edu.umd.cloud9.io
Class Schema

java.lang.Object
  edu.umd.cloud9.io.Schema

All Implemented Interfaces:

Cloneable

public class Schema
extends Object
implements Cloneable

Description of a Tuple's structure. The Schema class keeps track of column names, data types, and default values. The following code fragment illustrates the use of this class:

 public static final Schema MYSCHEMA = new Schema();
 static {
        MYSCHEMA.addField("token", String.class, "");
        MYSCHEMA.addField("int", Integer.class, new Integer(1));
 }
 

The following field types are allowed:

• Basic Java primitives: Boolean, Integer, Long, Float, Double, String
• Classes that implement Writable

Schema instances can be locked to prevent further changes. Any attempt to alter a locked Schema will result in a runtime exception being thrown. If a Schema is not locked, callers are free to add new fields and edit default values.

New Tuple instances can be created directly from Schema objects through the use of the instantiate() method. A call to that method implicitly locks the Schema.

Acknowledgments: much of this code was adapted from the Prefuse Visualization Toolkit.

Author:

Jimmy Lin

Constructor Summary

Schema()
Creates a new empty Schema.

Schema(int n)
Creates a new empty Schema with a starting capacity for a given number of fields.

Schema(String[] names, Class<?>[] types)
Create a new Schema consisting of the given field names and types.

Schema(String[] names, Class<?>[] types, Object[] defaults)
Create a new Schema consisting of the given field names, types, and default field values.

Method Summary

void	addField(String name, Class<?> type) Adds a field to this Schema.
void	addField(String name, Class<?> type, Object defaultValue) Adds a field to this schema.
Object	clone() Creates a copy of this Schema.
boolean	equals(Object o) Compares this Schema with another one for equality.
Object	getDefault(int index) Returns the default value of the field at the given position.
Object	getDefault(String field) Returns the default value of the field with the given name.
int	getFieldCount() Returns the number of fields in this Schema.
int	getFieldIndex(String field) Returns the position of a field given its name.
String	getFieldName(int index) Returns the name of the field at the given position.
Class<?>	getFieldType(int index) Returns the type of the field at the given position.
Class<?>	getFieldType(String field) Returns the type of the field given its name.
int	hashCode() Computes a hashcode for this schema.
Tuple	instantiate() Instantiate a new Tuple instance with this Schema.
Tuple	instantiate(Object... objects) Instantiate a new Tuple instance with this Schema.
boolean	isLocked() Checks if this schema is locked.
Schema	lockSchema() Locks the Schema, preventing any additional changes.
void	setDefault(int index, Object val) Sets the default value for the given field.
void	setDefault(String field, boolean val) Set the default value for the given field as a boolean.
void	setDefault(String field, double val) Set the default value for the given field as a double.
void	setDefault(String field, float val) Set the default value for the given field as a float.
void	setDefault(String field, int val) Sets the default value for the given field as an int.
void	setDefault(String field, long val) Set the default value for the given field as a long.
void	setDefault(String field, Object val) Sets the default value for the given field.
String	toString() Returns a descriptive String for this schema.

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

Schema

public Schema()

Creates a new empty Schema.

Schema

public Schema(int n)

Creates a new empty Schema with a starting capacity for a given number of fields.

Parameters:

n - the number of columns in this schema

Schema

public Schema(String[] names,
              Class<?>[] types)

Create a new Schema consisting of the given field names and types.

Parameters:

names - the field names

types - the field types (as Class instances)

Schema

public Schema(String[] names,
              Class<?>[] types,
              Object[] defaults)

Create a new Schema consisting of the given field names, types, and default field values.

Parameters:

names - the field names

types - the field types (as Class instances)

defaults - the default values for each field

Method Detail

clone

public Object clone()

Creates a copy of this Schema. Cloned copies of a locked Schema will not inherit the locked status.

Overrides:

clone in class Object

See Also:

Object.clone()

lockSchema

public Schema lockSchema()

Locks the Schema, preventing any additional changes. Locked Schemas cannot be unlocked! Cloned copies of a locked schema will not inherit this locked status.

Returns:

a reference to this schema

isLocked

public boolean isLocked()

Checks if this schema is locked. Locked Schemas can not be edited.

Returns:

true if this Schema is locked, false otherwise

addField

public void addField(String name,
                     Class<?> type)

Adds a field to this Schema.

Parameters:

name - the field name

type - the field type (as a Class instance)

Throws:

IllegalArgumentException - if either name or type are null or the name already exists in this schema.

addField

public void addField(String name,
                     Class<?> type,
                     Object defaultValue)

Adds a field to this schema.

Parameters:

name - the field name

type - the field type (as a Class instance)

Throws:

IllegalArgumentException - if either name or type are null or the name already exists in this schema.

getFieldCount

public int getFieldCount()

Returns the number of fields in this Schema.

Returns:

the number of fields in this Schema

getFieldName

public String getFieldName(int index)

Returns the name of the field at the given position.

Parameters:

index - the field index

Returns:

the field name

getFieldIndex

public int getFieldIndex(String field)

Returns the position of a field given its name.

Parameters:

field - the field name

Returns:

the field position index

getFieldType

public Class<?> getFieldType(int index)

Returns the type of the field at the given position.

Parameters:

index - the column index

Returns:

the column type

getFieldType

public Class<?> getFieldType(String field)

Returns the type of the field given its name.

Parameters:

field - the field name

Returns:

the field type

getDefault

public Object getDefault(int index)

Returns the default value of the field at the given position.

Parameters:

index - the field index

Returns:

the field's default value

getDefault

public Object getDefault(String field)

Returns the default value of the field with the given name.

Parameters:

field - the field name

Returns:

the field's default value

setDefault

public void setDefault(int index,
                       Object val)

Sets the default value for the given field.

Parameters:

index - the index position of the field to set the default for

val - the new default value

setDefault

public void setDefault(String field,
                       Object val)

Sets the default value for the given field.

Parameters:

field - the name of field to set the default for

val - the new default value

setDefault

public void setDefault(String field,
                       int val)

Sets the default value for the given field as an int.

Parameters:

field - the name of field to set the default for

val - the new default value

setDefault

public void setDefault(String field,
                       long val)

Set the default value for the given field as a long.

Parameters:

field - the name of field to set the default for

val - the new default value

setDefault

public void setDefault(String field,
                       float val)

Set the default value for the given field as a float.

Parameters:

field - the name of field to set the default for

val - the new default value

setDefault

public void setDefault(String field,
                       double val)

Set the default value for the given field as a double.

Parameters:

field - the name of field to set the default for

val - the new default value

setDefault

public void setDefault(String field,
                       boolean val)

Set the default value for the given field as a boolean.

Parameters:

field - the name of field to set the default for

val - the new default value

equals

public boolean equals(Object o)

Compares this Schema with another one for equality.

Overrides:

equals in class Object

hashCode

public int hashCode()

Computes a hashcode for this schema.

Overrides:

hashCode in class Object

toString

public String toString()

Returns a descriptive String for this schema.

Overrides:

toString in class Object

instantiate

public Tuple instantiate()

Instantiate a new Tuple instance with this Schema. Fields of the newly instantiated Tuple are set to default value.

Returns:

a new Tuple with this Schema

instantiate

public Tuple instantiate(Object... objects)

Instantiate a new Tuple instance with this Schema.

Parameters:

objects - values of each field

Returns:

a new Tuple with this Schema