Java String Creation

In this chapter you will learn:

How to create String object with String constructors
How to create a string from byte array
How to create a string from part of a byte array
How to create String from char array
How to create String from part of a char array
How to create a String from another string

String Constructor

The String class supports several constructors.

String() from empty string
String(byte[] bytes) from byte array using default charset.
String(byte[] bytes, Charset charset) from the bytes using the specified charset.
String(byte[] bytes, int offset, int length) decoding the subarray of bytes using the platform's default charset.
String(byte[] bytes, int offset, int length, Charset charset) decoding the specified subarray of bytes using the specified charset.
String(byte[] bytes, int offset, int length, String charsetName) decoding the subarray of bytes using the specified charset.
String(byte[] bytes, String charsetName) decoding the array of bytes using the specified charset.
String(char[] value) from the character array argument.
String(char[] value, int offset, int count) from a subarray of char array argument.
String(int[] codePoints, int offset, int count) from a subarray of the Unicode code point array argument.
String(String original) creates a copy of the argument string.
String(StringBuffer buffer) from the string buffer argument.
String(StringBuilder builder) from the string builder argument.

To create an empty String, you call the default constructor. String s = new String(); will create an instance of String with no characters in it.

public class Main {
  public static void main(String args[]) {
    char charArray[] = { 'b', 'i', 'r', 't', 'h', ' ', 
                         'd', 'a', 'y' };
    String s = new String("hello");
/*from ja va2 s.  c  o  m*/
    // use String constructors
    String s1 = new String();
    String s2 = new String(s);
    String s3 = new String(charArray);
    String s4 = new String(charArray, 6, 3);

    System.out.printf("s1 = %s\ns2 = %s\ns3 = %s\ns4 = %s\n", 
                     s1, s2, s3, s4);
  }
}

The output:

Create a string from byte array

new String(byte[] bytes) initializes a string with given a byte array.

public class Main {
  public static void main(String args[]) {
    byte ascii[] = { 65, 66, 67, 68, 69, 70 };
/* j  ava  2  s  .  co m*/
    String s1 = new String(ascii);
    System.out.println(s1);

    String s2 = new String(ascii, 2, 3);
    System.out.println(s2);
  }
}

The output:

Create a string from part of a byte array

The following code creates a string from sub byte array with new String(byte[] bytes, int offset, int length).

public class Main {
  public static void main(String args[]) {
    byte ascii[] = { 65, 66, 67, 68, 69, 70 };
/* j  av a2s  .  c  o m*/
    String s1 = new String(ascii);
    System.out.println(s1);

    String s2 = new String(ascii, 2, 3);
    System.out.println(s2);
  }
}

Create a string from char array

To create a String initialized by an array of characters: new String(char[] value)

public class Main {
  public static void main(String args[]) {
    char charArray[] = { 'b', 'i', 'r', 't', 'h', ' ', 'd', 'a', 'y' };
    String s = new String("hello");
/* j  av a 2 s . co m*/
    // use String constructors
    String s1 = new String();
    String s2 = new String(s);
    String s3 = new String(charArray);
    String s4 = new String(charArray, 6, 3);

    System.out.printf("s1 = %s\ns2 = %s\ns3 = %s\ns4 = %s\n", s1, s2, s3, s4);
  }
}

Create String from part of a char array

Creating string from part of a char array with new String(char[] value, int offset, int count).

public class Main {
  public static void main(String args[]) {
    char charArray[] = { 'b', 'i', 'r', 't', 'h', ' ', 'd', 'a', 'y' };
    String s = new String("hello");
//  ja v  a  2 s . c  o  m
    // use String constructors
    String s1 = new String();
    String s2 = new String(s);
    String s3 = new String(charArray);
    String s4 = new String(charArray, 6, 3);

    System.out.printf("s1 = %s\ns2 = %s\ns3 = %s\ns4 = %s\n", s1, s2, s3, s4);
  }
}

Create a String from another string

Construct a String object that contains the same character sequence as another String object using this constructor:new String(String original)

public class Main {
  public static void main(String args[]) {
    char charArray[] = { 'b', 'i', 'r', 't', 'h', ' ', 'd', 'a', 'y' };
    String s = new String("hello");
/*from j a  v a  2 s.c  om*/
    // use String constructors
    String s1 = new String();
    String s2 = new String(s);
    String s3 = new String(charArray);
    String s4 = new String(charArray, 6, 3);

    System.out.printf("s1 = %s\ns2 = %s\ns3 = %s\ns4 = %s\n", s1, s2, s3, s4);
  }
}