[Chapter 30] 30.17 java.util.Properties (JDK 1.0)

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| Chapter 30 The java.util Package |

## 30.17 java.util.Properties (JDK 1.0)

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This class is an extension of `Hashtable` that allows key/value pairs to be read from and written to a stream. The `Properties` class is used to implement the system properties list, which supports user customization by allowing programs to look up the value of named resources.

When you create a `Properties` object, you may specify another `Properties` object that contains default values. Keys (property names) and values are associated in a `Properties` object with the `Hashtable` method `put()`. Values are looked up with `getProperty()`--if this method does not find the key in the current `Properties` object, it looks in the default `Properties` object that was passed to the constructor method. A default value may also be specified in case the key is not found at all.

`propertyNames()` returns an enumeration of all property names (keys) stored in the `Properties` object and (recursively) also all property names stored in the default `Properties` object associated with it. `list()` prints the properties stored in a `Properties` object. It is useful for debugging. `save()` writes a `Properties` object to a stream. `load()` reads key/value pairs from a stream and stores them in a `Properties` object.

    public class Properties extends Hashtable {
        // Public Constructors
                public Properties();
                public Properties(Properties defaults);
        // Protected Instance Variables
                protected Properties defaults;
        // Public Instance Methods
                public String getProperty(String key);
                public String getProperty(String key, String defaultValue);
                public void list(PrintStream out);
            1.1public void list(PrintWriter out);
                public synchronized void load(InputStream in) throws IOException;
                public Enumeration propertyNames();
                public synchronized void save(OutputStream out, String header);
    }

### Hierarchy:

Object->Dictionary->Hashtable(Cloneable, Serializable)->Properties

### Passed To:

Properties(), System.setProperties(), Toolkit.getPrintJob()

### Returned By:

System.getProperties()

### Type Of:

Properties.defaults

java.util.Observer (JDK 1.0) |  | java.util.PropertyResourceBundle (JDK 1.1)