org.apache.commons.lang3.tuple

Class Pair<L,R>

java.lang.Object

org.apache.commons.lang3.tuple.Pair<L,R>

Type Parameters:

L - the left element type

R - the right element type

All Implemented Interfaces:

Serializable, Comparable<Pair<L,R>>, Map.Entry<L,R>

Direct Known Subclasses:

Diff, ImmutablePair, MutablePair

public abstract class Pair<L,R>
extends Object
implements Map.Entry<L,R>, Comparable<Pair<L,R>>, Serializable

A pair consisting of two elements.

This class is an abstract implementation defining the basic API. It refers to the elements as 'left' and 'right'. It also implements the Map.Entry interface where the key is 'left' and the value is 'right'.

Subclass implementations may be mutable or immutable. However, there is no restriction on the type of the stored objects that may be stored. If mutable objects are stored in the pair, then the pair itself effectively becomes mutable.

Since:

3.0

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
static Pair<?,?>[]	EMPTY_ARRAY An empty array.

Constructor Summary

Constructors

Constructor and Description
Pair()

Method Summary

Modifier and Type	Method and Description
int	compareTo(Pair<L,R> other) Compares the pair based on the left element followed by the right element.
static <L,R> Pair<L,R>[]	emptyArray() Returns the empty array singleton that can be assigned without compiler warning.
boolean	equals(Object obj) Compares this pair to another based on the two elements.
L	getKey() Gets the key from this pair.
abstract L	getLeft() Gets the left element from this pair.
abstract R	getRight() Gets the right element from this pair.
R	getValue() Gets the value from this pair.
int	hashCode() Returns a suitable hash code.
static <L,R> Pair<L,R>	of(L left, R right) Creates an immutable pair of two objects inferring the generic types.
static <L,R> Pair<L,R>	of(Map.Entry<L,R> pair) Creates an immutable pair from an existing pair.
String	toString() Returns a String representation of this pair using the format ($left,$right).
String	toString(String format) Formats the receiver using the given format.

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.util.Map.Entry

comparingByKey, comparingByKey, comparingByValue, comparingByValue, setValue

Field Detail

EMPTY_ARRAY

public static final Pair<?,?>[] EMPTY_ARRAY

An empty array.

Consider using emptyArray() to avoid generics warnings.

Since:

3.10.

Constructor Detail

Pair

public Pair()

Method Detail

emptyArray

public static <L,R> Pair<L,R>[] emptyArray()

Returns the empty array singleton that can be assigned without compiler warning.

Type Parameters:

L - the left element type

R - the right element type

Returns:

the empty array singleton that can be assigned without compiler warning.

Since:

3.10.

of

public static <L,R> Pair<L,R> of(L left,
                                 R right)

Creates an immutable pair of two objects inferring the generic types.

This factory allows the pair to be created using inference to obtain the generic types.

Type Parameters:

L - the left element type

R - the right element type

Parameters:

left - the left element, may be null

right - the right element, may be null

Returns:

a pair formed from the two parameters, not null

of

public static <L,R> Pair<L,R> of(Map.Entry<L,R> pair)

Creates an immutable pair from an existing pair.

This factory allows the pair to be created using inference to obtain the generic types.

Type Parameters:

L - the left element type

R - the right element type

Parameters:

pair - the existing pair.

Returns:

a pair formed from the two parameters, not null

Since:

3.10

compareTo

public int compareTo(Pair<L,R> other)

Compares the pair based on the left element followed by the right element. The types must be Comparable.

Specified by:

compareTo in interface Comparable<Pair<L,R>>

Parameters:

other - the other pair, not null

Returns:

negative if this is less, zero if equal, positive if greater

equals

public boolean equals(Object obj)

Compares this pair to another based on the two elements.

Specified by:

equals in interface Map.Entry<L,R>

Overrides:

equals in class Object

Parameters:

obj - the object to compare to, null returns false

Returns:

true if the elements of the pair are equal

getKey

public final L getKey()

Gets the key from this pair.

This method implements the Map.Entry interface returning the left element as the key.

Specified by:

getKey in interface Map.Entry<L,R>

Returns:

the left element as the key, may be null

getLeft

public abstract L getLeft()

Gets the left element from this pair.

When treated as a key-value pair, this is the key.

Returns:

the left element, may be null

getRight

public abstract R getRight()

Gets the right element from this pair.

When treated as a key-value pair, this is the value.

Returns:

the right element, may be null

getValue

public R getValue()

Gets the value from this pair.

This method implements the Map.Entry interface returning the right element as the value.

Specified by:

getValue in interface Map.Entry<L,R>

Returns:

the right element as the value, may be null

hashCode

public int hashCode()

Returns a suitable hash code. The hash code follows the definition in Map.Entry.

Specified by:

hashCode in interface Map.Entry<L,R>

Overrides:

hashCode in class Object

Returns:

the hash code

toString

public String toString()

Returns a String representation of this pair using the format ($left,$right).

Overrides:

toString in class Object

Returns:

a string describing this object, not null

toString

public String toString(String format)

Formats the receiver using the given format.

This uses Formattable to perform the formatting. Two variables may be used to embed the left and right elements. Use %1$s for the left element (key) and %2$s for the right element (value). The default format used by toString() is (%1$s,%2$s).

Parameters:

format - the format string, optionally containing %1$s and %2$s, not null

Returns:

the formatted string, not null