John Lynch and the 49ers, who opened the first round with a trade, did it again at the end of the round, sending two picks to Seattle in order to take Alabama linebacker Reuben Foster with the 31st overall pick.

The hard-hitting Foster (6-1, 229) was considered the top inside linebacker in the draft and drew comparisons to former 49ers linebacker Patrick Willis. Foster, in fact, said he modeled his game after Willis and former Ravens linebacker Ray Lewis.

“I want to be that next Patrick Willis (and have people) say, ‘I want to be the next Reuben Foster,’” he said on a conference call. Asked to describe his playing style in one word, Foster picked, “savage.”

At one point in the pre-draft process there was talk that the 49ers might select Foster with their No. 2 overall pick.

His stock dropped, however, after he got into an altercation with a hospital technician at the scouting combine in Indianapolis and was sent home early. He also had a diluted urine sample at the combine, which automatically puts him into the NFL’s drug program. Finally, he recently had surgery on his right shoulder and was unable to work out for teams in the run-up to the draft.

Foster publicly acknowledged his failed urine test last week and reportedly called teams to discuss the issue. As for his shoulder injury, he said he’s 90 percent recovered and will be ready to practice in training camp.

“I’ve got things to prove,” he said. “Big things to prove.”

The 49ers traded their second-round pick, No. 34 overall, as well as one of the picks, No. 111 overall (fourth round), they obtained from the Bears earlier in the day in which the teams also swapped the second and third overall draft picks. They also received Chicago’s No. 67 pick (third round) and a third rounder in next year’s draft.

The 49ers likely are eying Foster as a weak-side linebacker early in his career and someone who possibly could take over for NaVorro Bowman at middle linebacker in coming years.

During the team’s minicamp this week, free-agent acquisition Malcolm Smith lined up at the weak-side spot with the first-string defense. The 49ers signed Smith to a five-year deal worth as much as $26.5 million in March.

The 49ers’ picks

1st: 3, DL Solomon Thomas

1st: 31, LB Reuben Foster

3rd: 66

3rd: 67

4th: 109

4th: 143

5th: 146

5th: 161

6th: 198

6th: 202

7th: 219