public final class

String

extends Object
implements CharSequence
java.lang.Object
   ↳ java.lang.String

Class Overview

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 The Java Language Specification.

See Also

Summary

Public Constructors
String()
Initializes a newly created String object so that it represents an empty character sequence.
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(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(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(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)
Construct a new String by converting the specified array of bytes using the platform's default character encoding.
String(StringBuffer buffer)
Allocates a new string that contains the sequence of characters currently contained in the string buffer argument.
Public Methods
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(String enc)
Convert this String into bytes according to the specified character encoding, storing the result into a new byte array.
byte[] getBytes()
Convert this String into bytes according to the platform's default 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, int fromIndex)
Returns the index within this string of the first occurrence of the specified substring, starting at the specified index.
int indexOf(String str)
Returns the index within this string of the first occurrence of the specified substring.
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, int toffset)
Tests if this string starts with the specified prefix beginning a specified index.
boolean startsWith(String prefix)
Tests if this string starts with the specified prefix.
CharSequence subSequence(int start, int end)
Returns a new character sequence that is a subsequence of this sequence.
String substring(int beginIndex, int endIndex)
Returns a new string that is a substring of this string.
String substring(int beginIndex)
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(double d)
Returns the string representation of the double argument.
static String valueOf(char c)
Returns the string representation of the char argument.
static String valueOf(long l)
Returns the string representation of the long 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(Object obj)
Returns the string representation of the Object 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(char[] data)
Returns the string representation of the char array argument.
[Expand]
Inherited Methods
From class java.lang.Object
From interface java.lang.CharSequence

Public Constructors

public String ()

Initializes a newly created String object so that it represents an empty character sequence.

public 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.

Parameters
value a String.

public String (char[] value)

Allocates a new 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.

Parameters
value the initial value of the string.
Throws
NullPointerException if value is null.

public String (char[] value, int offset, int count)

Allocates a new 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.

Parameters
value array that is the source of characters.
offset the initial offset.
count the length.
Throws
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)

Construct a new 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.

Parameters
bytes The bytes to be converted into characters
off Index of the first byte to convert
len Number of bytes to convert
enc The name of a character encoding
Throws
UnsupportedEncodingException If the named encoding is not supported

public String (byte[] bytes, String enc)

Construct a new 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.

Parameters
bytes The bytes to be converted into characters
enc The name of a supported character encoding
Throws
UnsupportedEncodingException If the named encoding is not supported

public 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. The length of the new String is a function of the encoding, and hence may not be equal to the length of the subarray.

Parameters
bytes The bytes to be converted into characters
off Index of the first byte to convert
len Number of bytes to convert

public String (byte[] bytes)

Construct a new 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.

Parameters
bytes The bytes to be converted into characters

public String (StringBuffer buffer)

Allocates a new string that contains the sequence of characters currently contained in the string buffer argument. The contents of the string buffer are copied; subsequent modification of the string buffer does not affect the newly created string.

Parameters
buffer a StringBuffer.
Throws
NullPointerException If buffer is null.

Public Methods

public char charAt (int index)

Returns the character at the specified index. An index ranges from 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.

Parameters
index the index of the character.
Returns
  • the character at the specified index of this string. The first character is at index 0.
Throws
IndexOutOfBoundsException if the index argument is negative or not less than the length of this string.

public int compareTo (String anotherString)

Compares two strings lexicographically. The comparison is based on the Unicode value of each character in the strings. The character sequence represented by this 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: 

 this.charAt(k) - anotherString.charAt(k)
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.length() - anotherString.length()

Parameters
anotherString the String to be compared.
Returns
  • the value 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.
Throws
NullPointerException if anotherString is null.

public String concat (String str)

Concatenates the specified string to the end of this string.

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"

Parameters
str the String that is concatenated to the end of this String.
Returns
  • a string that represents the concatenation of this object's characters followed by the string argument's characters.
Throws
NullPointerException if str is null.

public boolean endsWith (String suffix)

Tests if this string ends with the specified suffix.

Parameters
suffix the suffix.
Returns
  • 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.
Throws
NullPointerException if suffix is null.

public boolean equals (Object anObject)

Compares this string to the specified object. The result is 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.

Parameters
anObject the object to compare this String against.
Returns
  • true if the String are equal; false otherwise.
See Also

public byte[] getBytes (String enc)

Convert this String into bytes according to the specified character encoding, storing the result into a new byte array.

Parameters
enc A character-encoding name
Returns
  • The resultant byte array
Throws
UnsupportedEncodingException If the named encoding is not supported

public byte[] getBytes ()

Convert this String into bytes according to the platform's default character encoding, storing the result into a new byte array.

Returns
  • the resultant byte array.

public void getChars (int srcBegin, int srcEnd, char[] dst, int dstBegin)

Copies characters from this string into the destination character array.

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

Parameters
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.
Throws
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 int hashCode ()

Returns a hashcode for this string. The hashcode for a String object is computed as 

 s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1]
using 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.)

Returns
  • a hash code value for this object.

public int indexOf (int ch)

Returns the index within this string of the first occurrence of the specified character. If a character with value 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: 

 this.charAt(k) == ch
is true. If no such character occurs in this string, then -1 is returned.

Parameters
ch a character.
Returns
  • the index of the first occurrence of the character in the character sequence represented by this object, or -1 if the character does not occur.

public 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.

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: 

 (this.charAt(k) == ch) && (k >= fromIndex)
is true. If no such character occurs in this string at or after position 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.

Parameters
ch a character.
fromIndex the index to start the search from.
Returns
  • the index of the first occurrence of the character in the character sequence represented by this object that is greater than or equal to fromIndex, or -1 if the character does not occur.

public 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. The integer returned is the smallest value k such that: 

 this.startsWith(str, k) && (k >= fromIndex)
is 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.

Parameters
str the substring to search for.
fromIndex the index to start the search from.
Returns
  • If the string argument occurs as a substring within this object at a starting index no smaller than 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.
Throws
NullPointerException if str is null

public int indexOf (String str)

Returns the index within this string of the first occurrence of the specified substring. The integer returned is the smallest value k such that: 

 this.startsWith(str, k)
is true.

Parameters
str any string.
Returns
  • if the string argument occurs as a substring within this object, then the index of the first character of the first such substring is returned; if it does not occur as a substring, -1 is returned.
Throws
NullPointerException if str is null.

public int lastIndexOf (int ch)

Returns the index within this string of the last occurrence of the specified character. That is, the index returned is the largest value k such that: 

 this.charAt(k) == ch
is true. The String is searched backwards starting at the last character.

Parameters
ch a character.
Returns
  • the index of the last occurrence of the character in the character sequence represented by this object, or -1 if the character does not occur.

public 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. That is, the index returned is the largest value k such that: 

 this.charAt(k) == ch) && (k <= fromIndex)
is true.

Parameters
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.
Returns
  • 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 length ()

Returns the length of this string. The length is equal to the number of 16-bit Unicode characters in the string.

Returns
  • the length of the sequence of characters represented by this object.

public boolean regionMatches (boolean ignoreCase, int toffset, String other, int ooffset, int len)

Tests if two string regions are equal.

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:

  • toffset is negative.
  • ooffset is negative.
  • toffset+len is greater than the length of this String object.
  • ooffset+len is greater than the length of the other argument.
  • There is some nonnegative integer k less than len such that: 
     this.charAt(toffset + k) != other.charAt(ooffset + k)
  • ignoreCase is true and there is some nonnegative integer k less than len such that: 
     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))

Parameters
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.
Returns
  • 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 String replace (char oldChar, char newChar)

Returns a new string resulting from replacing all occurrences of 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)

Parameters
oldChar the old character.
newChar the new character.
Returns
  • a string derived from this string by replacing every occurrence of oldChar with newChar.

public boolean startsWith (String prefix, int toffset)

Tests if this string starts with the specified prefix beginning a specified index.

Parameters
prefix the prefix.
toffset where to begin looking in the string.
Returns
  • 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)
Throws
NullPointerException if prefix is null.

public boolean startsWith (String prefix)

Tests if this string starts with the specified prefix.

Parameters
prefix the prefix.
Returns
  • 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.
Throws
NullPointerException if prefix is null.

public CharSequence subSequence (int start, int end)

Returns a new character sequence that is a subsequence of this sequence.

An invocation of this method of the form 

 str.subSequence(begin, end)
behaves in exactly the same way as the invocation 
 str.substring(begin, end)
This method is defined so that the String class can implement the CharSequence interface.

Parameters
start the begin index, inclusive.
end the end index, exclusive.
Returns
  • the specified subsequence.
Throws
IndexOutOfBoundsException if beginIndex or endIndex are negative, if endIndex is greater than length(), or if beginIndex is greater than startIndex

public String substring (int beginIndex, int endIndex)

Returns a new string that is a substring of this string. The substring begins at the specified 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"

Parameters
beginIndex the beginning index, inclusive.
endIndex the ending index, exclusive.
Returns
  • the specified substring.
Throws
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 substring (int beginIndex)

Returns a new string that is a substring of this string. The substring begins with the character at the specified index and extends to the end of this string.

Examples: 

 "unhappy".substring(2) returns "happy"
 "Harbison".substring(3) returns "bison"
 "emptiness".substring(9) returns "" (an empty string)

Parameters
beginIndex the beginning index, inclusive.
Returns
  • the specified substring.
Throws
IndexOutOfBoundsException if beginIndex is negative or larger than the length of this String object.

public char[] toCharArray ()

Converts this string to a new character array.

Returns
  • a newly allocated character array whose length is the length of this string and whose contents are initialized to contain the character sequence represented by this string.

public String toLowerCase ()

Converts all of the characters in this String to lower case.

Returns
  • the String, converted to lowercase.
See Also

public String toString ()

This object (which is already a string!) is itself returned.

Returns
  • the string itself.

public String toUpperCase ()

Converts all of the characters in this String to upper case.

Returns
  • the String, converted to uppercase.
See Also

public String trim ()

Removes white space from both ends of this string.

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.

Returns
  • this string, with white space removed from the front and end.

public static String valueOf (boolean b)

Returns the string representation of the boolean argument.

Parameters
b a boolean.
Returns
  • if the argument is true, a string equal to "true" is returned; otherwise, a string equal to "false" is returned.

public static String valueOf (double d)

Returns the string representation of the double argument.

The representation is exactly the one returned by the Double.toString method of one argument.

Parameters
d a double.
Returns
  • a string representation of the double argument.
See Also

public static String valueOf (char c)

Returns the string representation of the char argument.

Parameters
c a char.
Returns
  • a newly allocated string of length 1 containing as its single character the argument c.

public static String valueOf (long l)

Returns the string representation of the long argument.

The representation is exactly the one returned by the Long.toString method of one argument.

Parameters
l a long.
Returns
  • a newly allocated string containing a string representation of the long argument.
See Also

public static String valueOf (char[] data, int offset, int count)

Returns the string representation of a specific subarray of the 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.

Parameters
data the character array.
offset the initial offset into the value of the String.
count the length of the value of the String.
Returns
  • a newly allocated string representing the sequence of characters contained in the subarray of the character array argument.
Throws
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 (Object obj)

Returns the string representation of the Object argument.

Parameters
obj an Object.
Returns
  • if the argument is null, then a string equal to "null"; otherwise, the value of obj.toString() is returned.
See Also

public static String valueOf (float f)

Returns the string representation of the float argument.

The representation is exactly the one returned by the Float.toString method of one argument.

Parameters
f a float.
Returns
  • a string representation of the float argument.
See Also

public static String valueOf (int i)

Returns the string representation of the int argument.

The representation is exactly the one returned by the Integer.toString method of one argument.

Parameters
i an int.
Returns
  • a newly allocated string containing a string representation of the int argument.
See Also

public static String valueOf (char[] data)

Returns the string representation of the char array argument. The contents of the character array are copied; subsequent modification of the character array does not affect the newly created string.

Parameters
data a char array.
Returns
  • a newly allocated string representing the same sequence of characters contained in the character array argument.