单击后重命名按钮 - Java JButton

I'm trying to change my button from saying "Start" to "Stop" when I click on it. My attempt at doing this is below, I looked it up and tried to copy the guides but I don't see what I'm doing wrong. I might be missing some "}" because I left out a lot of the code that's irrelevant. Can someone see what I'm doing wrong? I'm trying to change my button from saying "Sta