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Java™
by example!
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What is a String and how do I create one?
Internally, a String encapsulates an array of characters. The reason for this encapsulation is that the String object ensures that the string will be maintained properly. It also encapsulates a number of useful methods that can be performed on a string.
The most important thing to remember is that a String is immutable, which means that after you assigned your String object a value, it cannot change anymore during its lifetime. If you want to manipulate the characters, consider using the StringBuffer class!
There are two ways to create a String object:
- implicitely: when you use a string literal, like "Hello, world!", Java automatically creates a String object for you.
For example:
String s = "Hello, world!";
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You can use all String methods on a string literal, eg.
s = "Hello, World!".substring(7); // assigns "world!" to s
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- explicitely: when you use the new operator to instantiate a String object.
For example:
String s = new String("Hello, world!");
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This will call the String class constructor that takes another String as parameter. (remember, "Hello, world!" is represented internally as a String object!).
The String object has other constructors to create Strings as shown in the following testprogram:
public class TestProg
{
public static void main(String args[])
{
try {
String s;
StringBuffer sb = new StringBuffer("A StringBuffer");
// create a char array
char ca[] = "A character array!".toCharArray();
// create a byte array containing the default encoding ISO-Latin-1
byte ba[] = "A byte array!".getBytes();
// create a byte array containing Unicode
byte bau[] = "A Unicode byte array!".getBytes("Unicode");
// create an empty String
s = new String();
System.out.println(s); // prints out nothing
// create a String from a byte array
s = new String(ba);
System.out.println(s); // prints out "A byte array!"
// create a String from a byte array from index 2 (inclusive), take 1 byte
s = new String(ba, 2, 1);
System.out.println(s); // prints out "byte"
// create a String from a byte subarray containing Unicode
s = new String(bau, "Unicode");
System.out.println(s); // prints out "A Unicode byte array!"
// create a String from a byte subarray containing Unicode
s = new String(bau, 0, 20, "Unicode");
System.out.println(s); // prints out "A Unicode"
// create a String from a StringBuffer
s = new String(sb);
System.out.println(s); // prints out "A StringBuffer"
// create a String from a character subarray
s = new String(ca, 2, 4);
System.out.println(s); // prints out "char"
// create a String from a character array
s = new String(ca);
System.out.println(s); // prints out "A character array!"
}
catch(java.io.UnsupportedEncodingException e) {
System.out.println(e);
}
}
}
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Notice that you need to catch java.io.UnsupportedEncodingException for the methods in which you have to specify an encoding.
Further Information
Author of answer: unknown
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