com.nginious.http.xsp.expr.NullValue.java Source code

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Here is the source code for com.nginious.http.xsp.expr.NullValue.java

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/**
 * Copyright 2012 NetDigital Sweden AB
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
*/

package com.nginious.http.xsp.expr;

import org.objectweb.asm.MethodVisitor;
import org.objectweb.asm.Opcodes;

/**
 * A value which represents <code>null</code>. A null value does not have
 * a type.
 * 
 * @author Bojan Pisler, NetDigital Sweden AB
 *
 */
public class NullValue extends Value {

    /**
     * Constructs a new null value.
     */
    public NullValue() {
        super();
    }

    /**
     * Returns this values type, {@link Type#ANY}.
     * 
     * @return this values type
     */
    protected Type getType() {
        return Type.ANY;
    }

    /**
     * Evaluates this value.
     * 
     * @return result of evaluating this value
     */
    protected Value evaluate() {
        return this;
    }

    /**
     * Evaluates this null values as an integer.
     * 
     * @return <code>0</code>
     */
    protected int getIntValue() {
        return 0;
    }

    /**
     * Evaluates this null value as a double.
     * 
     * @return <code>0.0d</code>
     */
    protected double getDoubleValue() {
        return 0.0d;
    }

    /**
     * Evaluates this null value as a string.
     * 
     * @return <code>null</code>
     */
    protected String getStringValue() {
        return null;
    }

    /**
     * Evaluates this null value as a boolean.
     * 
     * @return <code>false</code>
     */
    protected boolean getBooleanValue() {
        return false;
    }

    /**
     * Creates bytecode for this null value. The bytecode is generated using the specified method 
     * visitor. The result of the evaluation produces the specified type.
     * 
     * @param visitor the method visitor
     * @param type the type
     */
    void compile(MethodVisitor visitor, Type type) {
        if (type == Type.STRING) {
            visitor.visitInsn(Opcodes.ACONST_NULL);
        } else if (type == Type.INT) {
            visitor.visitLdcInsn(0);
        } else if (type == Type.DOUBLE) {
            visitor.visitLdcInsn(0.0d);
        }
    }
}