#### [Guava斷言](https://lingcoder.gitee.io/onjava8/#/book/16-Validating-Your-Code?id=guava%e6%96%ad%e8%a8%80) 因為啟用 Java 本地斷言很麻煩，Guava 團隊添加一個始終啟用的用來替換斷言的**Verify**類。他們建議靜態導入**Verify**方法： ~~~ // validating/GuavaAssertions.java // Assertions that are always enabled. import com.google.common.base.*; import static com.google.common.base.Verify.*; public class GuavaAssertions { public static void main(String[] args) { verify(2 + 2 == 4); try { verify(1 + 2 == 4); } catch(VerifyException e) { System.out.println(e); } try { verify(1 + 2 == 4, "Bad math"); } catch(VerifyException e) { System.out.println(e.getMessage()); } try { verify(1 + 2 == 4, "Bad math: %s", "not 4"); } catch(VerifyException e) { System.out.println(e.getMessage()); } String s = ""; s = verifyNotNull(s); s = null; try { verifyNotNull(s); } catch(VerifyException e) { System.out.println(e.getMessage()); } try { verifyNotNull( s, "Shouldn't be null: %s", "arg s"); } catch(VerifyException e) { System.out.println(e.getMessage()); } } } /* Output: com.google.common.base.VerifyException Bad math Bad math: not 4 expected a non-null reference Shouldn't be null: arg s */ ~~~ 這里有兩個方法，使用變量**verify()**和**verifyNotNull()**來支持有用的錯誤消息。注意，**verifyNotNull()**內置的錯誤消息通常就足夠了，而**verify()**太一般，沒有有用的默認錯誤消息。