suggestions for declarative GUI programming in Java

You might have a look at javabuilders; it uses YAML to build Swing UIs.

A simple example from the manual [PDF]:

JFrame:
    name: myFrame
    title: My Frame
    content:
        - JLabel:
            name: myLabel2
            text: My First Label
        - JLabel:
            name: myLabel2
            text: My Second Label

Alternatively:

JFrame:
    name: myFrame
    title: My Frame
    content:
        - JLabel: {name: myLabel2, text: My First Label}
        - JLabel: {name: myLabel2, text: My Second Label}

Or even:

JFrame(name=myFrame,title=My Frame):
    - JLabel(name=myLabel2, text=My First Label)
    - JLabel(name=myLabel2, text=My Second Label)