You can define methods and classes within JShell:

jshell> void speak() {
   ...> System.out.println("hello");
   ...> }

jshell> class MyClass {
   ...> void doNothing() {}
   ...> }

No access modifiers are necessary. As with other blocks, semicolons are required inside of method bodies. Keep in mind that, as with variables, it is possible to redefine methods and classes. To see a list of methods or classes, enter /methods or /types at the JShell prompt, respectively.