Package org.eclipse.core.commands

Class Command

java.lang.Object
org.eclipse.core.commands.common.EventManager
org.eclipse.core.commands.common.HandleObject
org.eclipse.core.commands.common.NamedHandleObject
org.eclipse.core.commands.Command
All Implemented Interfaces:
Comparable, IIdentifiable, IObjectWithState
public final class Command extends NamedHandleObject implements Comparable

A command is an abstract representation for some semantic behaviour. It is not the actual implementation of this behaviour, nor is it the visual appearance of this behaviour in the user interface. Instead, it is a bridge between the two.

The concept of a command is based on the command design pattern. The notable difference is how the command delegates responsibility for execution. Rather than allowing concrete subclasses, it uses a handler mechanism (see the handlers extension point). This provides another level of indirection.

A command will exist in two states: defined and undefined. A command is defined if it is declared in the XML of a resolved plug-in. If the plug-in is unloaded or the command is simply not declared, then it is undefined. Trying to reference an undefined command will succeed, but trying to access any of its functionality will fail with a NotDefinedException. If you need to know when a command changes from defined to undefined (or vice versa), then attach a command listener.

Commands are mutable and will change as their definition changes.

Since:
3.1

  • Field Details

    • DEBUG_COMMAND_EXECUTION

      public static boolean DEBUG_COMMAND_EXECUTION
      This flag can be set to true if commands should print information to System.out when executing.

    • DEBUG_HANDLERS

      public static boolean DEBUG_HANDLERS
      This flag can be set to true if commands should print information to System.out when changing handlers.

    • DEBUG_HANDLERS_COMMAND_ID

      public static String DEBUG_HANDLERS_COMMAND_ID
      This flag can be set to a particular command identifier if only that command should print information to System.out when changing handlers.

  • Method Details

    • addCommandListener

      public void addCommandListener(ICommandListener commandListener)
      Adds a listener to this command that will be notified when this command's state changes.
      Parameters:
      commandListener - The listener to be added; must not be null.

    • addExecutionListener

      public void addExecutionListener(IExecutionListener executionListener)
      Adds a listener to this command that will be notified when this command is about to execute.
      Parameters:
      executionListener - The listener to be added; must not be null.

    • addState

      public void addState(String id, State state)

      Adds a state to this command. This will add this state to the active handler, if the active handler is an instance of IObjectWithState.

      A single instance of State cannot be registered with multiple commands. Each command requires its own unique instance.

      Specified by:
      addState in interface IObjectWithState
      Parameters:
      id - The identifier of the state to add; must not be null.
      state - The state to add; must not be null.
      Since:
      3.2
      See Also:

    • compareTo

      public int compareTo(Object object)
      Compares this command with another command by comparing each of its non-transient attributes.
      Specified by:
      compareTo in interface Comparable
      Parameters:
      object - The object with which to compare; must be an instance of Command.
      Returns:
      A negative integer, zero or a postivie integer, if the object is greater than, equal to or less than this command.

    • define

      public void define(String name, String description, Category category)

      Defines this command by giving it a name, and possibly a description as well. The defined property automatically becomes true.

      Notification is sent to all listeners that something has changed.

      Parameters:
      name - The name of this command; must not be null.
      description - The description for this command; may be null.
      category - The category for this command; must not be null.
      Since:
      3.2

    • define

      public void define(String name, String description, Category category, IParameter[] parameters)

      Defines this command by giving it a name, and possibly a description as well. The defined property automatically becomes true.

      Notification is sent to all listeners that something has changed.

      Parameters:
      name - The name of this command; must not be null.
      description - The description for this command; may be null.
      category - The category for this command; must not be null.
      parameters - The parameters understood by this command. This value may be either null or empty if the command does not accept parameters.

    • define

      public void define(String name, String description, Category category, IParameter[] parameters, ParameterType returnType)

      Defines this command by giving it a name, and possibly a description as well. The defined property automatically becomes true.

      Notification is sent to all listeners that something has changed.

      Parameters:
      name - The name of this command; must not be null.
      description - The description for this command; may be null.
      category - The category for this command; must not be null.
      parameters - The parameters understood by this command. This value may be either null or empty if the command does not accept parameters.
      returnType - The type of value returned by this command. This value may be null if the command does not declare a return type.
      Since:
      3.2

    • define

      public void define(String name, String description, Category category, IParameter[] parameters, ParameterType returnType, String helpContextId)

      Defines this command by giving it a name, and possibly a description as well. The defined property automatically becomes true.

      Notification is sent to all listeners that something has changed.

      Parameters:
      name - The name of this command; must not be null.
      description - The description for this command; may be null.
      category - The category for this command; must not be null.
      parameters - The parameters understood by this command. This value may be either null or empty if the command does not accept parameters.
      returnType - The type of value returned by this command. This value may be null if the command does not declare a return type.
      helpContextId - The identifier of the help context to associate with this command; may be null if this command does not have any help associated with it.
      Since:
      3.2

    • execute

      @Deprecated public Object execute(ExecutionEvent event) throws ExecutionException, NotHandledException
      Deprecated.
      Please use executeWithChecks(ExecutionEvent) instead.
      Executes this command by delegating to the current handler, if any. If the debugging flag is set, then this method prints information about which handler is selected for performing this command. This method will succeed regardless of whether the command is enabled or defined. It is generally preferred to call executeWithChecks(ExecutionEvent).
      Parameters:
      event - An event containing all the information about the current state of the application; must not be null.
      Returns:
      The result of the execution; may be null. This result will be available to the client executing the command, and execution listeners.
      Throws:
      ExecutionException - If the handler has problems executing this command.
      NotHandledException - If there is no handler.

    • executeWithChecks

      public Object executeWithChecks(ExecutionEvent event) throws ExecutionException, NotDefinedException, NotEnabledException, NotHandledException
      Executes this command by delegating to the current handler, if any. If the debugging flag is set, then this method prints information about which handler is selected for performing this command. This does checks to see if the command is enabled and defined. If it is not both enabled and defined, then the execution listeners will be notified and an exception thrown.
      Parameters:
      event - An event containing all the information about the current state of the application; must not be null.
      Returns:
      The result of the execution; may be null. This result will be available to the client executing the command, and execution listeners.
      Throws:
      ExecutionException - If the handler has problems executing this command.
      NotDefinedException - If the command you are trying to execute is not defined.
      NotEnabledException - If the command you are trying to execute is not enabled.
      NotHandledException - If there is no handler.
      Since:
      3.2

    • getCategory

      public Category getCategory() throws NotDefinedException
      Returns the category for this command.
      Returns:
      The category for this command; never null.
      Throws:
      NotDefinedException - If the handle is not currently defined.

    • getHandler

      public IHandler getHandler()
      Returns the current handler for this command. This is used by the command manager for determining the appropriate help context identifiers and by the command service to allow handlers to update elements.

      This value can change at any time and should never be cached.

      Returns:
      The current handler for this command; may be null.
      Since:
      3.3

    • getParameter

      public IParameter getParameter(String parameterId) throws NotDefinedException
      Returns the parameter with the provided id or null if this command does not have a parameter with the id.
      Parameters:
      parameterId - The id of the parameter to retrieve.
      Returns:
      The parameter with the provided id or null if this command does not have a parameter with the id.
      Throws:
      NotDefinedException - If the handle is not currently defined.
      Since:
      3.2

    • getParameters

      public IParameter[] getParameters() throws NotDefinedException
      Returns the parameters for this command. This call triggers provides a copy of the array, so excessive calls to this method should be avoided.
      Returns:
      The parameters for this command. This value might be null, if the command has no parameters.
      Throws:
      NotDefinedException - If the handle is not currently defined.

    • getParameterType

      public ParameterType getParameterType(String parameterId) throws NotDefinedException
      Returns the ParameterType for the parameter with the provided id or null if this command does not have a parameter type with the id.
      Parameters:
      parameterId - The id of the parameter to retrieve the ParameterType of.
      Returns:
      The ParameterType for the parameter with the provided id or null if this command does not have a parameter type with the provided id.
      Throws:
      NotDefinedException - If the handle is not currently defined.
      Since:
      3.2

    • getReturnType

      public ParameterType getReturnType() throws NotDefinedException
      Returns the ParameterType for the return value of this command or null if this command does not declare a return value parameter type.
      Returns:
      The ParameterType for the return value of this command or null if this command does not declare a return value parameter type.
      Throws:
      NotDefinedException - If the handle is not currently defined.
      Since:
      3.2

    • isEnabled

      public boolean isEnabled()
      Returns whether this command has a handler, and whether this handler is also handled and enabled.
      Returns:
      true if the command is handled; false otherwise.

    • setEnabled

      public void setEnabled(Object evaluationContext)
      Called be the framework to allow the handler to update its enabled state.
      Parameters:
      evaluationContext - the state to evaluate against. May be null which indicates that the handler can query whatever model that is necessary. This context must not be cached.
      Since:
      3.4

    • isHandled

      public boolean isHandled()
      Returns whether this command has a handler, and whether this handler is also handled.
      Returns:
      true if the command is handled; false otherwise.

    • removeCommandListener

      public void removeCommandListener(ICommandListener commandListener)
      Removes a listener from this command.
      Parameters:
      commandListener - The listener to be removed; must not be null.

    • removeExecutionListener

      public void removeExecutionListener(IExecutionListener executionListener)
      Removes a listener from this command.
      Parameters:
      executionListener - The listener to be removed; must not be null.

    • removeState

      public void removeState(String stateId)

      Removes a state from this command. This will remove the state from the active handler, if the active handler is an instance of IObjectWithState.

      Specified by:
      removeState in interface IObjectWithState
      Parameters:
      stateId - The identifier of the state to remove; must not be null.
      Since:
      3.2

    • setHandler

      public boolean setHandler(IHandler handler)
      Changes the handler for this command. This will remove all the state from the currently active handler (if any), and add it to handler. If debugging is turned on, then this will also print information about the change to System.out.
      Parameters:
      handler - The new handler; may be null if none.
      Returns:
      true if the handler changed; false otherwise.

    • toString

      public String toString()
      The string representation of this command -- for debugging purposes only. This string should not be shown to an end user.
      Specified by:
      toString in class HandleObject
      Returns:
      The string representation; never null.

    • undefine

      public void undefine()
      Makes this command become undefined. This has the side effect of changing the name and description to null. This also removes all state and disposes of it. Notification is sent to all listeners.
      Specified by:
      undefine in class HandleObject

    • getDescription

      public final String getDescription() throws NotDefinedException
      Description copied from class: NamedHandleObject
      Returns the description for this handle.
      Overrides:
      getDescription in class NamedHandleObject
      Returns:
      The description; may be null if there is no description.
      Throws:
      NotDefinedException - If the handle is not currently defined.

    • getName

      public final String getName() throws NotDefinedException
      Description copied from class: NamedHandleObject
      Returns the name for this handle.
      Overrides:
      getName in class NamedHandleObject
      Returns:
      The name for this handle; never null.
      Throws:
      NotDefinedException - If the handle is not currently defined.

    • getState

      public final State getState(String stateId)
      Description copied from interface: IObjectWithState
      Gets the state with the given id.
      Specified by:
      getState in interface IObjectWithState
      Parameters:
      stateId - The identifier of the state to retrieve; must not be null.
      Returns:
      The state; may be null if there is no state with the given id.

    • getStateIds

      public final String[] getStateIds()
      Description copied from interface: IObjectWithState
      Gets the identifiers for all of the state associated with this object.
      Specified by:
      getStateIds in interface IObjectWithState
      Returns:
      All of the state identifiers; may be empty, but never null.