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General data-binding functionality for Jackson: works on core streaming API

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package com.fasterxml.jackson.databind.node;

import java.io.IOException;

import com.fasterxml.jackson.core.*;
import com.fasterxml.jackson.databind.SerializerProvider;


/**
 * This singleton value class is used to contain explicit JSON null
 * value.
 */
public final class NullNode
    extends ValueNode
{
    // // Just need a fly-weight singleton

    public final static NullNode instance = new NullNode();

    /**
     *
     * NOTE: visibility raised to `protected` in 2.9.3 to allow custom subtypes.
     */
    protected NullNode() { }

    public static NullNode getInstance() { return instance; }

    @Override
    public JsonNodeType getNodeType() {
        return JsonNodeType.NULL;
    }

    @Override public JsonToken asToken() { return JsonToken.VALUE_NULL; }

    @Override public String asText(String defaultValue) { return defaultValue; }
    @Override public String asText() { return "null"; }

    // as with MissingNode, not considered number node; hence defaults are returned if provided
    
    /*
    public int asInt(int defaultValue);
    public long asLong(long defaultValue);
    public double asDouble(double defaultValue);
    public boolean asBoolean(boolean defaultValue);
    */
    
    @Override
    public final void serialize(JsonGenerator g, SerializerProvider provider)
        throws IOException
    {
        provider.defaultSerializeNull(g);
    }

    @Override
    public boolean equals(Object o) {
        return (o == this);
    }

    @Override
    public int hashCode() {
        return JsonNodeType.NULL.ordinal();
    }
}