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.
Case mapping is based on the Unicode Standard version specified by the
Character
class.
Case mapping relies heavily on the information provided by the Unicode Consortium's Unicode 3.0 specification. The specification's UnicodeData.txt and SpecialCasing.txt files are used extensively to provide case mapping.
The Java language provides special support for the string concatenation operator ( + ), and for conversion of other objects to strings. String concatenation is implemented through the StringBuffer class and its append method. String conversions are implemented through the method toString, defined by Object and inherited by all classes in Java. For additional information on string concatenation and conversion, see Gosling, Joy, and Steele, The Java Language Specification .
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 | |
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static Comparator < String |
CASE_INSENSITIVE_ORDER
A Comparator that orders String objects as by compareToIgnoreCase. |
Constructor Summary | |
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String
() Initializes a newly created String object so that it represents an empty character sequence. |
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String
(byte[] bytes) Constructs a new String by decoding the specified array of bytes using the platform's default charset. |
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String
(byte[] ascii, int hibyte) Deprecated. This method does not properly convert bytes into characters. As of JDK 1.1, the preferred way to do this is via the String constructors that take a charset name or that use the platform's default charset. |
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String
(byte[] bytes, int offset, int length) Constructs a new String by decoding the specified subarray of bytes using the platform's default charset. |
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String
(byte[] ascii, int hibyte, int offset, int count) Deprecated. This method does not properly convert bytes into characters. As of JDK 1.1, the preferred way to do this is via the String constructors that take a charset name or that use the platform's default charset. |
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String
(byte[] bytes, int offset, int length,
String
charsetName) Constructs a new String by decoding the specified subarray of bytes using the specified charset. |
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String
(byte[] bytes,
String
charsetName) Constructs a new String by decoding the specified array of bytes using the specified charset. |
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String
(char[] value) Allocates a new String so that it represents the sequence of characters currently contained in the character array argument. |
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String
(char[] value, int offset, int count) Allocates a new String that contains characters from a subarray of the character array argument. |
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String
(int[] codePoints, int offset, int count)
Allocates a new String that contains characters from a subarray of the Unicode code point array argument. |
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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. |
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String
(
StringBuffer
buffer) Allocates a new string that contains the sequence of characters currently contained in the string buffer argument. |
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String
(
StringBuilder
Allocates a new string that contains the sequence of characters currently contained in the string builder argument. |
Method Summary | |
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char |
charAt
(int index) Returns the char value |
int |
codePointAt
(int index)
Returns the character (Unicode code point) at the specified index. |
|
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int |
codePointBefore
(int index)
Returns the character (Unicode code point) before the specified index. |
int |
compareTo
(
String
anotherString) Compares two strings lexicographically. |
int |
compareToIgnoreCase
(
String
str) Compares two strings lexicographically, ignoring case differences. |
String |
concat
(
String
str) Concatenates the specified string to the end of this string. |
boolean |
contains
(
String
Returns true if and only if this string contains the specified string. |
boolean |
contentEquals
(
StringBuffer
sb) Returns true if and only if this String represents the same sequence of characters as the specified StringBuffer . |
static String |
copyValueOf
(char[] data) Returns a String that represents the character sequence in the array specified. |
static String |
copyValueOf
(char[] data, int offset, int count) Returns a String that represents the character sequence in the array specified. |
boolean |
endsWith
(
String
suffix) Tests if this string ends with the specified suffix. |
boolean |
equals
(
Object
anObject) Compares this string to the specified object. |
boolean |
equalsIgnoreCase
(
String
anotherString) Compares this String to another String, ignoring case considerations. |
static String |
format
(
Locale
l,
String
format,
Object
Returns a formatted string using the specified locale, format string, and arguments. |
static String |
format
(
String
format,
Object
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. |
void |
getBytes
(int srcBegin, int srcEnd, byte[] dst, int dstBegin) Deprecated. This method does not properly convert characters into bytes. As of JDK 1.1, the preferred way to do this is via the the getBytes() method, which uses the platform's default charset. |
byte[] |
getBytes
(
String
charsetName) Encodes this String into a sequence of bytes using the named charset, storing the result into a new byte array. |
void |
getChars
(int srcBegin, int srcEnd, char[] dst, int dstBegin) Copies characters from this string into the destination character array. |
int |
hashCode
() Returns a hash code for this string. |
int |
indexOf
(int ch) Returns the index within this string of the first occurrence of the specified character. |
int |
indexOf
(int ch, int fromIndex) Returns the index within this string of the first occurrence of the specified character, starting the search at the specified index. |
int |
indexOf
(
String
str) Returns the index within this string of the first occurrence of the specified substring. |
int |
indexOf
(
String
str, int fromIndex) Returns the index within this string of the first occurrence of the specified substring, starting at the specified index. |
String |
intern
() Returns a canonical representation for the string object. |
int |
lastIndexOf
(int ch) Returns the index within this string of the last occurrence of the specified character. |
int |
lastIndexOf
(int ch, int fromIndex) Returns the index within this string of the last occurrence of the specified character, searching backward starting at the specified index. |
int |
lastIndexOf
(
String
str) Returns the index within this string of the rightmost occurrence of the specified substring. |
int |
lastIndexOf
(
String
str, int fromIndex) Returns the index within this string of the last occurrence of the specified substring, searching backward starting at the specified index. |
int |
length
() Returns the length of this string. |
boolean |
matches
(
String
regex) Tells whether or not this string matches the given regular expression . |
boolean |
regionMatches
(boolean ignoreCase, int toffset,
String
other, int ooffset, int len) Tests if two string regions are equal. |
boolean |
regionMatches
(int toffset,
String
other, int ooffset, int len) Tests if two string regions are equal. |
String |
replace
(char oldChar, char newChar) Returns a new string resulting from replacing all occurrences of oldChar in this string with newChar. |
String |
replace
(
String
target,
String
Replaces each substring of this string that matches the literal target string with the specified literal replacement string. |
String |
replaceAll
(
String
regex,
String
replacement) Replaces each substring of this string that matches the given regular expression with the given replacement. |
String |
replaceFirst
(
String
regex,
String
replacement) Replaces the first substring of this string that matches the given regular expression with the given replacement. |
String [] |
split
(
String
regex) Splits this string around matches of the given regular expression . |
String [] |
split
(
String
regex, int limit) Splits this string around matches of the given regular expression . |
boolean |
startsWith
(
String
prefix) Tests if this string starts with the specified prefix. |
boolean |
startsWith
(
String
prefix, int toffset) Tests if this string starts with the specified prefix beginning a specified index. |
CharSequence |
subSequence
(int beginIndex, int endIndex) Returns a new character sequence that is a subsequence of this sequence. |
String |
substring
(int beginIndex) Returns a new string that is a substring of this string. |
String |
substring
(int beginIndex, int endIndex) Returns a new string that is a substring of this string. |
char[] |
toCharArray
() Converts this string to a new character array. |
String |
toLowerCase
() Converts all of the characters in this String to lower case using the rules of the default locale. |
String |
toLowerCase
(
Locale
locale) Converts all of the characters in this String to lower case using the rules of the given Locale. |
String |
toString
() This object (which is already a string!) is itself returned. |
String |
toUpperCase
() Converts all of the characters in this String to upper case using the rules of the default locale. |
String |
toUpperCase
(
Locale
locale) Converts all of the characters in this String to upper case using the rules of the given Locale. |
String |
trim
() Returns a copy of the string, with leading and trailing whitespace omitted. |
static String |
valueOf
(boolean b) Returns the string representation of the boolean argument. |
static String |
valueOf
(char c) Returns the string representation of the char argument. |
static String |
valueOf
(char[] data) Returns the string representation of the char array argument. |
static String |
valueOf
(char[] data, int offset, int count) Returns the string representation of a specific subarray of the char array argument. |
static String |
valueOf
(double d) Returns the string representation of the double argument. |
static String |
valueOf
(float f) Returns the string representation of the float argument. |
static String |
valueOf
(int i) Returns the string representation of the int argument. |
static String |
valueOf
(long l) Returns the string representation of the long argument. |
static String |
valueOf
(
Object
obj) Returns the string representation of the Object argument. |
Methods inherited from class java.lang. Object |
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clone , finalize , getClass , notify , notifyAll , wait , wait , wait |
Methods inherited from interface java.lang. Comparable |
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compareTo |
Field Detail |
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public static final Comparator< String> CASE_INSENSITIVE_ORDER
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 |
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public String()
public String(String original)
public String(char[] value)
public String(char[] value, int offset, int count)
public String (int[] codePoints, int offset, int count)
public String(byte[] ascii, int hibyte, int offset, int count)
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.
public String(byte[] ascii, int hibyte)
c == (char)(((hibyte & 0xff) << 8) | (b & 0xff))
public String(byte[] bytes, int offset, int length, String charsetName) throws UnsupportedEncodingException
The behavior of this constructor when the given bytes are not valid in the given charset is unspecified. The CharsetDecoder class should be used when more control over the decoding process is required.
public String(byte[] bytes, String charsetName) throws UnsupportedEncodingException
The behavior of this constructor when the given bytes are not valid in the given charset is unspecified. The CharsetDecoder class should be used when more control over the decoding process is required.
public String(byte[] bytes, int offset, int length)
The behavior of this constructor when the given bytes are not valid in the default charset is unspecified. The CharsetDecoder class should be used when more control over the decoding process is required.
public String(byte[] bytes)
The behavior of this constructor when the given bytes are not valid in the default charset is unspecified. The CharsetDecoder class should be used when more control over the decoding process is required.
public String(StringBuffer buffer)
public String ( StringBuilder builder)
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.
Method Detail |
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public int length()
public char charAt(int index)
If the char value specified by the index is a surrogate , the surrogate value is returned.
public int codePointAt (int index)
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.
public int codePointBefore (int index)
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.
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
public void getBytes(int srcBegin, int srcEnd, byte[] dst, int dstBegin)
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
public byte[] getBytes(String charsetName) throws UnsupportedEncodingException
The behavior of this method when this string cannot be encoded in the given charset is unspecified. The CharsetEncoder class should be used when more control over the encoding process is required.
public byte[] getBytes()
The behavior of this method when this string cannot be encoded in the default charset is unspecified. The CharsetEncoder class should be used when more control over the encoding process is required.
public boolean equals(Object anObject)
public boolean contentEquals(StringBuffer sb)
public boolean equalsIgnoreCase(String anotherString)
Two characters c1 and c2 are considered the same, ignoring case if at least one of the following is true:
public int compareTo(String anotherString)
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, compareTo returns the difference of the lengths of the strings -- that is, the value:this.charAt(k)-anotherString.charAt(k)
this.length()-anotherString.length()
public intcompareTo(Objecto)
public int compareToIgnoreCase(String str)
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.
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:
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))
public boolean startsWith(String prefix, int toffset)
this.substring(toffset).startsWith(prefix)this.subString(toffset).startsWith(prefix)
public boolean startsWith(String prefix)
public boolean endsWith(String suffix)
public int hashCode()
using int arithmetic, where s[i] is the i th character of the string, n is the length of the string, and ^ indicates exponentiation. (The hash value of the empty string is zero.)s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1]
public int indexOf(int ch)
is true. For other values of ch, it is the smallest value k such that:this.charAt(k) == ch
is true. In either case, if no such character occurs in this string, then -1 is returned.this.codePointAt( k ) == ch
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. For values of ch in
returned--that is,
the
range from 0 to 0xFFFF (inclusive), this is the
smallest value
k
such that:
is true. For other values of ch, it is the smallest value k such that:(this.charAt(k) == ch) && (k >= fromIndex)
is true. In either case, if no such character occurs in this string at or after position fromIndex, then -1 is returned.(this.codePointAt( k ) == ch) && ( k >= fromIndex)
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).
public int lastIndexOf(int ch)
is true. For other values of ch, it is the largest value k such that:this.charAt(k) == ch
is true. In either case, if no such character occurs in this string, then -1 is returned. The String is searched backwards starting at the last character.this.codePointAt( k ) == ch
public int lastIndexOf(int ch, int fromIndex)
is true. For other values of ch, it is the largest value k such that:(this.charAt( k )this.charAt(k)== ch) && ( k(k<= fromIndex)
is true. In either case, if no such character occurs in this string at or before position fromIndex, then -1 is returned.(this.codePointAt( k ) == ch) && ( k <= fromIndex)
All indices are specified in char values (Unicode code units).
public int indexOf(String str)
is true.this.startsWith(str, k)
public int indexOf(String str, int fromIndex)
If no such value of k exists, then -1 is returned.k >= Math.min(fromIndex, str.length()) && this.startsWith(str, k)
public int lastIndexOf(String str)
is true.this.startsWith(str, k)
public int lastIndexOf(String str, int fromIndex)
If no such value of k exists, then -1 is returned.k <= Math.min(fromIndex, str.length()) && this.startsWith(str, k)
public String substring(int beginIndex)
Examples:
"unhappy".substring(2) returns "happy" "Harbison".substring(3) returns "bison" "emptiness".substring(9) returns "" (an empty string)
public String substring(int beginIndex, int endIndex)
Examples:
"hamburger".substring(4, 8) returns "urge" "smiles".substring(1, 5) returns "mile"
public CharSequence subSequence(int beginIndex, int endIndex)
An invocation of this method of the form
behaves in exactly the same way as the invocationstr.subSequence(begin, end)
This method is defined so that the String class can implement the CharSequence interface.str.substring(begin, end)
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"
public String replace(char oldChar, char 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)
public boolean matches(String regex)
An invocation of this method of the form str .matches( regex ) yields exactly the same result as the expression
Pattern . matches ( regex , str )
public boolean contains ( String s)
public String replaceFirst(String regex, String replacement)
An invocation of this method of the form str .replaceFirst( regex , repl ) yields exactly the same result as the expression
Pattern . compile ( regex ). matcher ( str ). replaceFirst ( repl )
public String replaceAll(String regex, String replacement)
An invocation of this method of the form str .replaceAll( regex , repl ) yields exactly the same result as the expression
Pattern . compile ( regex ). matcher ( str ). replaceAll ( repl )
public Stringreplace ( String target, String replacement)
public String[] split(String regex, int limit)
The array returned by this method contains each substring of this string that is terminated by another substring that matches the given expression or is terminated by the end of the string. The substrings in the array are in the order in which they occur in this string. If the expression does not match any part of the input then the resulting array has just one element, namely this string.
The limit parameter controls the number of times the pattern is applied and therefore affects the length of the resulting array. If the limit n is greater than zero then the pattern will be applied at most n - 1 times, the array's length will be no greater than n , and the array's last entry will contain all input beyond the last matched delimiter. If n is non-positive then the pattern will be applied as many times as possible and the array can have any length. If n is zero then the pattern will be applied as many times as possible, the array can have any length, and trailing empty strings will be discarded.
The string "boo:and:foo" , for example, yields the following results with these parameters:
Regex Limit Result : 2 { "boo", "and:foo" } : 5 { "boo", "and", "foo" } : -2 { "boo", "and", "foo" } o 5 { "b", "", ":and:f", "", "" } o -2 { "b", "", ":and:f", "", "" } o 0 { "b", "", ":and:f" }
An invocation of this method of the form str. split( regex , n ) yields the same result as the expression
Pattern . compile ( regex ) . split ( str , n )
public String[] split(String regex)
This method works as if by invoking the two-argument split method with the given expression and a limit argument of zero. Trailing empty strings are therefore not included in the resulting array.
The string "boo:and:foo" , for example, yields the following results with these expressions:
Regex Result : { "boo", "and", "foo" } o { "b", "", ":and:f" }
public String toLowerCase(Locale locale)
Examples of lowercase mappings are 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 |
(all) | French Fries | french fries | lowercased all chars in String |
(all) | lowercased all chars in String |
public String toLowerCase()
public String toUpperCase(Locale locale)
Examples of locale-sensitive and 1:M case mappings are 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 |
(all) | Fahrvergnügen | FAHRVERGNÜGEN |
public String 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()
public char[] toCharArray()
public static Stringformat ( String format, Object... args)
The locale always used is the one returned by Locale.getDefault() .
public static Stringformat ( Locale l, String format, Object... args)
public static String valueOf(Object obj)
public static String valueOf(char[] data)
public static String valueOf(char[] data, int offset, int count)
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.
public static String copyValueOf(char[] data, int offset, int count)
public static String copyValueOf(char[] data)
public static String valueOf(boolean b)
public static String valueOf(char c)
public static String valueOf(int i)
The representation is exactly the one returned by the Integer.toString method of one argument.
public static String valueOf(long l)
The representation is exactly the one returned by the Long.toString method of one argument.
public static String valueOf(float f)
The representation is exactly the one returned by the Float.toString method of one argument.
public static String valueOf(double d)
The representation is exactly the one returned by the Double.toString method of one argument.
public 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 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