org.nfunk.jep

Class SymbolTable

java.lang.Object

java.util.Dictionary<K,V>

java.util.Hashtable

org.nfunk.jep.SymbolTable

All Implemented Interfaces:

Serializable, Cloneable, Map

Direct Known Subclasses:

XSymbolTable

public class SymbolTable
extends Hashtable

A Hashtable which holds a list of all variables. Heavily changed from Jep-2.24 which was just a Hashtable which stored the values of each variable. Here the Hashtable contains elements of type Variable which contain information about that variable. Rather than using get the methods getValue(String), getVar(String) should be used to return the value or variable. The put method is deprecated and should be replace by one of

• addVariable(String,Object) adds a variable with a given name and value, returns null if variable already exists.
• addConstant(String,Object) adds a 'constant' variable whos value cannot be changed.
• setVarValue(String,Object) sets the value of an existing variable. Returns false if variable does not exist.
• makeVarIfNeeded(String,Object) if necessary creates a variable and set its value.
• makeVarIfNeeded(String) if necessary creates a variable. Does not change the value.

Variables which do not have a value set are deemed to be invalid. When Variables need to be constructed then methods in the VariableFactory should be called, which allows different types of variables to be used.

Both SymbolTable and Variable implement the Observer/Observable pattern. This allows objects to be informed whenever a new variable is created or when its value has been changed. The member class StObservable is used to implement Observer. An example of use is

 public class MyObserver implements Observer
 {
        public void initialise()
        {
                SymbolTable st = j.getSymbolTable();
                st.addObserver(this);
                st.addObserverToExistingVariables(this);
        }
 
        public void update(Observable arg0, Object arg1)
        {
                if(arg0 instanceof Variable)
                        println("Var changed: "+arg0);
                else if(arg0 instanceof SymbolTable.StObservable)
                {
                        println("New var: "+arg1);
 
                        // This line is vital to ensure that 
                        // any new variable created will be observed. 
                        ((Variable) arg1).addObserver(this);
                }
        }
 }
 

Author:

Rich Morris Created on 28-Feb-2004

See Also:

Serialized Form

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
class	SymbolTable.StObservable

Field Summary

Fields

Modifier and Type	Field and Description
protected SymbolTable.StObservable	obeservable

Constructor Summary

Constructors

Constructor and Description
SymbolTable(VariableFactory varFac) SymbolTable should always be constructed an associated variable factory.

Method Summary

Modifier and Type	Method and Description
Variable	addConstant(String name, Object val) Create a constant variable with the given name and value.
void	addObserver(Observer arg) Adds an observer which will be notified when a new variable is created.
void	addObserverToExistingVariables(Observer arg) Adds an observer to all variables currently in the SymbolTable.
Variable	addVariable(String name, Object val) Creates a new variable with given value.
void	clearNonConstants() Remove all non constant elements
void	clearValues() Clears the values of all variables.
int	countObservers()
protected Variable	createVariable(String name)
protected Variable	createVariable(String name, Object val) Returns a new variable fro the variable factory.
void	deleteObserver(Observer arg)
void	deleteObservers()
Object	get(Object key) Deprecated. The getValue or getVar methods should be used instead.
Object	getValue(Object key) Finds the value of the variable with the given name.
Variable	getVar(String name) Finds the variable with given name.
VariableFactory	getVariableFactory() Returns the variable factory of this instance.
boolean	hasChanged()
Variable	makeVarIfNeeded(String name) If necessary create a variable with the given name.
Variable	makeVarIfNeeded(String name, Object val) Create a variable with the given name and value.
Object	put(Object key, Object val) Deprecated. The setVarValue or makeVar methods should be used instead.
void	setVarValue(String name, Object val) Sets the value of variable with the given name.
String	toString() Returns a list of variables, one per line.

Methods inherited from class java.util.Hashtable

clear, clone, compute, computeIfAbsent, computeIfPresent, contains, containsKey, containsValue, elements, entrySet, equals, forEach, getOrDefault, hashCode, isEmpty, keys, keySet, merge, putAll, putIfAbsent, rehash, remove, remove, replace, replace, replaceAll, size, values

Methods inherited from class java.lang.Object

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

Field Detail

obeservable

protected SymbolTable.StObservable obeservable

Constructor Detail

SymbolTable

public SymbolTable(VariableFactory varFac)

SymbolTable should always be constructed an associated variable factory.

Method Detail

get

public Object get(Object key)

Deprecated. The getValue or getVar methods should be used instead.

Specified by:

get in interface Map

Overrides:

get in class Hashtable

getValue

public Object getValue(Object key)

Finds the value of the variable with the given name. Returns null if variable does not exist.

getVar

public Variable getVar(String name)

Finds the variable with given name. Returns null if variable does not exist.

put

public Object put(Object key,
                  Object val)

Deprecated. The setVarValue or makeVar methods should be used instead.

Specified by:

put in interface Map

Overrides:

put in class Hashtable

setVarValue

public void setVarValue(String name,
                        Object val)

Sets the value of variable with the given name.

Throws:

NullPointerException - if the variable has not been previously created with addVariable(String,Object) first.

createVariable

protected Variable createVariable(String name,
                                  Object val)

Returns a new variable fro the variable factory. Notifies observers when a new variable is created. If a subclass need to create a new variable it should call this method.

Parameters:

name -

val -

Returns:

an new Variable object.

createVariable

protected Variable createVariable(String name)

addVariable

public Variable addVariable(String name,
                            Object val)

Creates a new variable with given value.

Parameters:

name - name of variable

val - initial value of variable

Returns:

a reference to the created variable.

addConstant

public Variable addConstant(String name,
                            Object val)

Create a constant variable with the given name and value. Returns null if variable already exists.

makeVarIfNeeded

public Variable makeVarIfNeeded(String name,
                                Object val)

Create a variable with the given name and value. It silently does nothing if the value cannot be set.

Returns:

the Variable.

makeVarIfNeeded

public Variable makeVarIfNeeded(String name)

If necessary create a variable with the given name. If the variable exists its value will not be changed.

Returns:

the Variable.

toString

public String toString()

Returns a list of variables, one per line.

Overrides:

toString in class Hashtable

clearValues

public void clearValues()

Clears the values of all variables. Finer control is available through the Variable.setValidValue method.

getVariableFactory

public VariableFactory getVariableFactory()

Returns the variable factory of this instance.

addObserver

public void addObserver(Observer arg)

Adds an observer which will be notified when a new variable is created. The observer's update method will be called whenever a new variable is created, the second argument of this will be a reference to the new variable.

To find out if the values of variables are changed the Variable.addObserver method should be used.

Parameters:

arg - the observer

See Also:

Observable.addObserver(Observer)

countObservers

public int countObservers()

deleteObserver

public void deleteObserver(Observer arg)

deleteObservers

public void deleteObservers()

hasChanged

public boolean hasChanged()

addObserverToExistingVariables

public void addObserverToExistingVariables(Observer arg)

Adds an observer to all variables currently in the SymbolTable.

Parameters:

arg - the object to be notified when a variable changes.

clearNonConstants

public void clearNonConstants()

Remove all non constant elements