java.lang.StringString 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(or 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.
Unless otherwise noted, passing a null argument to a constructor or method in this class will cause a NullPointerException to be thrown.
A 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).
| Field Summary | ||
static Comparator<String> |
CASE_INSENSITIVE_ORDER A Comparator that orders String objects as by
compareToIgnoreCase. |
|
| 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. |
||
| 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. |
||
| 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, int offset, int length, java.nio.charset.Charset charset) 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(byte[] bytes, java.nio.charset.Charset charset) 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 | ||
char |
charAt(int index) Returns the char value at the
specified index. |
|
int |
codePointAt(int index) Returns the character (Unicode code point) at the specified
index. |
|
int |
codePointBefore(int index) Returns the character (Unicode code point) before the specified
index. |
|
int |
codePointCount(int beginIndex, int endIndex) Returns the number of Unicode code points in the specified text
range of this String. |
|
int |
compareTo(String anotherString) Compares two strings lexicographically. |
|
int |
compareToIgnoreCase(String str) Compares two strings lexicographically, ignoring case
differences. |
|
| concat(String str) Concatenates the specified string to the end of this string. |
||
boolean |
contains(CharSequence s) Returns true if and only if this string contains the specified
sequence of char values. |
|
boolean |
contentEquals(CharSequence cs) Compares this string to the specified CharSequence. |
|
boolean |
contentEquals(StringBuffer sb) Compares this string to 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. |
|
static String |
format(String format, Object... args) Returns a formatted string using the specified format string and
arguments. |
|
static String |
format(Locale l, String format, Object... args) Returns a formatted string using the specified locale, 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. |
|
void |
getBytes(int srcBegin, int srcEnd, byte[] dst, int dstBegin) Deprecated. This method does not properly convert characters into
bytes. |
|
byte[] |
getBytes(String charsetName) Encodes this String into a sequence of bytes using the named
charset, storing the result into a new byte array. |
|
byte[] |
getBytes(java.nio.charset.Charset charset) Encodes this String into a sequence of bytes using the given
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. |
|
| intern() Returns a canonical representation for the string object. |
||
boolean |
isEmpty() Returns true if, and only if, length() is 0. |
|
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. |
|
int |
offsetByCodePoints(int index, int codePointOffset) Returns the index within this String that is
offset from the given index by
codePointOffset code points. |
|
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. |
|
| replace(char oldChar, char newChar) Returns a new string resulting from replacing all occurrences of
oldChar in this string with newChar. |
||
| replace(CharSequence target, CharSequence replacement) Replaces each substring of this string that matches the literal target
sequence with the specified literal replacement sequence. |
||
| replaceAll(String regex, String replacement) Replaces each substring of this string that matches the given regular expression with the
given replacement. |
||
| 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 the substring of this string beginning at the
specified index starts with the specified prefix. |
|
| subSequence(int beginIndex, int endIndex) Returns a new character sequence that is a subsequence of this sequence. |
||
| substring(int beginIndex) Returns a new string that is a substring of this 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. |
|
| toLowerCase() Converts all of the characters in this String to lower
case using the rules of the default locale. |
||
| toLowerCase(Locale locale) Converts all of the characters in this String to lower
case using the rules of the given Locale. |
||
| toString() This object (which is already a string!) is itself returned. |
||
| toUpperCase() Converts all of the characters in this String to upper
case using the rules of the default locale. |
||
| toUpperCase(Locale locale) Converts all of the characters in this String to upper
case using the rules of the given Locale. |
||
| 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(Object obj) Returns the string representation of the Object argument. |
|
static String |
valueOf(long l) Returns the string representation of the long argument. |
|
| Methods inherited from class java.lang.Object |
| clone, finalize, getClass, notify, notifyAll, wait, wait, wait |
String objects as by
compareToIgnoreCase. This comparator is serializable.
Note that this Comparator does not take locale into account, and will result in an unsatisfactory ordering for certain locales. The java.text package provides Collators to allow locale-sensitive ordering.
The offset argument is the index of the first byte of the subarray, and the count argument specifies the length of the subarray.
Each byte in the subarray is converted to a char as specified in the method above.
c == (char)(((hibyte & 0xff) << 8)
| (b & 0xff))
The behavior of this constructor when the given bytes are not valid in the given charset is unspecified. The java.nio.charset.CharsetDecoder class should be used when more control over the decoding process is required.
This method always replaces malformed-input and unmappable-character sequences with this charset's default replacement string. The java.nio.charset.CharsetDecoder class should be used when more control over the decoding process is required.
The behavior of this constructor when the given bytes are not valid in the given charset is unspecified. The java.nio.charset.CharsetDecoder class should be used when more control over the decoding process is required.
This method always replaces malformed-input and unmappable-character sequences with this charset's default replacement string. The java.nio.charset.CharsetDecoder class should be used when more control over the decoding process is required.
The behavior of this constructor when the given bytes are not valid in the default charset is unspecified. The java.nio.charset.CharsetDecoder class should be used when more control over the decoding process is required.
The behavior of this constructor when the given bytes are not valid in the default charset is unspecified. The java.nio.charset.CharsetDecoder class should be used when more control over the decoding process is required.
This constructor is provided to ease migration to StringBuilder. Obtaining a string from a string builder via the toString method is likely to run faster and is generally preferred.
char value at the
specified index. An index ranges from 0 to
length() - 1. The first char value of the sequence
is at index 0, the next at index 1,
and so on, as for array indexing.
If the char value specified by the index is a
surrogate, the surrogate
value is returned.
char value.char value at the specified index of this string.
The first char value is at index 0.index
argument is negative or not less than the length of this
string.char values
(Unicode code units) and ranges from 0 to
length() - 1.
If the char value specified at the given index
is in the high-surrogate range, the following index is less
than the length of this String, and the
char value at the following index is in the
low-surrogate range, then the supplementary code point
corresponding to this surrogate pair is returned. Otherwise,
the char value at the given index is returned.
char valuesindexindex
argument is negative or not less than the length of this
string.char values
(Unicode code units) and ranges from 1 to length.
If the char value at (index - 1)
is in the low-surrogate range, (index - 2) is not
negative, and the char value at (index -
2) is in the high-surrogate range, then the
supplementary code point value of the surrogate pair is
returned. If the char value at index -
1 is an unpaired low-surrogate or a high-surrogate, the
surrogate value is returned.
index
argument is less than 1 or greater than the length
of this string.String. The text range begins at the
specified beginIndex and extends to the
char at index endIndex - 1. Thus the
length (in chars) of the text range is
endIndex-beginIndex. Unpaired surrogates within
the text range count as one code point each.char of
the text range.char of
the text range.beginIndex is negative, or endIndex
is larger than the length of this String, or
beginIndex is larger than endIndex.String that is
offset from the given index by
codePointOffset code points. Unpaired surrogates
within the text range given by index and
codePointOffset count as one code point each.Stringindex
is negative or larger then the length of this
String, or if codePointOffset is positive
and the substring starting with index has fewer
than codePointOffset code points,
or if codePointOffset is negative and the substring
before index has fewer than the absolute value
of codePointOffset code points.
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 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.lengthThe first character to be copied is at index srcBegin; the last character to be copied is at index srcEnd-1. The total number of characters to be copied is srcEnd-srcBegin. The characters, converted to bytes, are copied into the subarray of dst starting at index dstBegin and ending at index:
dstbegin + (srcEnd-srcBegin) - 1
The behavior of this method when this string cannot be encoded in the given charset is unspecified. The java.nio.charset.CharsetEncoder class should be used when more control over the encoding process is required.
This method always replaces malformed-input and unmappable-character sequences with this charset's default replacement byte array. The java.nio.charset.CharsetEncoder class should be used when more control over the encoding process is required.
The behavior of this method when this string cannot be encoded in the default charset is unspecified. The java.nio.charset.CharsetEncoder class should be used when more control over the encoding process is required.
Two characters c1 and c2 are considered the same ignoring case if at least one of the following is true:
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()
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.compareTo with normalized versions of the strings
where case differences have been eliminated by calling
Character.toLowerCase(Character.toUpperCase(character)) on
each character.
Note that this method does not take locale into account, and will result in an unsatisfactory ordering for certain locales. The java.text package provides collators to allow locale-sensitive ordering.
String to be compared.A substring of this String object is compared to a substring of the argument other. The result is true if these substrings represent identical character sequences. 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:
true if the specified subregion of this string
exactly matches the specified subregion of the string argument;
false otherwise.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)
Character.toLowerCase(this.charAt(toffset+k)) !=
Character.toLowerCase(other.charAt(ooffset+k))
and:
Character.toUpperCase(this.charAt(toffset+k)) !=
Character.toUpperCase(other.charAt(ooffset+k))
true, ignore case when comparing
characters.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.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)
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.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.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.)ch occurs in the character sequence represented by
this String object, then the index (in Unicode
code units) of the first such occurrence is returned. For
values of ch in the range from 0 to 0xFFFF
(inclusive), this is the smallest value k such that:
is true. For other values ofthis.charAt(k) == ch
ch, it is the
smallest value k such that:
is true. In either case, if no such character occurs in this string, thenthis.codePointAt(k) == ch
-1 is returned.-1 if the character does not occur.
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. For values
of ch in the range from 0 to 0xFFFF (inclusive),
this is the smallest value k such that:
is true. For other values of(this.charAt(k) == ch) && (k >= fromIndex)
ch, it is the
smallest value k such that:
is true. In either case, if no such character occurs in this string at or after position(this.codePointAt(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.
All indices are specified in char values
(Unicode code units).
fromIndex, or -1
if the character does not occur.ch in the
range from 0 to 0xFFFF (inclusive), the index (in Unicode code
units) returned is the largest value k such that:
is true. For other values ofthis.charAt(k) == ch
ch, it is the
largest value k such that:
is true. In either case, if no such character occurs in this string, thenthis.codePointAt(k) == ch
-1 is returned. The
String is searched backwards starting at the last
character.-1 if the character does not occur.ch in the range
from 0 to 0xFFFF (inclusive), the index returned is the largest
value k such that:
is true. For other values of(this.charAt(k) == ch) && (k <= fromIndex)
ch, it is the
largest value k such that:
is true. In either case, if no such character occurs in this string at or before position(this.codePointAt(k) == ch) && (k <= fromIndex)
fromIndex, then
-1 is returned.
All indices are specified in char values
(Unicode code units).
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.isthis.startsWith(str, k)
true.-1 is returned.
k >= Math.min(fromIndex, this.length()) && this.startsWith(str, k)
If no such value of k exists, then -1 is returned.this.length().
The returned index is the largest value k such that
is true.this.startsWith(str, k)
-1 is returned.
k <= Math.min(fromIndex, this.length()) && this.startsWith(str, k)
If no such value of k exists, then -1 is returned.Examples:
"unhappy".substring(2) returns "happy" "Harbison".substring(3) returns "bison" "emptiness".substring(9) returns "" (an empty string)