[Java class set] _ Attribute Class: Properties notes

[Java class set] _ Attribute Class: Properties notes

Objectives of this chapter:

Measure the test taker's knowledge about the usage of the properties class.
Attributes can be saved and read to common and XML files.

A special properties class is provided in the class set to complete attribute operations.

Public class properties extends hashtable <object, Object>

Properties is a subclass of hashtable and also a subclass of map. You can use all MAP operations. However, attribute classes are generally used independently.

Set attributes:
Public object setproperty (string key, string value)

Get attributes:
Public String getproperty (string key)

Public String getproperty (string key, string defaultvalue)

Verify the preceding operations:

Import Java. util. properties; public class propertiesdemo01 {public static void main (string ARGs []) {properties pro = new properties (); // create a properties class pro. setproperty ("BJ", "Beijing"); pro. setproperty ("TJ", "Tianjing"); pro. setproperty ("NJ", "Nanjing"); system. out. println ("1. BJ attributes exist:" + pro. getproperty ("BJ"); system. out. println ("2. SC property does not exist:" + pro. getproperty ("SC"); system. out. println ("3. The SC property does not exist, and the default value is displayed at the same time:" + pro. getproperty ("SC", "no "));}}
 

The preceding attribute operations are set and read attributes. Of course, you can save the attributes in a file in the attribute operation. The following methods are provided:

Write the following attributes to the D: \ area. properties file.

Import Java. util. properties; import Java. io. file; import Java. io. fileoutputstream; import Java. io. ioexception; public class propertiesdemo02 {public static void main (string ARGs []) {properties pro = new properties (); // create a properties class pro. setproperty ("BJ", "Beijing"); pro. setproperty ("TJ", "Tianjing"); pro. setproperty ("NJ", "Nanjing"); file = new file ("D:" + file. separator + "area. properties "); // specify the file to be operated try {pro. store (New fileoutputstream (file), "area Info"); // Save the attribute to the specified file} catch (ioexception e) {e. printstacktrace ();}}}
 

Read the properties File

Public void load (inputstream instream) throws ioexception

Import Java. util. properties; import Java. io. file; import Java. io. fileinputstream; import Java. io. filenotfoundexception; import Java. io. ioexception; public class propertiesdemo03 {public static void main (string ARGs []) {properties pro = new properties (); file = new file ("D:" + file. separator + "area. properties "); // specify the file to be operated try {pro. load (New fileinputstream (File);} catch (filenotfoundexception e) {e. printstacktrace ();} catch (ioexception e) {e. printstacktrace ();} system. out. println ("1. BJ attributes exist:" + pro. getproperty ("BJ"); system. out. println ("2. Sh attributes exist:" + pro. getproperty ("sh "));}}
 

All of the above are saved in common files. In fact, you can save all the content in the XML file during the properties operation.

Import Java. util. properties; import Java. io. file; import Java. io. fileoutputstream; import Java. io. filenotfoundexception; import Java. io. ioexception; public class propertiesdemo04 {public static void main (string ARGs []) {properties pro = new properties (); // create properties object pro. setproperty ("BJ", "Beijing"); // sets the property pro. setproperty ("TJ", "Tianjin"); pro. setproperty ("NJ", "Nanjing"); file = new file ("D:" + file. separator + "area. XML "); // specify the file to be operated try {pro. storetoxml (New fileoutputstream (file), "area Info"); // Save the attribute to a common file} catch (filenotfoundexception e) {e. printstacktrace ();} catch (ioexception e) {e. printstacktrace ();}}};
 

Summary:

1. If you have a better understanding of attribute operations, you can continue to learn about the reflection mechanism and the application of the attribute class.
2. the type of the attribute must be a string, because the operation is the most convenient.
3. attributes can be saved or read to common or XML files. attributes can be expanded to any file in the specified format.