start the search from.fromIndex, or -1
if the character does not occur.public int lastIndexOf(int ch)
is true. The String is searched backwards starting at the last character.this.charAt(k) == ch
ch - a character.-1 if the character does not occur.
public int lastIndexOf(int ch,
int fromIndex)
is true.this.charAt(k) == ch) && (k <= fromIndex)
ch - a character.fromIndex - the index to start the search from. There is no
restriction on the value of fromIndex. If it is
greater than or equal to the length of this string, it has
the same effect as if it were equal to one less than the
length of this string: this entire string may be searched.
If it is negative, it has the same effect as if it were -1:
-1 is returned.fromIndex, or -1
if the character does not occur before that point.public int indexOf(String str)
isthis.startsWith(str, k)
true.str - any string.-1 is returned.NullPointerException - if str is
null.
public int indexOf(String str,
int fromIndex)
isthis.startsWith(str, k) && (k >= fromIndex)
true.
There is no restriction on the value of fromIndex. If
it is negative, it has the same effect as if it were zero: this entire
string may be searched. If it is greater than the length of this
string, it has the same effect as if it were equal to the length of
this string: -1 is returned.
str - the substring to search for.fromIndex - the index to start the search from.fromIndex, then the index of the first character
of the first such substring is returned. If it does not occur
as a substring starting at fromIndex or beyond,
-1 is returned.NullPointerException - if str is
nullpublic String substring(int beginIndex)
Examples:
"unhappy".substring(2) returns "happy" "Harbison".substring(3) returns "bison" "emptiness".substring(9) returns "" (an empty string)
beginIndex - the beginning index, inclusive.IndexOutOfBoundsException - if
beginIndex is negative or larger than the
length of this String object.
public String substring(int beginIndex,
int endIndex)
beginIndex and
extends to the character at index endIndex - 1.
Thus the length of the substring is endIndex-beginIndex.
Examples:
"hamburger".substring(4, 8) returns "urge" "smiles".substring(1, 5) returns "mile"
beginIndex - the beginning index, inclusive.endIndex - the ending index, exclusive.IndexOutOfBoundsException - if the
beginIndex is negative, or
endIndex is larger than the length of
this String object, or
beginIndex is larger than
endIndex.public String concat(String str)
If the length of the argument string is 0, then this
String object is returned. Otherwise, a new
String object is created, representing a character
sequence that is the concatenation of the character sequence
represented by this String object and the character
sequence represented by the argument string.
Examples:
"cares".concat("s") returns "caress"
"to".concat("get").concat("her") returns "together"
str - the String that is concatenated to the end
of this String.NullPointerException - if str is
null.
public String replace(char oldChar,
char newChar)
oldChar in this string with newChar.
If the character oldChar does not occur in the
character sequence represented by this String object,
then a reference to this String object is returned.
Otherwise, a new String object is created that
represents a character sequence identical to the character sequence
represented by this String object, except that every
occurrence of oldChar is replaced by an occurrence
of newChar.
Examples:
"mesquite in your cellar".replace('e', 'o')
returns "mosquito in your collar"
"the war of baronets".replace('r', 'y')
returns "the way of bayonets"
"sparring with a purple porpoise".replace('p', 't')
returns "starring with a turtle tortoise"
"JonL".replace('q', 'x') returns "JonL" (no change)
oldChar - the old character.newChar - the new character.oldChar with newChar.public String toLowerCase()
Character.toLowerCase(char),
toUpperCase()public String toUpperCase()
Character.toLowerCase(char),
toUpperCase()public String trim()
If this String object represents an empty character
sequence, or the first and last characters of character sequence
represented by this String object both have codes
greater than '\u0020' (the space character), then a
reference to this String object is returned.
Otherwise, if there is no character with a code greater than
'\u0020' in the string, then a new
String object representing an empty string is created
and returned.
Otherwise, let k be the index of the first character in the
string whose code is greater than '\u0020', and let
m be the index of the last character in the string whose code
is greater than '\u0020'. A new String
object is created, representing the substring of this string that
begins with the character at index k and ends with the
character at index m-that is, the result of
this.substring(k, m+1).
This method may be used to trim whitespace from the beginning and end of a string; in fact, it trims all ASCII control characters as well.
public String toString()
toString in class Objectpublic char[] toCharArray()
public static String valueOf(Object obj)
Object argument.obj - an Object.null, then a string equal to
"null"; otherwise, the value of
obj.toString() is returned.Object.toString()public static String valueOf(char[] data)
char array
argument. The contents of the character array are copied; subsequent
modification of the character array does not affect the newly
created string.data - a char array.
public static String valueOf(char[] data,
int offset,
int count)
char array argument.
The offset argument is the index of the first
character of the subarray. The count argument
specifies the length of the subarray. The contents of the subarray
are copied; subsequent modification of the character array does not
affect the newly created string.
data - the character array.offset - the initial offset into the value of the
String.count - the length of the value of the String.NullPointerException - if data is
null.IndexOutOfBoundsException - if offset is
negative, or count is negative, or
offset+count is larger than
data.length.public static String valueOf(boolean b)
boolean argument.b - a boolean.true, a string equal to
"true" is returned; otherwise, a string equal to
"false" is returned.public static String valueOf(char c)
char
argument.c - a char.1 containing
as its single character the argument c.public static String valueOf(int i)
int argument.
The representation is exactly the one returned by the
Integer.toString method of one argument.
i - an int.int argument.Integer.toString(int, int)public static String valueOf(long l)
long argument.
The representation is exactly the one returned by the
Long.toString method of one argument.
l - a long.long argument.Long.toString(long)
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