What is the song playing while Uncle Buck is doing the laundry in the microwave and have the clothes on the ceiling fan? Credits say "Java" and it is clearly not. Here is "Java" : https://youtu.be/WJGRgzRrqFU
That is definitely 'Java', not sure which version as it sounds modulated which could be intentional as I'm sure Buck was the type to not have his Hi-Fi equalizers set properly. I don't know which version, it was recorded a few times by Al Hirt, including live versions that were released.
I can only speculate, but it appears that Ira Newborn, who did the music for Uncle Buck, composed a variation on Al Hirt's cover of Allen Toussaint's "Java." It's like the trumpet in Uncle Buck is playing a reversed or inverted version of the lead trumpet from Al Hirt's version.