edu.stanford.nlp.ling.ValueLabel Maven / Gradle / Ivy
package edu.stanford.nlp.ling;
import java.io.Serializable;
/**
* A ValueLabel object acts as a Label with linguistic
* attributes. This is an abstract class, which doesn't actually store
* or return anything. It returns null to any requests. However,
* it does
* stipulate that equals() and compareTo() are defined solely with respect to
* value(); this should not be changed by subclasses.
* Other fields of a ValueLabel subclass should be regarded
* as secondary facets (it is almost impossible to override equals in
* a useful way while observing the contract for equality defined for Object,
* in particular, that equality must by symmetric).
* This class is designed to be extended.
*
* @author Christopher Manning
*/
public abstract class ValueLabel implements Label, Comparable, Serializable {
protected ValueLabel() {
}
/**
* Return the value of the label (or null if none).
* The default value returned by an ValueLabel is
* always null
*
* @return the value for the label
*/
public String value() {
return null;
}
/**
* Set the value for the label (if one is stored).
*
* @param value - the value for the label
*/
public void setValue(String value) {
}
/**
* Return a string representation of the label. This will just
* be the value() if it is non-null,
* and the empty string otherwise.
*
* @return The string representation
*/
@Override
public String toString() {
String val = value();
return (val == null) ? "" : val;
}
public void setFromString(String labelStr) {
throw new UnsupportedOperationException();
}
/**
* Equality for ValueLabels is defined in the first instance
* as equality of their String value().
* Now rewritten to correctly enforce the contract of equals in Object.
* Equality for a ValueLabel is determined simply by String
* equality of its value(). Subclasses should not redefine
* this to include other aspects of the ValueLabel, or the
* contract for equals() is broken.
*
* @param obj the object against which equality is to be checked
* @return true if this and obj are equal
*/
@Override
public boolean equals(Object obj) {
String val = value();
return (obj instanceof ValueLabel) && (val == null ? ((Label) obj).value() == null : val.equals(((Label) obj).value()));
}
/**
* Return the hashCode of the String value providing there is one.
* Otherwise, returns an arbitrary constant for the case of
* null.
*/
@Override
public int hashCode() {
String val = value();
return val == null ? 3 : val.hashCode();
}
/**
* Orders by value()'s lexicographic ordering.
*
* @param valueLabel object to compare to
* @return result (positive if this is greater than obj)
*/
public int compareTo(ValueLabel valueLabel) {
return value().compareTo(valueLabel.value());
}
/**
* Returns a factory that makes Labels of the appropriate sort.
*
* @return the LabelFactory
*/
public abstract LabelFactory labelFactory();
private static final long serialVersionUID = -1413303679077285530L;
}