Implementation:Apache Paimon DataTypeDefaultVisitor

Knowledge Sources	Apache_Paimon
Domains	Type System, Design Patterns
Last Updated	2026-02-08 00:00 GMT

Overview

DataTypeDefaultVisitor is an abstract implementation of DataTypeVisitor that redirects all visit calls to a single default method, simplifying visitor implementations.

Description

DataTypeDefaultVisitor is an abstract generic class that implements the DataTypeVisitor interface, providing a convenient base for creating type visitors that handle most types uniformly with a default behavior. Rather than requiring implementations to override all 18+ visit methods for each data type (CharType, VarCharType, BooleanType, etc.), this class redirects all of them to a single abstract defaultMethod(DataType), significantly reducing boilerplate code.

This design pattern is particularly useful when you need to process most types in the same way but only specialize handling for a few specific types. Subclasses can override specific visit methods for types requiring special treatment while letting the rest fall through to the default behavior. For example, a visitor extracting numeric properties might only override visit methods for DecimalType, TimeType, and TimestampType, while all other types return a default value.

The class has been available since Paimon version 0.4.0 and is marked with the @Public annotation, indicating its stability as part of the public API. It is parameterized with type R, which represents the return type of the visitor operations, allowing for flexible result types such as integers for size calculations, strings for formatting, or custom objects for complex transformations.

Usage

Use DataTypeDefaultVisitor when implementing custom type processing logic where most types share common behavior and only a subset requires specialized handling. It is ideal for implementing property extractors, type converters, or validation logic where exceptions to the rule are minimal.

Code Reference

Source Location

• Repository: Apache_Paimon
• File: paimon-api/src/main/java/org/apache/paimon/types/DataTypeDefaultVisitor.java

Signature

@Public
public abstract class DataTypeDefaultVisitor<R> implements DataTypeVisitor<R> {

    @Override
    public R visit(CharType charType)

    @Override
    public R visit(VarCharType varCharType)

    @Override
    public R visit(BooleanType booleanType)

    @Override
    public R visit(BinaryType binaryType)

    @Override
    public R visit(VarBinaryType varBinaryType)

    @Override
    public R visit(DecimalType decimalType)

    @Override
    public R visit(TinyIntType tinyIntType)

    @Override
    public R visit(SmallIntType smallIntType)

    @Override
    public R visit(IntType intType)

    @Override
    public R visit(BigIntType bigIntType)

    @Override
    public R visit(FloatType floatType)

    @Override
    public R visit(DoubleType doubleType)

    @Override
    public R visit(DateType dateType)

    @Override
    public R visit(TimeType timeType)

    @Override
    public R visit(TimestampType timestampType)

    @Override
    public R visit(LocalZonedTimestampType localZonedTimestampType)

    @Override
    public R visit(VariantType variantType)

    @Override
    public R visit(BlobType blobType)

    @Override
    public R visit(ArrayType arrayType)

    @Override
    public R visit(VectorType vectorType)

    @Override
    public R visit(MultisetType multisetType)

    @Override
    public R visit(MapType mapType)

    @Override
    public R visit(RowType rowType)

    protected abstract R defaultMethod(DataType dataType)
}

Import

import org.apache.paimon.types.DataTypeDefaultVisitor;

I/O Contract

Inputs

Name	Type	Required	Description
dataType	DataType	Yes	Any data type to be visited (passed to defaultMethod)

Outputs

Name	Type	Description
Result	R (generic)	The result of processing the data type, type determined by implementation

Usage Examples

// Example 1: Return default size for all types except arrays
class SizeCalculator extends DataTypeDefaultVisitor<Integer> {
    @Override
    public Integer visit(ArrayType arrayType) {
        // Special handling for arrays
        return arrayType.getElementType().accept(this) * 10;
    }

    @Override
    protected Integer defaultMethod(DataType dataType) {
        return dataType.defaultSize();
    }
}

// Example 2: Check if type is a temporal type
class TemporalChecker extends DataTypeDefaultVisitor<Boolean> {
    @Override
    public Boolean visit(DateType dateType) {
        return true;
    }

    @Override
    public Boolean visit(TimeType timeType) {
        return true;
    }

    @Override
    public Boolean visit(TimestampType timestampType) {
        return true;
    }

    @Override
    protected Boolean defaultMethod(DataType dataType) {
        return false;
    }
}

// Example 3: Extract precision, return empty if not applicable
class PrecisionExtractor extends DataTypeDefaultVisitor<OptionalInt> {
    @Override
    public OptionalInt visit(DecimalType decimalType) {
        return OptionalInt.of(decimalType.getPrecision());
    }

    @Override
    public OptionalInt visit(TimestampType timestampType) {
        return OptionalInt.of(timestampType.getPrecision());
    }

    @Override
    protected OptionalInt defaultMethod(DataType dataType) {
        return OptionalInt.empty();
    }
}

// Using the visitors
DataType intType = DataTypes.INT();
DataType arrayType = DataTypes.ARRAY(DataTypes.STRING());
DataType timestampType = DataTypes.TIMESTAMP(6);

SizeCalculator sizeCalc = new SizeCalculator();
int intSize = intType.accept(sizeCalc); // Returns 4
int arraySize = arrayType.accept(sizeCalc); // Returns special array handling

TemporalChecker tempChecker = new TemporalChecker();
boolean isIntTemporal = intType.accept(tempChecker); // false
boolean isTimestampTemporal = timestampType.accept(tempChecker); // true

PrecisionExtractor precExtractor = new PrecisionExtractor();
OptionalInt precision = timestampType.accept(precExtractor); // OptionalInt[6]

Related Pages

• Principle:Apache_Paimon_Type_System
• Apache_Paimon_DataTypeVisitor
• Apache_Paimon_DataType