Nimrod.

Green Day have one doozy of a flashback of their punk-rock past midway through Nimrod, the California trio’s fifth album. On the song “Platypus (I Hate You)” drummer Tré Cool’s tom-toms and Mike Dirnt’s bass pound like a herd of charging rhinos as singer Billie Joe Armstrong condenses the phrase ” ‘Cause I hate you” into “Cuz-l-hatechew.”

Green Day’s pop future can be glimpsed immediately afterward. “Uptight” rolls in like a wave, a stripped-down surf tune with an engaging, openhearted vocal, before the guitars and the chorus crash in. Then, out with the tide, is a lush, orchestral instrumental, “Last Ride In,” like a lost outtake from a Van Dyke Parks-era Beach Boys session.

Green Day tried to grow up on their previous album, 1995’s Insomniac, but didn’t seem quite sure how to go about it. The lyrics got nastier, and the characters more depraved, while the music clung stubbornly to the brisk tempos and concise melodies of pop-punk formula. With Nimrod, Armstrong’s juvenile sense of humor is back. On “The Grouch,” he complains, “I’m turning out like my dad,” and on the ska romp “King for a Day,” he imagines life as a drag queen. But Armstrong’s teen-slacker protagonists can also sound almost reflective on Nimrod as they slide into an adult world not much more promising than the dazed-and-confused one that they left behind. Lost opportunities are mulled over in “Walking Alone” and “Haushinka,” and a handful are kissed goodbye on “Good Riddance (Time of Your Life).”

The music also takes a broader view, with neo-psychedelic studio touches, acoustic guitar, violins and horns flavoring the attack. Melody is emphasized, and a measure of sincerity is detectable in the singing. “Redundant,” with its chiming, Byrds-ian guitars and soaring vocals, and “Walking Alone,” with its plaintive harmonica, are persuasive midtempo pop songs, while “Good Riddance” is a surprisingly sweet folk anthem buoyed by strings. This music is a long way from Green Day’s apprenticeship at the Gilman Street punk clubs, in Berkeley, Calif. But now that the band has seen the world, it’s only fitting that Green Day should finally make an album that sounds as if it has.