edu.mit.csail.sdg.alloy4
Class Env<K,V>

java.lang.Object
  edu.mit.csail.sdg.alloy4.Env<K,V>

Type Parameters:

V - - the type for Value

public final class Env<K,V>
extends java.lang.Object

Mutable; implements a undoable map based on hashCode() and equals(); null key and values are allowed.

To be more precise, every key is internally mapped to a list of values.
The put(X,Y) method appends Y onto the end of X's list.
The get(X) method returns the last element in X's list.
The remove(X) method removes the last element in X's list.

This is very useful for representing lexical scoping: when a local variable is introduced with the same name as an existing variable, the new variable "hides" the old mapping; and when the new variable falls out of scope, the previous mapping is once again "revealed".

Constructor Summary

Env()
Constructs an initially empty environment.

Method Summary

void	clear() Removes all mappings.
Env<K,V>	dup() Make a shallow copy of this environment.
V	get(K key) Returns the latest value associated with the key (and returns null if none).
boolean	has(K key) Returns true if the key is mapped to one or more values.
void	put(K key, V value) Associates the key with the value (which can be null).
void	remove(K key) Removes the latest mapping for the key (and if the key had previous mappings, they become visible).

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Env

public Env()

Constructs an initially empty environment.

Method Detail

has

public boolean has(K key)

Returns true if the key is mapped to one or more values.

get

public V get(K key)

Returns the latest value associated with the key (and returns null if none).

Since null is also a possible value, if you get null as the answer, you need to call has(key) to determine whether the key really has a mapping or not.

put

public void put(K key,
                V value)

Associates the key with the value (which can be null).

remove

public void remove(K key)

Removes the latest mapping for the key (and if the key had previous mappings, they become visible). If there are no mappings for the key, then this method does nothing.

clear

public void clear()

Removes all mappings.

dup

public Env<K,V> dup()

Make a shallow copy of this environment.