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## org.biojava.utils
Class ChangeSupport

    java.lang.Object
      org.biojava.utils.ChangeSupport

    public class ChangeSupport

extends Object

A utility class to provide management for informing ChangeListeners of ChangeEvents.

This is loosely modelled after the standard PropertyChangeEvent objects.

For an object to correctly fire these events, they must follow a broad outline like this: ``

     public void mutator(foo arg) throw ChangeVetoException {
       ChangeEvent cevt = new ChangeEvent(this, SOME_EVENT_TYPE, arg);
       synchronized(changeSupport) {
         changeSupport.firePreChangeEvent(cevt);
         // update our state using arg
         // ...
         changeSupport.firePostChangeEvent(cevt);
       }
     }

The methods that delegate adding and removing listeners to a ChangeSupport must take responsibility for synchronizing on the delegate.

Since:
  1.1
Author:
  Matthew Pocock, Thomas Down, Keith James (docs), Kalle Naslund (tiny bugfix)

Constructor Summary
`ChangeSupport()` Generate a new ChangeSupport instance.
`ChangeSupport(int initialSize)` Generate a new ChangeSupport instance which has room for initialSize listeners before it needs to grow any resources.
`ChangeSupport(int initialSize, int delta)` Generate a new ChangeSupport instance which has room for initialSize listeners before it needs to grow any resources, and which will grow by delta each time.
`ChangeSupport(Set unchanging)`
`ChangeSupport(Set unchanging, int initialSize, int delta)` Generate a new ChangeSupport instance which has room for initialSize listeners before it needs to grow any resources, and which will grow by delta each time.

Method Summary
`void` | `addChangeListener(ChangeListener cl)` Add a listener that will be informed of all changes.
`void` | `addChangeListener(ChangeListener cl, ChangeType ct)` Add a listener that will be informed of changes of a given type (and it's subtypes)
`String` | `displayString()`
`void` | `firePostChangeEvent(ChangeEvent ce)` Inform the listeners that a change has taken place using their firePostChangeEvent methods.
`void` | `firePreChangeEvent(ChangeEvent ce)` Inform the listeners that a change is about to take place using their firePreChangeEvent methods.
`protected void` | `growIfNecessary()` Grows the internal resources if by adding one more listener they would be full.
`boolean` | `hasListeners()` Return true if we have any listeners registered at all.
`boolean` | `hasListeners(ChangeType ct)` Return true if we have listeners registered for a particular change type.
`boolean` | `isUnchanging(ChangeType ct)`
`protected void` | `reapGarbageListeners()` Remove all references to listeners which have been cleared by the garbage collector.
`void` | `removeChangeListener(ChangeListener cl)` Remove a listener that was interested in all types of changes.
`void` | `removeChangeListener(ChangeListener cl, ChangeType ct)` Remove a listener that was interested in a specific types of changes.

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Constructor Detail

### ChangeSupport

    public ChangeSupport()

  Generate a new ChangeSupport instance.

### ChangeSupport

    public ChangeSupport(int initialSize)

  Generate a new ChangeSupport instance which has room for initialSize listeners before it needs to grow any resources.

  Parameters:
    `initialSize` - the number of listeners that can be added before this needs to grow for the first time

### ChangeSupport

    public ChangeSupport(int initialSize,
                         int delta)

  Generate a new ChangeSupport instance which has room for initialSize listeners before it needs to grow any resources, and which will grow by delta each time.

  Parameters:
    `initialSize` - the number of listeners that can be added before this needs to grow for the first time
    `delta` - the number of listener slots that this will grow by each time it needs to

### ChangeSupport

    public ChangeSupport(Set unchanging)

### ChangeSupport

    public ChangeSupport(Set unchanging,
                         int initialSize,
                         int delta)

  Generate a new ChangeSupport instance which has room for initialSize listeners before it needs to grow any resources, and which will grow by delta each time.

  Parameters:
    `unchanging` - Set of ChangeTypes that can never be fired
    `initialSize` - the number of listeners that can be added before this needs to grow for the first time
    `delta` - the number of listener slots that this will grow by each time it needs to

Method Detail

### hasListeners

    public boolean hasListeners()

  Return true if we have any listeners registered at all.

  Returns:
    true if there are listeners

### hasListeners

    public boolean hasListeners(ChangeType ct)

  Return true if we have listeners registered for a particular change type.

  Parameters:
    `ct` - the ChangeType to check
  Returns:
    true if there are listeners for this type

### addChangeListener

    public void addChangeListener(ChangeListener cl)

  Add a listener that will be informed of all changes.

  Parameters:
    `cl` - the ChangeListener to add

### addChangeListener

    public void addChangeListener(ChangeListener cl,
                                  ChangeType ct)

  Add a listener that will be informed of changes of a given type (and it's subtypes)

  Parameters:
    `cl` - the ChangeListener
    `ct` - the ChangeType it is to be informed of

### growIfNecessary

    protected void growIfNecessary()

  Grows the internal resources if by adding one more listener they would be full.

### removeChangeListener

    public void removeChangeListener(ChangeListener cl)

  Remove a listener that was interested in all types of changes.

  Parameters:
    `cl` - a ChangeListener to remove

### removeChangeListener

    public void removeChangeListener(ChangeListener cl,
                                     ChangeType ct)

  Remove a listener that was interested in a specific types of changes.

  Parameters:
    `cl` - a ChangeListener to remove
    `ct` - the ChangeType that it was interested in

### reapGarbageListeners

    protected void reapGarbageListeners()

  Remove all references to listeners which have been cleared by the garbage collector. This method should only be called when the object is locked.

### firePreChangeEvent

    public void firePreChangeEvent(ChangeEvent ce)
                            throws ChangeVetoException

  Inform the listeners that a change is about to take place using their firePreChangeEvent methods.

  Listeners will be informed if they were interested in all types of event, or if ce.getType() is equal to the type they are registered for.

  This method must be called while the current thread holds the lock on this change support.

  Parameters:
    `ce` - the ChangeEvent to pass on
  Throws:
    `ChangeVetoException` - if any of the listeners veto this change

### firePostChangeEvent

    public void firePostChangeEvent(ChangeEvent ce)

  Inform the listeners that a change has taken place using their firePostChangeEvent methods.

  Listeners will be informed if they were interested in all types of event, or if ce.getType() is equal to the type they are registered for.

  This method must be called while the current thread holds the lock on this change support.

  Parameters:
    `ce` - the ChangeEvent to pass on

### isUnchanging

    public boolean isUnchanging(ChangeType ct)

### displayString

    public String displayString()

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