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
if (disposeExecs == null) {
            disposeExecs = new ArrayList();
        }
        
        disposeExecs.add(r);
    }
    
    /**
     * Cancels a runnable that was previously scheduled with <code>disposeExec</code>.
     * Has no effect if the given runnable was not previously registered with
     * disposeExec.
     * 
     * @param r runnable to cancel
     */
    public void cancelDisposeExec(Runnable r) {
        Assert.isNotNull(r);
        
        if (disposeExecs == null) {
            return;
        }
        
        disposeExecs.remove(r);
        
        if (disposeExecs.isEmpty()) {
            disposeExecs = null;
        }
    }
}