STRING CONSTRUCTOR IN JAVA

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);

 This constructor initializes s with the string “abc”.

You can specify a subrange of a character array as an initializer using the following constructor:

 String(char chars[ ], int startIndex, int numChars)

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.

 String Length

        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());