String Constructors
The String class supports several constructors. To create an empty String, you call the default
constructor.
Example:
String s
= new String();
It will create an instance of String
with no characters in it.
Frequently, you will want to create strings that have initial
values.
The String class provides a variety of constructors to handle this.
To
create a String initialized by an array of characters
String(char chars[ ])
Example:
char
chars[] = { 'a', 'b', 'c' };
String s
= new String(chars);
You can specify a subrange of a character array as an
initializer using the following constructor:
Here, startIndex specifies the index at which the subrange begins, and numChars specifies the
number of characters to use.
Example:
char
chars[] = { 'a', 'b', 'c', 'd', 'e', 'f' };
String sam
= new String(chars, 2, 3);
This initializes s with the characters cde. You can construct a String
object that contains the same character sequence
as another String object using this constructor:
String(String str)
Here, str is a String object.
Example:
class
CreateString {
public
static void main(String args[]) {
char c[]
= {'J', 'a', 'v', 'a'};
String s1
= new String(c);
String s2
= new String(s1);
System.out.println(s1);
System.out.println(s2);
}
}
output:
Java
Java
s1 and s2 contain the same string.
VA RY
- Even though Java’s char type uses 16 bits to represent the Unicode character set, the typical format for strings on the Internet uses arrays of 8-bit bytes constructed from the ASCII character set.
- Because 8-bit ASCII strings are common, the String class provides constructors that initialize a string when given a byte array.
String(byte asciiChars[ ])
String(byte asciiChars[ ], int startIndex, int numChars)
- asciiChars specifies the array of bytes.
- The second form allows you to specify a subrange. In each of these constructors, the byte-to-character conversion is done by using the default character encoding of the platform.
Example:
class SubStringCons {
public
static void main(String args[]) {
byte
ascii[] = {65, 66, 67, 68, 69, 70 };
String s1
= new String(ascii);
System.out.println(s1);
String s2
= new String(ascii, 2, 3);
System.out.println(s2);
}
}
output:
ABCDEF
CDE
- Extended versions of the byte-to-string constructors are also defined in which you can specify the character encoding that determines how bytes are converted to characters.
- The contents of the array are copied whenever you create a String object from an array. If you modify the contents of the array after you have created the string, the String will be unchanged.
The length of a string is the number of characters that it
contains. To obtain this value, call the length(
) method
int length( )
The following fragment prints “3”, since there are three
characters in the string s:
char
chars[] = { 'a', 'b', 'c' };
String s
= new String(chars);
System.out.println(s.length());
