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 concatentation 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.
Field Detail |
private char[] value
private int offset
private int count
private int hash
private static ThreadLocal btcConverter
private static final long serialVersionUID
private static final ObjectStreamField[] serialPersistentFields
TC_STRING
(utf String)
The String is written by method DataOutput.writeUTF
. A new handle is generated to refer to all future references to the string instance within the stream.public static final Comparator CASE_INSENSITIVE_ORDER
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.
Constructor Detail |
public String()
String
object so that it represents an empty character sequence.public String(String original)
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[] ascii, int hibyte, int offset, int count)
String
constructors that take a character-encoding name or that use the platform's default encoding.String
constructed from a subarray of an array of 8-bit integer values. 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.
ascii
- the bytes to be converted to characters.hibyte
- the top 8 bits of each 16-bit Unicode character.offset
- the initial offset.count
- the length.IndexOutOfBoundsException
- if the offset
or count
argument is invalid.NullPointerException
- if ascii
is null
.public String(byte[] ascii, int hibyte)
String
constructors that take a character-encoding name or that use the platform's default encoding.String
containing characters constructed from an array of 8-bit integer values. Each character cin the resulting string is constructed from the corresponding component b in the byte array such that: c == (char)(((hibyte & 0xff) << 8) | (b & 0xff))
ascii
- the bytes to be converted to characters.hibyte
- the top 8 bits of each 16-bit Unicode character.NullPointerException
- If ascii
is null
.private String(byte[] bytes, int offset, int length, ByteToCharConverter btc)
String
by converting the specified subarray of bytes using the specified character-encoding converter. 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 charactersoffset
- Index of the first byte to convertlength
- Number of bytes to convertbtc
- A ByteToCharConverterIndexOutOfBoundsException
- if the offset
and count
arguments index characters outside the bounds of the value
array.public String(byte[] bytes, int offset, int length, String enc)
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 charactersoffset
- Index of the first byte to convertlength
- Number of bytes to convertenc
- The name of a supported character encodingUnsupportedEncodingException
- if the named encoding is not supportedIndexOutOfBoundsException
- if the offset
and count
arguments index characters outside the bounds of the value
array.public String(byte[] bytes, String enc)
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 supportedpublic String(byte[] bytes, int offset, int length)
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 charactersoffset
- Index of the first byte to convertlength
- 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 |
private static ByteToCharConverter getBTCConverter(String encoding)
ByteToCharConverter
that uses the specified encoding. For efficiency a cache is maintained that holds the last used converter.enc
- The name of a character encodingUnsupportedEncodingException
- If the named encoding is not supportedprivate static CharToByteConverter getCTBConverter(String encoding)
CharToByteConverter
that uses the specified encoding. For efficiency a cache is maintained that holds the last used converter.enc
- The name of a character encodingUnsupportedEncodingException
- If the named encoding is not supportedpublic 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.length
NullPointerException
- if dst
is null
public void getBytes(int srcBegin, int srcEnd, byte[] dst, int dstBegin)
getBytes(String enc)
method, which takes a character-encoding name, or the getBytes()
method, which uses the platform's default encoding. The 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
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.length
NullPointerException
- if dst
is null
private byte[] getBytes(CharToByteConverter ctb)
ctb
- A CharToByteConverterpublic byte[] getBytes(String enc)
String
into bytes according to the specified character encoding, storing the result into a new byte array.enc
- The name of a supported character encodingUnsupportedEncodingException
- 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.anObject
- the object to compare this String
against.true
if the String
are equal; false
otherwise.public boolean equalsIgnoreCase(String anotherString)
String
to another String
, ignoring case considerations. Two strings are considered equal ignoring case if they are of the same length, and corresponding characters in the two strings are equal ignoring case. Two characters c1
and c2
are considered the same, ignoring case if at least one of the following is true:
==
operator). anotherString
- the String
to compare this String
against.true
if the argument is not null
and the String
s are equal, ignoring case; false
otherwise.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 {@link #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.java.lang.NullPointerException
- if anotherString
is null
.public int compareTo(Object o)
compareTo(String)
. Otherwise, it throws a ClassCastException
(as Strings are comparable only to other Strings).o
- the Object
to be compared.0
if the argument is a string lexicographically equal to this string; a value less than 0
if the argument is a string lexicographically greater than this string; and a value greater than 0
if the argument is a string lexicographically less than this string.ClassCastException
- if the argument is not a String
.public int compareToIgnoreCase(String str)
this.toUpperCase().toLowerCase().compareTo( str.toUpperCase().toLowerCase())
. 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.
str
- the String
to be compared.public boolean regionMatches(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 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:
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 exactly matches the specified subregion of the string argument; false
otherwise.java.lang.NullPointerException
- if other 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)
java.lang.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 {@link #equals(Object)} method.java.lang.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 {@link #equals(Object)} method.java.lang.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.)public 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. @param ch a character. @param fromIndex the index to start the search from. There is no restriction on the value ofthis.charAt(k) == ch) && (k <= fromIndex) *
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.
@return the index of the last occurrence of the character in the
character sequence represented by this object that is less
than or equal to 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.java.lang.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.java.lang.NullPointerException
- if str
is null
public int lastIndexOf(String str)
this.length()
. The returned index is the largest value k such that is true.this.startsWith(str, k)
str
- the substring to search for.-1
is returned.java.lang.NullPointerException
- if str
is null
.public int lastIndexOf(String str, int fromIndex)
fromIndex
. That is, the index returned is the largest value k such that: @param str the substring to search for. @param fromIndex the index to start the search from. There is no restriction on the value of fromIndex. 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: this entire string may be searched. If it is negative, it has the same effect as if it were -1: -1 is returned. @return If the string argument occurs one or more times as a substring within this object at a starting index no greater thanthis.startsWith(str, k) && (k <= fromIndex) *
fromIndex
, then the index of the first character of
the last such substring is returned. If it does not occur as a
substring starting at fromIndex
or earlier,
-1
is returned.
@exception java.lang.NullPointerException if str
is
null
.
public 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
.java.lang.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(Locale locale)
String
to lower case using the rules of the given Locale
. Usually, the characters are converted by calling Character.toLowerCase
. Exceptions to this rule are listed in the following table:
Language Code of Locale | Upper Case | Lower Case | Description |
---|---|---|---|
tr (Turkish) | \u0130 | \u0069 | capital letter I with dot above -> small letter i |
tr (Turkish) | \u0049 | \u0131 | capital letter I -> small letter dotless i |
locale
- use the case transformation rules for this localepublic String toLowerCase()
String
to lower case using the rules of the default locale, which is returned by Locale.getDefault
. If no character in the string has a different lowercase version, based on calling the toLowerCase
method defined by Character
, then the original string is returned.
Otherwise, this method creates a new String
object that represents a character sequence identical in length to the character sequence represented by this String object, with every character equal to the result of applying the method Character.toLowerCase
to the corresponding character of this String
object.
Examples:
"French Fries".toLowerCase() returns "french fries" "".toLowerCase() returns "
"
public String toUpperCase(Locale locale)
String
to upper case using the rules of the given locale. Usually, the characters are converted by calling Character.toUpperCase
. Exceptions to this rule are listed in the following table:
Language Code of Locale | Lower Case | Upper Case | Description |
---|---|---|---|
tr (Turkish) | \u0069 | \u0130 | small letter i -> capital letter I with dot above |
tr (Turkish) | \u0131 | \u0049 | small letter dotless i -> capital letter I |
(all) | \u00df | \u0053 \u0053 | small letter sharp s -> two letters: SS |
locale
- use the case transformation rules for this localepublic String toUpperCase()
String
to upper case using the rules of the default locale, which is returned by Locale.getDefault
. If no character in this string has a different uppercase version, based on calling the toUpperCase
method defined by Character
, then the original string is returned.
Otherwise, this method creates a new String
object representing a character sequence identical in length to the character sequence represented by this String
object and with every character equal to the result of applying the method Character.toUpperCase
to the corresponding character of this String
object.
Examples:
"Fahrvergnьgen".toUpperCase() returns "FAHRVERGNЬGEN" "Visit Ljubinje!".toUpperCase() returns "VISIT LJUBINJE!"
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 {@link Character#isSpace(char) whitespace} from the beginning and end of a string; in fact, it trims all ASCII control characters as well.
public String toString()
public 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.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 copyValueOf(char[] data, int offset, int count)
data
- the character array.offset
- initial offset of the subarray.count
- length of the subarray.String
that contains the characters of the specified subarray of the character array.public static String copyValueOf(char[] data)
data
- the character array.String
that contains the characters of the character array.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.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.public static String valueOf(float f)
float
argument. The representation is exactly the one returned by the Float.toString
method of one argument.
f
- a float
.float
argument.public static String valueOf(double d)
double
argument. The representation is exactly the one returned by the Double.toString
method of one argument.
d
- a double
.double
argument.public native String intern()
A pool of strings, initially empty, is maintained privately by the class String
.
When the intern method is invoked, if the pool already contains a string equal to this String
object as determined by the {@link #equals(Object)} method, then the string from the pool is returned. Otherwise, this String
object is added to the pool and a reference to this String
object is returned.
It follows that for any two strings s
and t
, s.intern() == t.intern()
is true
if and only if s.equals(t)
is true
.
All literal strings and string-valued constant expressions are interned. String literals are defined in §3.10.5 of the Java Language Specification