Creating Strings, String Buffers, and String Builders - Java Tutorial 5.0 英文版

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Creating Strings, String Buffers, and String Builders

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, a string buffer, or a string builder. The following table shows the constructors provided by the String class.

Constructors in the String Class^*

Constructor	Description
String(byte[]) String(byte[], int, int) String(byte[], int, int, String) String(byte[], String)	Creates a string whose value is set from the contents of an array of bytes. The two integer arguments, when present, set the offset and the length, respectively, of the subarray from which to take the initial values. The String argument, when present, specifies the character encoding to use to convert bytes to characters.
String(char[]) String(char[], int, int)	Creates a string whose value is set from the contents of an array of characters. The two integer arguments, when present, set the offset and the length, respectively, of the subarray from which to take the initial values.

* The String class defines other constructors not listed in this table. Those constructors have been deprecated, and/or their use is not recommended.

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 or string builder. Because the two classes have similar constructors, the following table lists only the constructors for string builders.

Constructors in the StringBuilder Class

Constructor	Description
StringBuilder()	Creates an empty string builder.
StringBuilder(CharSequence)	Constructs a string builder containing the same characters as the specified CharSequence.
StringBuilder(int)	Creates an empty string builder with the specified initial capacity.
StringBuilder(String)	Creates a string builder whose value is initialized by the specified string.

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