public JavaContainerBuilder setMainClass(String mainClass) {
    this.mainClass = mainClass;
    return this;
  }
Sets the container entrypoint with the specified main class. The entrypoint will be left
unconfigured if this method is not called. To find the main class from {@code .class} files,
use {@link MainClassFinder}.

@param mainClass the main class used to start the application
@return this
@see MainClassFinder
jib-core/src/main/java/com/google/cloud/tools/jib/api/JavaContainerBuilder.java