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Creating Strings and StringBuffers

A string is often created from a string literal--a series of characters enclosed in double quotes. For example, when it encounters the following string literal, the Java platform creates a String object whose value is Gobbledygook.

"Gobbledygook"

The StringsDemo program uses this technique to create the string referred to by the palindrome variable:

String palindrome = "Dot saw I was Tod";

You can also create String objects as you would any other Java object: using the new keyword and a constructor. The String class provides several constructors that allow you to provide the initial value of the string, using different sources, such as an array of characters, an array of bytes, or a string buffer.

Here's an example of creating a string from a character array:

char[] helloArray = { 'h', 'e', 'l', 'l', 'o' };
String helloString = new String(helloArray);
System.out.println(helloString);

The last line of this code snippet displays: hello.

You must always use new to create a string buffer. The StringsDemo program creates the string buffer referred to by dest, using the constructor that sets the buffer's capacity:

String palindrome = "Dot saw I was Tod";
int len = palindrome.length();
StringBuffer dest = new StringBuffer(len);

This code creates the string buffer with an initial capacity equal to the length of the string referred to by the name palindrome. This ensures only one memory allocation for dest because it's just big enough to contain the characters that will be copied to it. By initializing the string buffer's capacity to a reasonable first guess, you minimize the number of times memory must be allocated for it. This makes your code more efficient because memory allocation is a relatively expensive operation.

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