AbstractFunction.java

package org.geotools.tutorial.function;

import java.util.Collections;
import java.util.List;

import org.geotools.util.Converters;
import org.opengis.filter.capability.FunctionName;
import org.opengis.filter.expression.Expression;
import org.opengis.filter.expression.ExpressionVisitor;
import org.opengis.filter.expression.Function;
import org.opengis.filter.expression.Literal;

public abstract class AbstractFunction implements Function {
    protected final FunctionName name;
    protected final List<Expression> params;
    protected final Literal fallback;
    
    protected AbstractFunction(FunctionName name, List<Expression> args, Literal fallback) {
        this.name = name;
        this.params = args;
        this.fallback = fallback;
    }
    public abstract Object evaluate(Object object);
    public <T> T evaluate(Object object, Class<T> context) {
        Object value = evaluate(object);
        return Converters.convert(value, context);
    }
    public Object accept(ExpressionVisitor visitor, Object extraData) {
        return visitor.visit(this, extraData);
    }
    public String getName() {
        return name.getName();
    }
    public FunctionName getFunctionName() {
        return name;
    }
    public List<Expression> getParameters() {
        return Collections.unmodifiableList(params);
    }
    public Literal getFallbackValue() {
        return fallback;
    }
    // helper methods
    <T> T eval( Object feature, int index, Class<T> type ){
        Expression expr = params.get(index);
        Object value = expr.evaluate( feature, type );        
        return type.cast(value);
    }
}