SAN FRANCISCO—Top Android programmer Dan Bornstein returned to the stand today as the Oracle v. Google trial rolled into its sixth day.

Oracle, which acquired Java when it purchased Sun Microsystems in 2010, says Google infringed its copyrights by using 37 Java APIs in Android. In 2012, a judge ruled that APIs can't be copyrighted at all, but an appeals court disagreed. Now Oracle may seek up to $9 billion in damages, while Google is arguing that its use of the 37 APIs constitutes "fair use."

Bornstein, who wore a silver tie, clear glasses, and his trademark Android lapel pin, was on the stand for less than half an hour today. He answered friendlier "redirect" questions from Google attorney Christa Anderson, who sought to ameliorate any possible damage from Bornstein's cross-examination last week.

On Friday, Oracle's lawyer had asked Bornstein about e-mails in which he had told his colleagues to avoid using any code from a project called GNU Classpath, "because it was covered by an incompatible license." Oracle's point seemed to be that Bornstein and other Googlers only followed licensing rules when it suited them.

This morning, Anderson pulled up the same e-mails about Classpath.

"To what extent, if at all, does this discussion have anything to do with Google’s decision to implement its own Java APIs in Google?" Anderson asked.

"Nothing," said Bornstein. "GNU Classpath was an independent implementation of Java APIs" and had nothing to do with Google's use of APIs.

Next, Anderson brought up Bornstein's exhortations to his team to scrub a list of banned words from the Android source code, including "Java," "Oracle," "Sun," "license," and "patents."

"You were asked about scrubbing for the 'J-word,' or Java," Anderson said. "Please tell the jury why that was done."

Bornstein answered:

I’m not a lawyer, but I do understand that there’s this thing called trademark law. And I do understand that companies care very much about how their trademarks are used. In order to [use the Java language], you need to use the word Java, literally, in many places in the code. That said, we wanted to be conservative with how to use that term. We did not want to inadvertently violate a trademark.

He also pointed out that nearly all the "scrubbing" was done in the comments, not in the actual implementing code. And it wasn't just trademarks he was scrubbing for—most of it was a hunt for a different kind of "bad words," which he wasn't going to say aloud in court.

"Literally, we were looking for bad words," Bornstein told the jury. "This was code that was going to be visible. And, you know, the S-word and the F-word are not generally considered... professional. So we wanted to get those out."

After the redirect questioning was finished, Oracle's Annette Hurst got a chance to take a parting shot.

"You say you scrubbed the 'J’s' for trademark reasons?" she asked.

"That was the primary concern," Bornstein said.

"We don’t know exactly what you scrubbed, because we don't have it anymore, right?"

"Well, I don't know what you have in evidence, but the way a source code works is that there usually is a historical record."

"Did you bring here any examples today of what you had scrubbed out from the Android source code?" Hurst asked.

"I did not," he answered.

Bornstein stepped down around 8:40am. Next up were a succession of Oracle and Sun employees testifying by video deposition. Testimony will continue through this afternoon.