java - 包含测试失败 Java 的列表

Question

这个问题已经有答案了:

What is a NullPointerException, and how do I fix it? (12 个回答)

contains() method in List not working as expected (2 个回答)

已关闭 4 年前。

我在测试方法 (displayEmployees) 时遇到问题，该方法返回对象的列表。

public class Task {
    static List<Employee> employeeList;

    public static void main(String[] args) {
        Employee employee1 = new Employee("Dobrobaba", "Irina", "Ivanovna",
                "Moskva", 1900, 6);
        Employee employee2 = new Employee("Shmal", "Anna", "Nikolaevna",
                "Krasnodar", 2017, 8);
        Employee employee3 = new Employee("Kerimova", "Niseimhalum", "Magomedmirzaevna",
                "New-York", 2017, 3);
        Employee employee4 = new Employee("Dobryden", "Yuri", "Viktorovich",
                "Auckland", 2014, 11);
        Employee employee5 = new Employee("Lopata", "Leonid", "Nikolaevich",
                "Beijing", 2014, 11);
        employeeList = new ArrayList<>(Arrays.asList(employee1, employee2, employee3, employee4, employee5));
    }

    /**
     * Prints employees' information, which have worked more than 'n' year(s) for now.
     *
     * @param n years quantity
     */
    public static List<Object> displayEmployees(int n) {
        List<Employee> requiredList = new ArrayList<>();
            employeeList.forEach(employee -> {
                if (Year.now().getValue() - employee.getEmploymentYear() >= n) {
                    requiredList.add(employee);
                }
            });
        return Collections.singletonList(requiredList);
    }
}

这就是我尝试进行测试的方式，将两个列表相互进行比较:

public class TaskTest {
    public static void main(String[] args) {
        displayEmployeesTest();
    }

    public static void assertEquals(String testName, List<Object> expected, List<Object> actual) {
        if (expected.equals(actual)) {
            System.out.println(testName + " passed");
        } else {
            System.out.println(testName + " failed: expected " + expected + ", actual " + actual);
        }
    }

    private static void displayEmployeesTest() {
        List<Object> expectedList;
        Employee employee1 = new Employee("Dobrobaba", "Irina", "Ivanovna",
                "Moskva", 1900, 6);
        Employee employee2 = new Employee("Shmal", "Anna", "Nikolaevna",
                "Krasnodar", 2017, 8);
        Employee employee3 = new Employee("Kerimova", "Niseimhalum", "Magomedmirzaevna",
                "New-York", 2017, 3);
        Employee employee4 = new Employee("Dobryden", "Yuri", "Viktorovich",
                "Auckland", 2014, 11);
        Employee employee5 = new Employee("Lopata", "Leonid", "Nikolaevich",
                "Beijing", 2014, 11);
        expectedList = new ArrayList<>(Arrays.asList(employee1, employee4, employee5));

        assertEquals("displayEmployeesTest", expectedList, displayEmployees(3));
    }
}

问题是 - 我在运行 TaskTest 时收到错误“java.lang.NullPointerException”。

出现这个错误的原因是什么？感谢您的关注!

Answer 1

您调用 Task.displayEmployees 而不调用 Task.main，因此 Task 中的 employeeList 字段永远不会初始化