Java Strings

Fundamentals

A character constant is an integer value denoted by an alphanumeric symbol enclosed in single quotes. For example, 'z' denotes the integer value of z, and '\n' denotes the newline character.

A string is a series of characters treated as a single unit, and is an object of class String. String literals or string constants (often called anonymous strings) are written as a sequence of alphanumeric symbols enclosed in double quotaion marks. For example, "Computer Graphics" is a string constant.

A StringBuffer is a dynamically resizable and modifiable string. Ordinary String objects can not be changed.

Here are some 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.

Examples of String Construction

public class string1 {
	public static void main(String args[])
	{
		// Examples of string construction
		String s1, s2, s3, s4;
		s1 = "Hello";
		s2 = new String();
		s3 = new String("World");
		show("s1",s1);
		show("s2",s2);
		show("s3",s3);
		s4 = s1;
		s1 = s1 + ", " + s3;
		show("s4",s4);
		show("s1 (concatenated)",s1);
		show("s4",s4);
	}
	public static void show(String name, String s)
	{
		System.out.println(name+": ("+ s.length() + ") " + s  );
	}
}

Run this example with: 

	java string1 > string1.txt

The output is saved in the file string1.txt: 

s1: (5) Hello
s2: (0) 
s3: (5) World
s4: (5) Hello
s1 (concatenated): (12) Hello, World
s4: (5) Hello

Note that s1 is a different string after the concatenation operation.

Retrieving characters from a String

length() returns the length of the string

charAt(int index) returns the character at a specific location, indexed from zero.

getChars(int first, int last, char array[], int offset) returns an array of characters. The first argument is the starting index from which characters are copied in the String and the second is one past the last index to be copied. array is the destination array and offset is the starting index in the destination. 

// string2.java

public class string2 {
	public static void main(String args[])
	{
		String s1;
		s1 = new String("abcdefg");
		show("s1",s1);
		System.out.println("fourth character is " + s1.charAt(3) );

		int len = s1.length();
		char array[] = new char[len];
		s1.getChars(0, len, array, 0);
		String s2 = ""; // empty string
		s2 += array[0];
		for (int i=1; i<len; i++) s2 += " " +  array[i];
		show("s2",s2);
	}
	public static void show(String name, String s)
	{
		System.out.println(name+": ("+ s.length() + ") " + s  );
	}
}

output: 

s1: (7) abcdefg
fourth character is d
s2: (13) a b c d e f g

Comparing Strings

// string3.java

public class string3 {
	public static void main(String args[])
	{
		String s1, s2, s3, s4;
		s1 = new String("abcdefgh");
		s2 = new String("abcDEFgh");
		s3 = new String("hello");
		s4 = new String("hello");
		
		show("s1.equals(s2) = " + s1.equals(s2));
		show("s1.equalsIgnoreCase(s2) = " + s1.equalsIgnoreCase(s2));
		show("s1.compareTo(s2) = " + s1.compareTo(s2) );

		show("s3.equals(s4) = " + s3.equals(s4) );
		show("(s3==s4) = " + (s3==s4) );
		show("(s3.intern()==s4.intern()) = " + (s3.intern()==s4.intern()) );

		show("s1.regionMatches(3, s2, 3, 3) = " + s1.regionMatches(3, s2, 3, 3) );
		show("s1.regionMatches(true, 3, s2, 3, 3) = " + s1.regionMatches(true, 3, s2, 3, 3) );
	}
	public static void show(String s)
	{
		System.out.println(s);
	}
}

output: 

s1.equals(s2) = false
s1.equalsIgnoreCase(s2) = true
s1.compareTo(s2) = 32
s3.equals(s4) = true
(s3==s4) = false
(s3.intern()==s4.intern()) = true
s1.regionMatches(3, s2, 3, 3) = false
s1.regionMatches(true, 3, s2, 3, 3) = true

Locating characters and substrings in Strings

public class string4 {
   public static void main( String args[] )
   {
      String letters = "abcdefghijklmabcdefghijklm";

      // test indexOf to locate a character in a string
      show( "'c' is located at index " +
			letters.indexOf( 'c' ) );

      show( "'a' is located at index " +
			letters.indexOf( 'a', 1 ) );

      show(  "'$' is located at index " +
			letters.indexOf( '$' ) );

      // test lastIndexOf to find a character in a string
      show(  "\nLast 'c' is located at index " +
			 letters.lastIndexOf( 'c' ) );

      show(  "Last 'a' is located at index " +
			 letters.lastIndexOf( 'a', 25 ) );

      show(  "Last '$' is located at index " +
			 letters.lastIndexOf( '$' ) );

      // test indexOf to locate a substring in a string
      show(  "\n\"def\" is located at index " +
			 letters.indexOf( "def" ) );

      show(  "\"def\" is located at index " +
			 letters.indexOf( "def", 7 ) );

      show(  "\"hello\" is located at index " +
			 letters.indexOf( "hello" ) );

      // test lastIndexOf to find a substring in a string
      show(  "\nLast \"def\" is located at index " +
			 letters.lastIndexOf( "def" ) );

      show(  "Last \"def\" is located at index " +
			 letters.lastIndexOf( "def", 25 ) );

      show(  "Last \"hello\" is located at index " +
			 letters.lastIndexOf( "hello" ) );
   }
   public static void show(String s)
   {
	   System.out.println(s);
   }
}

output: 

'c' is located at index 2
'a' is located at index 13
'$' is located at index -1

Last 'c' is located at index 15
Last 'a' is located at index 13
Last '$' is located at index -1

"def" is located at index 3
"def" is located at index 16
"hello" is located at index -1

Last "def" is located at index 16
Last "def" is located at index 16
Last "hello" is located at index -1

Extracting Substrings from Strings

public class SubString {
   public static void main( String args[] )
   {
      String letters = "abcdefghijklmabcdefghijklm";

      // test substring methods
      show( "Substring from index 20 to end is " +
               "\"" + letters.substring( 20 ) + "\"" );

      show( "Substring from index 0 up to 6 is " +
                "\"" + letters.substring( 0, 6 ) + "\"" );

   }

   public static void show(String s)
   {
	   System.out.println(s);
   }
}

output: 

Substring from index 20 to end is "hijklm"
Substring from index 0 up to 6 is "abcdef"

Concatenating Strings

// StringConcat.java
// This program demonstrates the String class concat method.
// Note that the concat method returns a new String object. It
// does not modify the object that invoked the concat method.

public class StringConcat {
   public static void main( String args[] )
   {
      String s1 = new String( "Happy " ),
             s2 = new String( "Birthday" );

	  show( "s1 = " + s1 );
      show( "s2 = " + s2 );

      show(  "\nResult of s1.concat( s2 ) = " +
                s1.concat( s2 ) );

      show(  "s1 after concatenation = " + s1 );

   }
   public static void show(String s)
   {
	   System.out.println(s);
   }
}

output: 

s1 = Happy 
s2 = Birthday

Result of s1.concat( s2 ) = Happy Birthday
s1 after concatenation = Happy

Miscellaneous String Methods

// StringMisc2.java
// This program demonstrates the String methods replace,
// toLowerCase, toUpperCase, trim, toString and toCharArray

public class StringMisc2 {
   public static void main( String args[] )
   {
      String s1 = new String( "hello" ),
             s2 = new String( "GOOD BYE" ),
             s3 = new String( "   spaces   " );

      show( "s1 = " + s1);
	  show( "s2 = " + s2);
	  show( "s3 = " + s3);

      // test method replace      
      show( "\nReplace 'l' with 'L' in s1: " +
                s1.replace( 'l', 'L' ) );

      // test toLowerCase and toUpperCase
      show( "\ns1.toUpperCase() = " + s1.toUpperCase() );
      show( "s2.toLowerCase() = " + s2.toLowerCase() );

      // test trim method
      show( "\ns3 after trim = \"" + s3.trim() + "\"" );

      // test toString method
      show( "\ns1 = " + s1.toString() );

      // test toCharArray method
      char charArray[] = s1.toCharArray();
	  String output = "\ns1 as a character array = ";

      for ( int i = 0; i < charArray.length; ++i )
         output += charArray[ i ];
	  show(output);

   }
   public static void show(String s)
   {
	   System.out.println(s);
   }
}

output: 

s1 = hello
s2 = GOOD BYE
s3 =    spaces   

Replace 'l' with 'L' in s1: heLLo

s1.toUpperCase() = HELLO
s2.toLowerCase() = good bye

s3 after trim = "spaces"

s1 = hello

s1 as a character array = hello

Using String method ValueOf

// StringValueOf.java
// This program demonstrates the String class valueOf methods.

public class StringValueOf {
   public static void main( String args[] )
   {
      char charArray[] = { 'a', 'b', 'c', 'd', 'e', 'f' };
      boolean b = true;
      char c = 'Z';
      int i = 7;
      long l = 10000000;
      float f = 2.5f;
      double d = 33.333;
      Object o = "hello";  // Assign to an Object reference

      show( "char array = " + String.valueOf( charArray ) );
      show( "part of char array = " +
               String.valueOf( charArray, 3, 3 ) );
      show( "boolean = " + String.valueOf( b ) );
      show( "char = " + String.valueOf( c ) );
      show( "int = " + String.valueOf( i ) );
      show( "long = " + String.valueOf( l ) );
      show( "float = " + String.valueOf( f ) );
      show( "double = " + String.valueOf( d ) );
      show( "Object = " + String.valueOf( o ) );
   }
   public static void show(String s)
   {
	   System.out.println(s);
   }
}

output: 

char array = abcdef
part of char array = def
boolean = true
char = Z
int = 7
long = 10000000
float = 2.5
double = 33.333
Object = hello

String Method intern()

// StringIntern.java
// This program demonstrates the intern method
// of the String class.

public class StringIntern {
   public static void main( String args[] )
   {
      String s1, s2, s3, s4;

      s1 = new String( "hello" );
      s2 = new String( "hello" );

      // Test strings to determine if they are the same
      // String object in memory.
      if ( s1 == s2 )
         show( "s1 and s2 are the same object in memory" );
      else
         show( "s1 and s2 are not the same object in memory" );

      // Test strings for equality of contents
      if ( s1.equals( s2 ) )
         show( "s1 and s2 are equal" );
      else
         show( "s1 and s2 are not equal" );

      // Use String intern method to get a unique copy of
      // "hello" referred to by both s3 and s4.
      s3 = s1.intern();
      s4 = s2.intern();

      // Test strings to determine if they are the same
      // String object in memory.
      if ( s3 == s4 )
         show( "s3 and s4 are the same object in memory" );
      else
         show( "s3 and s4 are not the same object in memory" );

      // Determine if s1 and s3 refer to the same object
      if ( s1 == s3 )
         show( "s1 and s3 are the same object in memory" );
      else
         show( "s1 and s3 are not the same object in memory" );

      // Determine if s2 and s4 refer to the same object
      if ( s2 == s4 )
         show( "s2 and s4 are the same object in memory" );
      else
         show( "s2 and s4 are not the same object in memory" );

      // Determine if s1 and s4 refer to the same object
      if ( s1 == s4 )
         show( "s1 and s4 are the same object in memory" );
      else
         show( "s1 and s4 are not the same object in memory" );

   }
   public static void show(String s)
   {
	   System.out.println(s);
   }
}

output: 

s1 and s2 are not the same object in memory
s1 and s2 are equal
s3 and s4 are the same object in memory
s1 and s3 are not the same object in memory
s2 and s4 are not the same object in memory
s1 and s4 are not the same object in memory

String Methods

length

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.

charAt

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.

getChars

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

getBytes

public byte[] getBytes(String enc)
                throws UnsupportedEncodingException
Convert this String into bytes according to the specified character encoding, storing the result into a new byte array.

Parameters:
enc - The name of a supported character encoding
Returns:
The resultant byte array
Throws:
UnsupportedEncodingException - If the named encoding is not supported

getBytes

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.

equals

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.

equalsIgnoreCase

public boolean equalsIgnoreCase(String anotherString)
Compares this 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:

Parameters:
anotherString - the String to compare this String against.
Returns:
true if the argument is not null and the Strings are equal, ignoring case; false otherwise.

compareTo

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.

compareTo

public int compareTo(Object o)
Compares this String to another Object. If the Object is a String, this function behaves like compareTo(String). Otherwise, it throws a ClassCastException (as Strings are comparable only to other Strings).

Specified by:
compareTo in interface Comparable
Parameters:
o - the Object to be compared.
Returns:
the value 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.
Throws:
ClassCastException - if the argument is not a String.

compareToIgnoreCase

public int compareToIgnoreCase(String str)
Compares two strings lexicographically, ignoring case considerations. This method returns an integer whose sign is that of 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.

Parameters:
str - the String to be compared.
Returns:
a negative integer, zero, or a positive integer as the the specified String is greater than, equal to, or less than this String, ignoring case considerations.

regionMatches

public boolean regionMatches(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 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:

regionMatches

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:

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.

startsWith

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.

startsWith

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.

endsWith

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.

hashCode

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.

indexOf

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.

indexOf

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.

lastIndexOf

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.

lastIndexOf

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.

indexOf

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.

indexOf

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

lastIndexOf

public int lastIndexOf(String str)
Returns the index within this string of the rightmost occurrence of the specified substring. The rightmost empty string "" is considered to occur at the index value this.length(). The returned index is the largest value k such that 
 this.startsWith(str, k)
is true.

Parameters:
str - the substring to search for.
Returns:
if the string argument occurs one or more times as a substring within this object, then the index of the first character of the last such substring is returned. If it does not occur as a substring, -1 is returned.
Throws:
NullPointerException - if str is null.

lastIndexOf

public int lastIndexOf(String str,
                       int fromIndex)
Returns the index within this string of the last occurrence of the specified substring. The returned index indicates the start of the substring, and it must be equal to or less than fromIndex. That is, the index returned is the largest value k such that: 
 this.startsWith(str, k) && (k <= fromIndex)

Parameters:
str - the substring to search for.
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.
Returns:
If the string argument occurs one or more times as a substring within this object at a starting index no greater than 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.
Throws:
NullPointerException - if str is null.

substring

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.

substring

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.

concat

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.

replace

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.

toLowerCase

public String toLowerCase(Locale locale)
Converts all of the characters in this 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

Parameters:
locale - use the case transformation rules for this locale
Returns:
the String, converted to lowercase.

toLowerCase

public String toLowerCase()
Converts all of the characters in this 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 ""

Returns:
the string, converted to lowercase.

toUpperCase

public String toUpperCase(Locale locale)
Converts all of the characters in this 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

Parameters:
locale - use the case transformation rules for this locale
Returns:
the String, converted to uppercase.

toUpperCase

public String toUpperCase()
Converts all of the characters in this 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: 

 "Fahrvergnügen".toUpperCase() returns "FAHRVERGNÜGEN"
 "Visit Ljubinje!".toUpperCase() returns "VISIT LJUBINJE!"

Returns:
the string, converted to uppercase.

trim

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.

toString

public String toString()
This object (which is already a string!) is itself returned.
Returns:
the string itself.

toCharArray

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.

valueOf

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.

valueOf

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.

valueOf

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.

copyValueOf

public static String copyValueOf(char[] data,
                                 int offset,
                                 int count)
Returns a String that is equivalent to the specified character array. It creates a new array and copies the characters into it.

Parameters:
data - the character array.
offset - initial offset of the subarray.
count - length of the subarray.
Returns:
a String that contains the characters of the specified subarray of the character array.

copyValueOf

public static String copyValueOf(char[] data)
Returns a String that is equivalent to the specified character array. It creates a new array and copies the characters into it.

Parameters:
data - the character array.
Returns:
a String that contains the characters of the character array.

valueOf

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.

valueOf

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.

valueOf

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.

valueOf

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.

valueOf

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 newly allocated string containing a string representation of the float argument.

valueOf

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 newly allocated string containing a string representation of the double argument.

intern

public String intern()
Returns a canonical representation for the string object.

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

Returns:
a string that has the same contents as this string, but is guaranteed to be from a pool of unique strings.

Maintained by John Loomis, last updated 1 June 2000