Schmidt was on the stand for day seven of the jury trial between Oracle and Google. Oracle wrapped up the copyright portion of its arguments Tuesday, allowing Google to begin its defense.
Oracle accuses Google of infringing its Java patents and copyrights in Google's Android software. Google says it did nothing wrong, and used only the parts of Java that Sun made freely available to anyone.
Before joining Google, Schmidt was CTO of Sun Microsystems when it invented Java in the 1990s. Oracle bought Sun about two years ago, giving it the patents and copyrights to the Java platform.
Schmidt gave the jury a brief history of Java, describing its release as "an almost religious moment."
He told the jury that Google had once hoped to partner with Sun to develop Android using Java, but that negotiations broke off because Google wanted Android to be open source, and Sun was unwilling to give up that much control over Java.
Instead, Schmidt said, Google created a "clean room" version of Java that didn't use Sun's protected code. Its engineers invented "a completely different approach" to the way Java worked internally, Schmidt testified.
"It did not use Sun's intellectual property, as I was told," he said.
"I was very comfortable that what we were doing was legally correct," he testified later.
One of Google's arguments in the case is that Sun knew Google was using Java in Android but never complained or asked it to sign a license. That gave Google an "implied license" for Java, if it needed one at all, according to Google's lawyers.
Schmidt said he used to "meet and chat" with former Sun CEO Jonathan Schwartz every six months, and that Schwartz never raised an issue with Google's Java use.
Under cross-examination from David Boies, an attorney for Oracle, Schmidt said one of his meetings with Schwartz was in the cafeteria at Sun's offices in Menlo Park, California.
"When did this recollection of a Menlo Park meeting come to you?" Boies wanted to know.
"I'm not sure," said Schmidt.
Boies read from deposition testimony Schmidt gave before the trial began. In it, Schmidt says he doesn't remember the specifics of his conversations with Schwartz, but that he thought they took place in Schwartz's office and over the phone.
On the stand, Schmidt said he stood by his earlier testimony.
A key question in the case is whether the APIs (application programming interfaces) in Java can be copyrighted. Google argues they can't because they are an essential part of the Java programming language, which both sides agree is freely available for use.
"The Java language is not useful without the ability to make something happen, and what the API does is allow you to make something happen," Schmidt told the jury.
Oracle says the APIs are complex creative works, like the blueprints for a house.
"Did anyone at Sun call the APIs 'blueprints?'" Google's lawyer asked Schmidt.
Schmidt said they did not.
Earlier in the day, Oracle finished its of Andy Rubin, the head of Google's Android division. Boies wanted Rubin to admit that Google knew Sun was concerned about the fragmentation of Java.
The answer could affect any damages awarded to Oracle, and Rubin seemed determined not to give Boies the answer he wanted. He said several times that he didn't know how Sun defined "fragmentation."
The normally calm and measured Boies grew exasperated, at one point raising his voice.
"Did you ever ask what people meant when they talked about fragmentation?" Boies asked.
"No," said Rubin.
"The reason you didn't ask is because you knew perfectly well what fragmentation meant, didn't you sir?" Boies said pointedly.
The trial is divided into three phases, to address copyrights, patents and damages. Oracle is seeking about US$1 billion in damages, as well as an injunction that could force Google to change the way it built Android.
The trial, at the U.S. District Court in San Francisco, is expect to last about eight weeks. It has already seen Oracle CEO and Google CEO give testimony.