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## org.eclipse.core.runtime
Class Preferences

    java.lang.Object
      org.eclipse.core.runtime.Preferences

public class Preferences
extends Object

A table of preference settings, mapping named properties to values. Property names are non-empty strings; property values can be either booleans, non-null strings, or values of one of the primitive number types. The table consists of two, sparse, layers: the lower layer holds default values for properties, and the upper layer holds explicitly set values for properties. Normal retrieval looks for an explicitly set value for the given property in the upper layer; if there is nothing for that property in the upper layer, it next looks for a default value for the given property in the lower layer; if there is nothing for that property in the lower layer, it returns a standard default-default value. The default-default values for the primitive types are as follows:

- `boolean` = `false`
- `double` = `0.0`
- `float` = `0.0f`
- `int` = `0`
- `long` = `0L`
- `String` = `""` (the empty string)

Internally, all properties values (in both layers) are stored as strings. Standard conversions to and from numeric and boolean types are performed on demand.

The typical usage is to establish the defaults for all known properties and then restore previously stored values for properties whose values were explicitly set. The existing settings can be changed and new properties can be set (`setValue`). If the values specified is the same as the default value, the explicit setting is deleted from the top layer. It is also possible to reset a property value back to the default value using `setToDefault`. After the properties have been modified, the properties with explicit settings are written to disk. The default values are never saved. This two-tiered approach to saving and restoring property setting minimizes the number of properties that need to be persisted; indeed, the normal starting state does not require storing any properties at all. It also makes it easy to use different default settings in different environments while maintaining just those property settings the user has adjusted.

A property change event is reported whenever a property's value actually changes (either through `setValue`, `setToDefault`). Note, however, that manipulating default values (with `setDefault`) does not cause any events to be reported.

Clients may instantiate this class. This class was not designed to be subclassed.

The implementation is based on a pair of internal `java.util.Properties` objects, one holding explicitly set values (set using `setValue`), the other holding the default values (set using `setDefaultValue`). The `load` and `store` methods persist the non-default property values to streams (the default values are not saved).

If a client sets a default value to be equivalent to the default-default for that type, the value is still known to the preference store as having a default value. That is, the name will still be returned in the result of the `defaultPropertyNames` and `contains` methods.

Since:
  2.0

Nested Class Summary
`static interface` | `Preferences.IPropertyChangeListener` Listener for property changes.
`static class` | `Preferences.PropertyChangeEvent` An event object describing a change to a named property.

Field Summary
`static boolean` | `BOOLEAN_DEFAULT_DEFAULT` The default-default value for boolean properties (`false`).
`protected boolean` | `dirty` Indicates whether a value has been changed by `setToDefault` or `setValue`; initially `false`.
`static double` | `DOUBLE_DEFAULT_DEFAULT` The default-default value for double properties (`0.0`).
`protected static String` | `FALSE` The string representation used for `false` (`"false"`).
`static float` | `FLOAT_DEFAULT_DEFAULT` The default-default value for float properties (`0.0f`).
`static int` | `INT_DEFAULT_DEFAULT` The default-default value for int properties (`0`).
`protected org.eclipse.core.internal.runtime.ListenerList` | `listeners` List of registered listeners (element type: `IPropertyChangeListener`).
`static long` | `LONG_DEFAULT_DEFAULT` The default-default value for long properties (`0L`).
`static String` | `STRING_DEFAULT_DEFAULT` The default-default value for String properties (`""`).
`protected static String` | `TRUE` The string representation used for `true` (`"true"`).

Constructor Summary
`Preferences()` Creates an empty preference table.

Method Summary
`void` | `addPropertyChangeListener(Preferences.IPropertyChangeListener listener)` Adds a property change listener to this preference object.
`boolean` | `contains(String name)` Returns whether the given property is known to this preference object, either by having an explicit setting or by having a default setting.
`String[]` | `defaultPropertyNames()` Returns a list of all properties known to this preference object which have an explicit default value set.
`static void` | `exportPreferences(IPath path)` Exports all non-default-valued preferences for all installed plugins to the provided file.
`protected void` | `firePropertyChangeEvent(String name, Object oldValue, Object newValue)` Fires a property change event corresponding to a change to the current value of the property with the given name.
`boolean` | `getBoolean(String name)` Returns the current value of the boolean-valued property with the given name.
`boolean` | `getDefaultBoolean(String name)` Returns the default value for the boolean-valued property with the given name.
`double` | `getDefaultDouble(String name)` Returns the default value for the double-valued property with the given name.
`float` | `getDefaultFloat(String name)` Returns the default value for the float-valued property with the given name.
`int` | `getDefaultInt(String name)` Returns the default value for the integer-valued property with the given name.
`long` | `getDefaultLong(String name)` Returns the default value for the long-valued property with the given name.
`String` | `getDefaultString(String name)` Returns the default value for the string-valued property with the given name.
`double` | `getDouble(String name)` Returns the current value of the double-valued property with the given name.
`float` | `getFloat(String name)` Returns the current value of the float-valued property with the given name.
`int` | `getInt(String name)` Returns the current value of the integer-valued property with the given name.
`long` | `getLong(String name)` Returns the current value of the long-valued property with the given name.
`String` | `getString(String name)` Returns the current value of the string-valued property with the given name.
`static void` | `importPreferences(IPath path)` Loads the plugin preferences from the given file, and replaces all non-default-valued preferences for all plugins with the values from this file.
`boolean` | `isDefault(String name)` Returns whether the property with the given name has the default value in virtue of having no explicitly set value.
`void` | `load(InputStream in)` Loads the non-default-valued properties for this preference object from the given input stream using `java.util.Properties.load(InputStream)`.
`boolean` | `needsSaving()` Returns whether the current values in this preference object require saving.
`String[]` | `propertyNames()` Returns a list of all properties known to this preference object which have current values other than their default value.
`void` | `removePropertyChangeListener(Preferences.IPropertyChangeListener listener)` Removes the given listener from this preference object.
`void` | `setDefault(String name, boolean value)` Sets the default value for the boolean-valued property with the given name.
`void` | `setDefault(String name, double value)` Sets the default value for the double-valued property with the given name.
`void` | `setDefault(String name, float value)` Sets the default value for the float-valued property with the given name.
`void` | `setDefault(String name, int value)` Sets the default value for the integer-valued property with the given name.
`void` | `setDefault(String name, long value)` Sets the default value for the long-valued property with the given name.
`void` | `setDefault(String name, String value)` Sets the default value for the string-valued property with the given name.
`void` | `setToDefault(String name)` Sets the current value of the property with the given name back to its default value.
`void` | `setValue(String name, boolean value)` Sets the current value of the boolean-valued property with the given name.
`void` | `setValue(String name, double value)` Sets the current value of the double-valued property with the given name.
`void` | `setValue(String name, float value)` Sets the current value of the float-valued property with the given name.
`void` | `setValue(String name, int value)` Sets the current value of the integer-valued property with the given name.
`void` | `setValue(String name, long value)` Sets the current value of the long-valued property with the given name.
`void` | `setValue(String name, String value)` Sets the current value of the string-valued property with the given name.
`void` | `store(OutputStream out, String header)` Saves the non-default-valued properties known to this preference object to the given output stream using `Properties.store(OutputStream,String)`.
`static IStatus` | `validatePreferenceVersions(IPath file)` Validates that the preference versions in the given file match the versions of the currently installed plugins.

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Field Detail

### BOOLEAN_DEFAULT_DEFAULT

    public static final boolean BOOLEAN_DEFAULT_DEFAULT

  The default-default value for boolean properties (`false`).

  See Also:
    Constant Field Values

### DOUBLE_DEFAULT_DEFAULT

    public static final double DOUBLE_DEFAULT_DEFAULT

  The default-default value for double properties (`0.0`).

  See Also:
    Constant Field Values

### FLOAT_DEFAULT_DEFAULT

    public static final float FLOAT_DEFAULT_DEFAULT

  The default-default value for float properties (`0.0f`).

  See Also:
    Constant Field Values

### INT_DEFAULT_DEFAULT

    public static final int INT_DEFAULT_DEFAULT

  The default-default value for int properties (`0`).

  See Also:
    Constant Field Values

### LONG_DEFAULT_DEFAULT

    public static final long LONG_DEFAULT_DEFAULT

  The default-default value for long properties (`0L`).

  See Also:
    Constant Field Values

### STRING_DEFAULT_DEFAULT

    public static final String STRING_DEFAULT_DEFAULT

  The default-default value for String properties (`""`).

  See Also:
    Constant Field Values

### TRUE

    protected static final String TRUE

  The string representation used for `true` (`"true"`).

  See Also:
    Constant Field Values

### FALSE

    protected static final String FALSE

  The string representation used for `false` (`"false"`).

  See Also:
    Constant Field Values

### listeners

    protected org.eclipse.core.internal.runtime.ListenerList listeners

  List of registered listeners (element type: `IPropertyChangeListener`). These listeners are to be informed when the current value of a property changes.

### dirty

    protected boolean dirty

  Indicates whether a value has been changed by `setToDefault` or `setValue`; initially `false`.

Constructor Detail

### Preferences

    public Preferences()

  Creates an empty preference table.

  Use the methods `load(InputStream)` and `store(InputStream)` to load and store these preferences.

See Also:
  `load(InputStream)`, `store(OutputStream, String)`

Method Detail

### exportPreferences

    public static void exportPreferences(IPath path)
                                  throws CoreException

  Exports all non-default-valued preferences for all installed plugins to the provided file. If a file already exists at the given location, it will be deleted. If there are no preferences to export, no file will be written.

  The file that is written can be read later using the importPreferences method.

  Parameters:
    `path` - The absolute filesystem path of the file to export preferences to.
  Throws:
    `CoreException` - if this method fails. Reasons include:
    - The file could not be written.
  See Also:
    `importPreferences(IPath)`, `validatePreferenceVersions(IPath)`

### importPreferences

    public static void importPreferences(IPath path)
                                  throws CoreException

  Loads the plugin preferences from the given file, and replaces all non-default-valued preferences for all plugins with the values from this file.

  If the file contains preferences for plug-ins that don't exist in the current install, they are ignored. This method does not validate if the plug-in versions in the preference file match the currently installed plug-ins. Clients should first call validatePreferenceVersions on the file to ensure that the versions are compatible.

  The file must have been written by the exportPreferences method.

  Parameters:
    `path` - The absolute filesystem path of the file to import preferences from.
  Throws:
    `CoreException` - if this method fails. Reasons include:
    - The file does not exist.
    - The file could not be read.
  See Also:
    `exportPreferences(IPath)`, `validatePreferenceVersions(IPath)`

### validatePreferenceVersions

    public static IStatus validatePreferenceVersions(IPath file)

  Validates that the preference versions in the given file match the versions of the currently installed plugins. Returns an OK status if all preferences match the currently installed plugins, otherwise a MultiStatus describing what plugins have preferences that don't match.

  If the returned status has a `IStatus.WARNING` severity, it means that some preferences may not be applicable but for the most part they will be compatible. If the returned status has a `IStatus.ERROR` severity, it means that the preferences will probably not be compatible.

  If the file contains preferences for plug-ins that don't exist in the current install, they are ignored.

  The file must have been written by the exportPreferences method.

  Parameters:
    `file` - The absolute filesystem path of the preference file to validate.
  See Also:
    `exportPreferences(IPath)`, `importPreferences(IPath)`

### addPropertyChangeListener

    public void addPropertyChangeListener(Preferences.IPropertyChangeListener listener)

  Adds a property change listener to this preference object. Has no affect if the identical listener is already registered.

  Parameters:
    `listener` - a property change listener

### removePropertyChangeListener

    public void removePropertyChangeListener(Preferences.IPropertyChangeListener listener)

  Removes the given listener from this preference object. Has no affect if the listener is not registered.

  Parameters:
    `listener` - a property change listener

### contains

    public boolean contains(String name)

  Returns whether the given property is known to this preference object, either by having an explicit setting or by having a default setting. Returns `false` if the given name is `null`.

  Parameters:
    `name` - the name of the property, or `null`
  Returns:
    `true` if either a current value or a default value is known for the named property, and `false`otherwise

### firePropertyChangeEvent

    protected void firePropertyChangeEvent(String name,
                                           Object oldValue,
                                           Object newValue)

  Fires a property change event corresponding to a change to the current value of the property with the given name.

  Parameters:
    `name` - the name of the property, to be used as the property in the event object
    `oldValue` - the old value, or `null` if not known or not relevant
    `newValue` - the new value, or `null` if not known or not relevant

### getBoolean

    public boolean getBoolean(String name)

  Returns the current value of the boolean-valued property with the given name. Returns the default-default value (`false`) if there is no property with the given name, or if the current value cannot be treated as a boolean. The given name must not be `null`.

  Parameters:
    `name` - the name of the property
  Returns:
    the boolean-valued property

### setValue

    public void setValue(String name,
                         boolean value)

  Sets the current value of the boolean-valued property with the given name. The given name must not be `null`.

  A property change event is reported if the current value of the property actually changes from its previous value. In the event object, the property name is the name of the property, and the old and new values are wrapped as objects.

  If the given value is the same as the corresponding default value for the given property, the explicit setting is deleted. Note that the recommended way of re-initializing a property to its default value is to call `setToDefault`.

  Parameters:
    `name` - the name of the property
    `value` - the new current value of the property

### getDefaultBoolean

    public boolean getDefaultBoolean(String name)

  Returns the default value for the boolean-valued property with the given name. Returns the default-default value (`false`) if there is no default property with the given name, or if the default value cannot be treated as a boolean. The given name must not be `null`.

  Parameters:
    `name` - the name of the property
  Returns:
    the default value of the named property

### setDefault

    public void setDefault(String name,
                           boolean value)

  Sets the default value for the boolean-valued property with the given name. The given name must not be `null`.

  Note that the current value of the property is affected if the property's current value was its old default value, in which case it changes to the new default value. If the property's current is different from its old default value, its current value is unaffected. No property change events are reported by changing default values.

  Parameters:
    `name` - the name of the property
    `value` - the new default value for the property

### getDouble

    public double getDouble(String name)

  Returns the current value of the double-valued property with the given name. Returns the default-default value (`0.0`) if there is no property with the given name, or if the current value cannot be treated as a double. The given name must not be `null`.

  Parameters:
    `name` - the name of the property
  Returns:
    the double-valued property

### setValue

    public void setValue(String name,
                         double value)

  Sets the current value of the double-valued property with the given name. The given name must not be `null`.

  A property change event is reported if the current value of the property actually changes from its previous value. In the event object, the property name is the name of the property, and the old and new values are wrapped as objects.

  If the given value is the same as the corresponding default value for the given property, the explicit setting is deleted. Note that the recommended way of re-initializing a property to its default value is to call `setToDefault`.

  Parameters:
    `name` - the name of the property
    `value` - the new current value of the property; must be a number (not a NaN)

### getDefaultDouble

    public double getDefaultDouble(String name)

  Returns the default value for the double-valued property with the given name. Returns the default-default value (`0.0`) if there is no default property with the given name, or if the default value cannot be treated as a double. The given name must not be `null`.

  Parameters:
    `name` - the name of the property
  Returns:
    the default value of the named property

### setDefault

    public void setDefault(String name,
                           double value)

  Sets the default value for the double-valued property with the given name. The given name must not be `null`.

  Note that the current value of the property is affected if the property's current value was its old default value, in which case it changes to the new default value. If the property's current is different from its old default value, its current value is unaffected. No property change events are reported by changing default values.

  Parameters:
    `name` - the name of the property
    `value` - the new default value for the property; must be a number (not a NaN)

### getFloat

    public float getFloat(String name)

  Returns the current value of the float-valued property with the given name. Returns the default-default value (`0.0f`) if there is no property with the given name, or if the current value cannot be treated as a float. The given name must not be `null`.

  Parameters:
    `name` - the name of the property
  Returns:
    the float-valued property

### setValue

    public void setValue(String name,
                         float value)

  Sets the current value of the float-valued property with the given name. The given name must not be `null`.

  A property change event is reported if the current value of the property actually changes from its previous value. In the event object, the property name is the name of the property, and the old and new values are wrapped as objects.

  If the given value is the same as the corresponding default value for the given property, the explicit setting is deleted. Note that the recommended way of re-initializing a property to its default value is to call `setToDefault`.

  Parameters:
    `name` - the name of the property
    `value` - the new current value of the property; must be a number (not a NaN)

### getDefaultFloat

    public float getDefaultFloat(String name)

  Returns the default value for the float-valued property with the given name. Returns the default-default value (`0.0f`) if there is no default property with the given name, or if the default value cannot be treated as a float. The given name must not be `null`.

  Parameters:
    `name` - the name of the property
  Returns:
    the default value of the named property

### setDefault

    public void setDefault(String name,
                           float value)

  Sets the default value for the float-valued property with the given name. The given name must not be `null`.

  Note that the current value of the property is affected if the property's current value was its old default value, in which case it changes to the new default value. If the property's current is different from its old default value, its current value is unaffected. No property change events are reported by changing default values.

  Parameters:
    `name` - the name of the property
    `value` - the new default value for the property; must be a number (not a NaN)

### getInt

    public int getInt(String name)

  Returns the current value of the integer-valued property with the given name. Returns the default-default value (`0`) if there is no property with the given name, or if the current value cannot be treated as an integter. The given name must not be `null`.

  Parameters:
    `name` - the name of the property
  Returns:
    the int-valued property

### setValue

    public void setValue(String name,
                         int value)

  Sets the current value of the integer-valued property with the given name. The given name must not be `null`.

  A property change event is reported if the current value of the property actually changes from its previous value. In the event object, the property name is the name of the property, and the old and new values are wrapped as objects.

  If the given value is the same as the corresponding default value for the given property, the explicit setting is deleted. Note that the recommended way of re-initializing a property to its default value is to call `setToDefault`.

  Parameters:
    `name` - the name of the property
    `value` - the new current value of the property

### getDefaultInt

    public int getDefaultInt(String name)

  Returns the default value for the integer-valued property with the given name. Returns the default-default value (`0`) if there is no default property with the given name, or if the default value cannot be treated as an integer. The given name must not be `null`.

  Parameters:
    `name` - the name of the property
  Returns:
    the default value of the named property

### setDefault

    public void setDefault(String name,
                           int value)

  Sets the default value for the integer-valued property with the given name. The given name must not be `null`.

  Note that the current value of the property is affected if the property's current value was its old default value, in which case it changes to the new default value. If the property's current is different from its old default value, its current value is unaffected. No property change events are reported by changing default values.

  Parameters:
    `name` - the name of the property
    `value` - the new default value for the property

### getLong

    public long getLong(String name)

  Returns the current value of the long-valued property with the given name. Returns the default-default value (`0L`) if there is no property with the given name, or if the current value cannot be treated as a long. The given name must not be `null`.

  Parameters:
    `name` - the name of the property
  Returns:
    the long-valued property

### setValue

    public void setValue(String name,
                         long value)

  Sets the current value of the long-valued property with the given name. The given name must not be `null`.

  A property change event is reported if the current value of the property actually changes from its previous value. In the event object, the property name is the name of the property, and the old and new values are wrapped as objects.

  If the given value is the same as the corresponding default value for the given property, the explicit setting is deleted. Note that the recommended way of re-initializing a property to its default value is to call `setToDefault`.

  Parameters:
    `name` - the name of the property
    `value` - the new current value of the property

### getDefaultLong

    public long getDefaultLong(String name)

  Returns the default value for the long-valued property with the given name. Returns the default-default value (`0L`) if there is no default property with the given name, or if the default value cannot be treated as a long. The given name must not be `null`.

  Parameters:
    `name` - the name of the property
  Returns:
    the default value of the named property

### setDefault

    public void setDefault(String name,
                           long value)

  Sets the default value for the long-valued property with the given name. The given name must not be `null`.

  Note that the current value of the property is affected if the property's current value was its old default value, in which case it changes to the new default value. If the property's current is different from its old default value, its current value is unaffected. No property change events are reported by changing default values.

  Parameters:
    `name` - the name of the property
    `value` - the new default value for the property

### getString

    public String getString(String name)

  Returns the current value of the string-valued property with the given name. Returns the default-default value (the empty string `""`) if there is no property with the given name. The given name must not be `null`.

  Parameters:
    `name` - the name of the property
  Returns:
    the string-valued property

### setValue

    public void setValue(String name,
                         String value)

  Sets the current value of the string-valued property with the given name. The given name must not be `null`.

  A property change event is reported if the current value of the property actually changes from its previous value. In the event object, the property name is the name of the property, and the old and new values are wrapped as objects.

  If the given value is the same as the corresponding default value for the given property, the explicit setting is deleted. Note that the recommended way of re-initializing a property to its default value is to call `setToDefault`.

  Parameters:
    `name` - the name of the property
    `value` - the new current value of the property

### getDefaultString

    public String getDefaultString(String name)

  Returns the default value for the string-valued property with the given name. Returns the default-default value (the empty string `""`) is no default property with the given name, or if the default value cannot be treated as a string. The given name must not be `null`.

  Parameters:
    `name` - the name of the property
  Returns:
    the default value of the named property

### setDefault

    public void setDefault(String name,
                           String value)

  Sets the default value for the string-valued property with the given name. The given name must not be `null`.

  Note that the current value of the property is affected if the property's current value was its old default value, in which case it changes to the new default value. If the property's current is different from its old default value, its current value is unaffected. No property change events are reported by changing default values.

  Parameters:
    `name` - the name of the property
    `value` - the new default value for the property

### isDefault

    public boolean isDefault(String name)

  Returns whether the property with the given name has the default value in virtue of having no explicitly set value. Returns `false` if the given name is `null`.

  Parameters:
    `name` - the name of the property, or `null`
  Returns:
    `true` if the property has no explicitly set value, and `false` otherwise (including the case where the property is unknown to this object)

### setToDefault

    public void setToDefault(String name)

  Sets the current value of the property with the given name back to its default value. Has no effect if the property does not have its own current value. The given name must not be `null`.

  Note that the recommended way of re-initializing a property to the appropriate default value is to call `setToDefault`. This is implemented by removing the named value from the object, thereby exposing the default value.

  A property change event is always reported. In the event object, the property name is the name of the property, and the old and new values are either strings, or `null` indicating the default-default value.

  Parameters:
    `name` - the name of the property

### propertyNames

    public String[] propertyNames()

  Returns a list of all properties known to this preference object which have current values other than their default value.

  Returns:
    an array of property names

### defaultPropertyNames

    public String[] defaultPropertyNames()

  Returns a list of all properties known to this preference object which have an explicit default value set.

  Returns:
    an array of property names

### needsSaving

    public boolean needsSaving()

  Returns whether the current values in this preference object require saving.

  Returns:
    `true` if at least one of the properties known to this preference object has a current value different from its default value, and `false` otherwise

### store

    public void store(OutputStream out,
                      String header)
               throws IOException

  Saves the non-default-valued properties known to this preference object to the given output stream using `Properties.store(OutputStream,String)`.

  Note that the output is unconditionally written, even when `needsSaving` is `false`.

  Parameters:
    `out` - the output stream
    `header` - a comment to be included in the output, or `null` if none
  Throws:
    `IOException` - if there is a problem saving this preference object
  See Also:
    `Properties.store(OutputStream,String)`

### load

    public void load(InputStream in)
              throws IOException

  Loads the non-default-valued properties for this preference object from the given input stream using `java.util.Properties.load(InputStream)`. Default property values are not affected.

  Parameters:
    `in` - the input stream
  Throws:
    `IOException` - if there is a problem loading this preference object
  See Also:
    `Properties.load(InputStream)`

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