Query on Recursive composition

For the below relation between Container and Componentin java.awt class hierarchy, I see that,

in addition to is-a relation, class Container has composite relation with class Component with below line of code,

/** 
     * The components in this container.
     * @see #add
     * @see #getComponents
     */
    private java.util.List<Component> component = new java.util.ArrayList<Component>();

But am still not clear with the below diagram wrt operation() method.

So,

1) What does class Leaf and class Composite signify in the below diagram?

2) What exactly are we depicting about operation() method in class Leaf and class Composite as per the below diagram?

Note: I am java beginner learning java