core/src/com/google/inject/internal/Messages.java
public static String format(String messageFormat, Object... arguments) {
    for (int i = 0; i < arguments.length; i++) {
      arguments[i] = convert(arguments[i]);
    }
    return String.format(messageFormat, arguments);
  }
public static String format(String messageFormat, Object... arguments) {
    for (int i = 0; i < arguments.length; i++) {
      arguments[i] = convert(arguments[i]);
    }
    return String.format(messageFormat, arguments);
  }
Calls {@link String#format} after converting the arguments using some standard guice formatting
for {@link Key}, {@link Class} and {@link Member} objects.