> ### Optional容器 使用Optional容器可以快速的定位NPE，并且在一定程度上可以減少對參數非空檢驗的代碼量。 ``` /** * Optional.of(T t); // 創建一個Optional實例 * Optional.empty(); // 創建一個空的Optional實例 * Optional.ofNullable(T t); // 若T不為null，創建一個Optional實例，否則創建一個空實例 * isPresent(); // 判斷是夠包含值 * orElse(T t); //如果調用對象包含值，返回該值，否則返回T * orElseGet(Supplier s); // 如果調用對象包含值，返回該值，否則返回s中獲取的值 * map(Function f): // 如果有值對其處理，并返回處理后的Optional，否則返回Optional.empty(); * flatMap(Function mapper);// 與map類似。返回值是Optional * */ @Test public void test() { Optional<Employee> of = Optional.of(new Employee("zhangsan", 12)); System.out.println(of.get()); // NEP Optional<Object> of2 = Optional.of(null); Optional<Object> empty = Optional.empty(); } @Test public void test2() { Optional<Object> empty = Optional.empty(); System.out.println(empty); // No value present System.out.println(empty.get()); } @Test public void test3() { Optional<Employee> ofNullable = Optional.ofNullable(new Employee("zhangsan", 12)); System.out.println(ofNullable); System.out.println(ofNullable.isPresent()); System.out.println(ofNullable.orElse(new Employee("je", 12))); Optional<Object> ofNullable2 = Optional.ofNullable(null); System.out.println(ofNullable2); System.out.println(ofNullable2.isPresent()); System.out.println(ofNullable2.orElse(new Employee("je", 12))); System.out.println(ofNullable2.orElse(null)); } @Test public void test4() { Optional<Employee> ofNullable = Optional.ofNullable(new Employee("zhangsan", 12)); System.out.println(ofNullable.orElseGet(()-> new Employee())); Optional<Object> ofNullable2 = Optional.ofNullable(null); System.out.println(ofNullable2.orElseGet(()-> new Employee())); } @Test public void test5() { Optional<Employee> ofNullable = Optional.ofNullable(new Employee("zhangsan", 12)); System.out.println(ofNullable.map(e->e.getEmployeeName())); System.out.print(ofNullable.flatMap(e->Optional.of(e.getEmployeeName()))); } ``` ***** 原文鏈接：https://blog.csdn.net/qq_29411737/article/details/80835658