cdc.prefs.AbstractPreference Maven / Gradle / Ivy
package cdc.prefs;
import java.util.function.Function;
import java.util.prefs.Preferences;
/**
* Base implementation of Preference.
*
* @author Damien Carbonne
*
* @param The preference type.
*/
public abstract class AbstractPreference implements Preference {
private final Class valueClass;
private final Preferences node;
private final String key;
private final T def;
private final Function toString;
private final Function fromString;
/**
* Creates an abstract preference.
*
* If {@code toString } is {@code null}, {@link #toString} must be implemented.
* If {@code fromString } is {@code null}, {@link #fromString} must be implemented.
*
* @param valueClass The value class.
* @param node The Preferences node.
* @param key The preferences key.
* @param def The default value.
* @param toString Optional function used to convert from value type to string.
* @param fromString Optional function used to convert from string to value type.
*/
protected AbstractPreference(Class valueClass,
Preferences node,
String key,
T def,
Function toString,
Function fromString) {
this.valueClass = valueClass;
this.node = node;
this.key = key;
this.def = def;
this.toString = toString;
this.fromString = fromString;
}
/**
* Creates an abstract preference.
*
* {@link #toString} and {@link #fromString} must be implemented.
*
* @param valueClass The value class.
* @param node The Preferences node.
* @param key The preferences key.
* @param def The default value.
*/
protected AbstractPreference(Class valueClass,
Preferences node,
String key,
T def) {
this(valueClass, node, key, def, null, null);
}
/**
* Converts a value to a string using {@code toString}.
*
* If {@code value} is {@code null}, returns {@code ""}.
*
* @param value The value.
* @return The corresponding string.
* @throws IllegalStateException When {@code toString} is {@code null} and {@code value} is not {@code null}.
*/
protected String toString(T value) {
if (value == null) {
return "";
} else if (toString != null) {
return toString.apply(value);
} else {
throw new IllegalStateException();
}
}
/**
* Converts a string to a value using {@code fomString}.
*
* If {@code s} is {@code null} or empty, returns {@code null}.
*
* @param s The string.
* @return The corresponding value.
* @throws IllegalStateException When {@code fromString} is {@code null} and{@code s} is neither {@code null} or empty.
*/
protected T fromString(String s) {
if (s == null || s.isEmpty()) {
return null;
} else if (fromString != null) {
return fromString.apply(s);
} else {
throw new IllegalStateException();
}
}
@Override
public final Class getValueClass() {
return valueClass;
}
@Override
public final Preferences getNode() {
return node;
}
@Override
public final String getKey() {
return key;
}
@Override
public final T getDefaultValue() {
return def;
}
@Override
public final void put(T value) {
if (value == null) {
getNode().put(getKey(), "");
} else {
getNode().put(getKey(), toString(value));
}
}
@Override
public final T get(T def) {
final String value = getNode().get(getKey(), null);
if (value == null) {
return def;
} else {
try {
return fromString(value);
} catch (final Exception e) {
return def;
}
}
}
}