Bug 150593 Enhancements for ResourceManager
The attached patch addresses the following in ResourceManager - Fixes several JavaDoc bugs - Adds a "getImage" method that implements the common pattern of "return existing image if known, or allocate a new image otherwise"
bundles/org.eclipse.jface/src/org/eclipse/jface/resource/ResourceManager.java
foundException = e;
            }
        }
        
        if (foundException != null) {
            
            throw foundException;
        }
    }
    
    /**
     * Returns a previously allocated resource associated with the given descriptor, or
     * null if none exists yet. 
     * 
     * @since 3.1
     *
     * @param descriptor descriptor to find
     * @return a previously allocated resource for the given descriptor or null if none.
     */
    public abstract Object find(DeviceResourceDescriptor descriptor);
    
    /**
     * Causes the <code>run()</code> method of the runnable to
     * be invoked just before the receiver is disposed. The runnable
     * can be subsequently canceled by a call to <code>cancelDisposeExec</code>.
     * 
     * @param r runnable to execute.
     */
    public void disposeExec(Runnable r) {
        Assert.isNotNull(r);