Question

What’s the difference between Component.isShowing() and Component.isDisplayable()? I want to use them to decide wheter I should stop/start a Timer.

Answer 1

A component
isShowing() when

Determines whether this component is showing on screen. This means
that the component must be visible, and it must be in a container that
is visible and showing.

isShowing() is recursive and checks all parent components, too, but isDisplayable() and isVisible() verify only the state of the component, not that state of its parents.

This means that your component is currently showing on the screen within a Frame, Panel, etc.
setVisible(true) –> isShowing() returns true (in most cases)
setVisible(false) –> isShowing() returns false (in all cases)

isDisplayable() when

Determines whether this component is displayable. A component is
displayable when it is connected to a native screen resource.

A component is made displayable either when it is added to a displayable
containment hierarchy or when its containment hierarchy is made
displayable. A containment hierarchy is made displayable when its
ancestor window is either packed or made visible.

A component is made undisplayable either when it is removed from a
displayable containment hierarchy or when its containment hierarchy is
made undisplayable. A containment hierarchy is made undisplayable when
its ancestor window is disposed.

This means that your component is in a state where it can be shown on the screen but it doesn’t need to be currently shown on the screen to be in a displayable state. E.g., even if setVisible(false) was called on the component before (so the component is “invisible”) the component is still displayable and isDisplayable() will return true.