Java Doc for String.java in  » 6.0-JDK-Modules » j2me » java » lang » Java Source Code / Java DocumentationJava Source Code and Java Documentation

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.
version:
   12/17/01 (CLDC 1.1)
See Also:   java.lang.Object.toString
See Also:   java.lang.StringBuffer
See Also:   java.lang.StringBuffer.append(boolean)
See Also:   java.lang.StringBuffer.append(char)
See Also:   java.lang.StringBuffer.append(char[])
See Also:   java.lang.StringBuffer.append(char[]intint)
See Also:   java.lang.StringBuffer.append(int)
See Also:   java.lang.StringBuffer.append(long)
See Also:   java.lang.StringBuffer.append(java.lang.Object)
See Also:   java.lang.StringBuffer.append(java.lang.String)
since:
   JDK1.0, CLDC 1.0

If the length of the argument string is 0, then this String object is returned.

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).

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)
 

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 String.equals(Object) method, then the string from the pool is returned.

A substring of this String object is compared to a substring of the argument other.

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)
 

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'.

The offset argument is the index of the first character of the subarray.

The representation is exactly the one returned by the Integer.toString method of one argument.
Parameters:
  i - an int.

The representation is exactly the one returned by the Long.toString method of one argument.
Parameters:
  l - a long.

The representation is exactly the one returned by the Float.toString method of one argument.
Parameters:
  f - a float.

The representation is exactly the one returned by the Double.toString method of one argument.
Parameters:
  d - a double.

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)
 

 this.length()-anotherString.length()
 

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"
 

Two characters c1 and c2 are considered the same, ignoring case if at least one of the following is true:

• The two characters are the same (as compared by the == operator).
• Applying the method java.lang.Character.toUpperCase(char) to each character produces the same result.
• Applying the method java.lang.Character.toLowerCase(char) to each character produces the same result.

The first character to be copied is at index srcBegin; the last character to be copied is at index srcEnd-1 (thus the total number of characters to be copied is srcEnd-srcBegin). The characters are copied into the subarray of dst starting at index dstBegin and ending at index:

 dstbegin + (srcEnd-srcBegin) - 1
 

• srcBegin is negative.
• srcBegin is greater than srcEnd
• srcEnd is greater than the length of thisstring
• dstBegin is negative
• dstBegin+(srcEnd-srcBegin) is larger thandst.length

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

 this.charAt(k) == ch
 

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)
 

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.
Parameters:
  fromIndex - the index to start the search from. the index of the first occurrence of the character in thecharacter sequence represented by this object that is greaterthan or equal to fromIndex, or -1if the character does not occur.

 this.startsWith(str, k)
 

 this.startsWith(str, k) && (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.
Parameters:
  str - the substring to search for.
Parameters:
  fromIndex - the index to start the search from. If the string argument occurs as a substring within thisobject at a starting index no smaller thanfromIndex, then the index of the first characterof the first such substring is returned. If it does not occuras a substring starting at fromIndex or beyond,-1 is returned.
exception:
  java.lang.NullPointerException - if str isnull

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 String.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 Section 3.10.5 of the Java Language Specification a string that has the same contents as this string, but isguaranteed to be from a pool of unique strings.
since:
   CLDC 1.1

 this.charAt(k) == ch
 

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

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))
   

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)
 

this.subString(toffset).startsWith(prefix)

Examples:

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

Examples:

 "hamburger".substring(4, 8) returns "urge"
 "smiles".substring(1, 5) returns "mile"
 

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

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.
Parameters:
  offset - the initial offset into the value of theString.
Parameters:
  count - the length of the value of the String. a newly allocated string representing the sequence ofcharacters contained in the subarray of the character arrayargument.
exception:
  NullPointerException - if data isnull.
exception:
  IndexOutOfBoundsException - if offset isnegative, or count is negative, oroffset+count is larger thandata.length.

The representation is exactly the one returned by the Integer.toString method of one argument.
Parameters:
  i - an int. a newly allocated string containing a string representation ofthe int argument.
See Also:   java.lang.Integer.toString(intint)

The representation is exactly the one returned by the Long.toString method of one argument.
Parameters:
  l - a long. a newly allocated string containing a string representation ofthe long argument.
See Also:   java.lang.Long.toString(long)

The representation is exactly the one returned by the Float.toString method of one argument.
Parameters:
  f - a float. a newly allocated string containing a string representation ofthe float argument.
See Also:   java.lang.Float.toString(float)
since:
   CLDC 1.1

The representation is exactly the one returned by the Double.toString method of one argument.
Parameters:
  d - a double. a newly allocated string containing a string representation ofthe double argument.
See Also:   java.lang.Double.toString(double)
since:
   CLDC 1.1