simpledb

Class TupleDesc

java.lang.Object

simpledb.TupleDesc

All Implemented Interfaces:

java.io.Serializable

public class TupleDesc
extends java.lang.Object
implements java.io.Serializable

TupleDesc describes the schema of a tuple.

See Also:

Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	TupleDesc.TDItem A help class to facilitate organizing the information of each field

Field Summary

Fields

Modifier and Type	Field and Description
private static long	serialVersionUID

Constructor Summary

Constructors

Constructor and Description
TupleDesc(Type[] typeAr) Constructor.
TupleDesc(Type[] typeAr, java.lang.String[] fieldAr) Create a new TupleDesc with typeAr.length fields with fields of the specified types, with associated named fields.

Method Summary

Modifier and Type	Method and Description
boolean	equals(java.lang.Object o) Compares the specified object with this TupleDesc for equality.
int	fieldNameToIndex(java.lang.String name) Find the index of the field with a given name.
java.lang.String	getFieldName(int i) Gets the (possibly null) field name of the ith field of this TupleDesc.
Type	getFieldType(int i) Gets the type of the ith field of this TupleDesc.
int	getSize()
int	hashCode()
java.util.Iterator<TupleDesc.TDItem>	iterator()
static TupleDesc	merge(TupleDesc td1, TupleDesc td2) Merge two TupleDescs into one, with td1.numFields + td2.numFields fields, with the first td1.numFields coming from td1 and the remaining from td2.
int	numFields()
java.lang.String	toString() Returns a String describing this descriptor.

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

serialVersionUID

private static final long serialVersionUID

See Also:

Constant Field Values

Constructor Detail

TupleDesc

public TupleDesc(Type[] typeAr,
                 java.lang.String[] fieldAr)

Create a new TupleDesc with typeAr.length fields with fields of the specified types, with associated named fields.

Parameters:

typeAr - array specifying the number of and types of fields in this TupleDesc. It must contain at least one entry.

fieldAr - array specifying the names of the fields. Note that names may be null.

TupleDesc

public TupleDesc(Type[] typeAr)

Constructor. Create a new tuple desc with typeAr.length fields with fields of the specified types, with anonymous (unnamed) fields.

Parameters:

typeAr - array specifying the number of and types of fields in this TupleDesc. It must contain at least one entry.

Method Detail

iterator

public java.util.Iterator<TupleDesc.TDItem> iterator()

Returns:

An iterator which iterates over all the field TDItems that are included in this TupleDesc

numFields

public int numFields()

Returns:

the number of fields in this TupleDesc

getFieldName

public java.lang.String getFieldName(int i)
                              throws java.util.NoSuchElementException

Gets the (possibly null) field name of the ith field of this TupleDesc.

Parameters:

i - index of the field name to return. It must be a valid index.

Returns:

the name of the ith field

Throws:

java.util.NoSuchElementException - if i is not a valid field reference.

getFieldType

public Type getFieldType(int i)
                  throws java.util.NoSuchElementException

Gets the type of the ith field of this TupleDesc.

Parameters:

i - The index of the field to get the type of. It must be a valid index.

Returns:

the type of the ith field

Throws:

java.util.NoSuchElementException - if i is not a valid field reference.

fieldNameToIndex

public int fieldNameToIndex(java.lang.String name)
                     throws java.util.NoSuchElementException

Find the index of the field with a given name.

Parameters:

name - name of the field.

Returns:

the index of the field that is first to have the given name.

Throws:

java.util.NoSuchElementException - if no field with a matching name is found.

getSize

public int getSize()

Returns:

The size (in bytes) of tuples corresponding to this TupleDesc. Note that tuples from a given TupleDesc are of a fixed size.

merge

public static TupleDesc merge(TupleDesc td1,
                              TupleDesc td2)

Merge two TupleDescs into one, with td1.numFields + td2.numFields fields, with the first td1.numFields coming from td1 and the remaining from td2.

Parameters:

td1 - The TupleDesc with the first fields of the new TupleDesc

td2 - The TupleDesc with the last fields of the TupleDesc

Returns:

the new TupleDesc

equals

public boolean equals(java.lang.Object o)

Compares the specified object with this TupleDesc for equality. Two TupleDescs are considered equal if they are the same size and if the n-th type in this TupleDesc is equal to the n-th type in td.

Overrides:

equals in class java.lang.Object

Parameters:

o - the Object to be compared for equality with this TupleDesc.

Returns:

true if the object is equal to this TupleDesc.

hashCode

public int hashCode()

Overrides:

hashCode in class java.lang.Object

toString

public java.lang.String toString()

Returns a String describing this descriptor. It should be of the form "fieldType[0](fieldName[0]), ..., fieldType[M](fieldName[M])", although the exact format does not matter.

Overrides:

toString in class java.lang.Object

Returns:

String describing this descriptor.