Merge pull request eugenp#6081 from FDPro/master

dupirefr/[email protected] [BAEL-2424] Retrieving a Java Class Fields Using Reflection

Author: lor6

core-java/src/main/java/com/baeldung/reflection/Employee.java

@@ -0,0 +1,7 @@
+package com.baeldung.reflection;
+
+public class Employee extends Person {
+
+    public int employeeId;
+
+}

core-java/src/main/java/com/baeldung/reflection/MonthEmployee.java

@@ -0,0 +1,7 @@
+package com.baeldung.reflection;
+
+public class MonthEmployee extends Employee {
+
+    private double reward;
+
+}

core-java/src/main/java/com/baeldung/reflection/Person.java

@@ -0,0 +1,8 @@
+package com.baeldung.reflection;
+
+public class Person {
+
+    public String lastName;
+    private String firstName;
+
+}

core-java/src/test/java/com/baeldung/reflection/PersonAndEmployeeReflectionUnitTest.java

@@ -0,0 +1,128 @@
+package com.baeldung.reflection;
+
+import org.junit.Test;
+
+import java.lang.reflect.Field;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+
+import static org.junit.Assert.*;
+
+public class PersonAndEmployeeReflectionUnitTest {
+
+    // Fields names
+    private static final String LAST_NAME_FIELD = "lastName";
+    private static final String FIRST_NAME_FIELD = "firstName";
+    private static final String EMPLOYEE_ID_FIELD = "employeeId";
+    private static final String MONTH_EMPLOYEE_REWARD_FIELD = "reward";
+
+    @Test
+    public void givenPersonClass_whenGetDeclaredFields_thenTwoFields() {
+        // When
+        Field[] allFields = Person.class.getDeclaredFields();
+
+        // Then
+        assertEquals(2, allFields.length);
+
+        Field lastNameField = allFields[0];
+        assertEquals(LAST_NAME_FIELD, lastNameField.getName());
+        assertEquals(String.class, lastNameField.getType());
+
+        Field firstNameField = allFields[1];
+        assertEquals(FIRST_NAME_FIELD, firstNameField.getName());
+        assertEquals(String.class, firstNameField.getType());
+    }
+
+    @Test
+    public void givenEmployeeClass_whenSuperClassGetDeclaredFields_thenOneField() {
+        // When
+        Field[] allFields = Employee.class.getSuperclass().getDeclaredFields();
+
+        // Then
+        assertEquals(2, allFields.length);
+
+        Field lastNameField = allFields[0];
+        assertEquals(LAST_NAME_FIELD, lastNameField.getName());
+        assertEquals(String.class, lastNameField.getType());
+
+        Field firstNameField = allFields[1];
+        assertEquals(FIRST_NAME_FIELD, firstNameField.getName());
+        assertEquals(String.class, firstNameField.getType());
+    }
+
+    @Test
+    public void givenEmployeeClass_whenGetDeclaredFields_thenOneField() {
+        // When
+        Field[] allFields = Employee.class.getDeclaredFields();
+
+        // Then
+        assertEquals(1, allFields.length);
+
+        Field employeeIdField = allFields[0];
+        assertEquals(EMPLOYEE_ID_FIELD, employeeIdField.getName());
+        assertEquals(int.class, employeeIdField.getType());
+    }
+
+    @Test
+    public void givenEmployeeClass_whenGetDeclaredFieldsOnBothClasses_thenThreeFields() {
+        // When
+        Field[] personFields = Employee.class.getSuperclass().getDeclaredFields();
+        Field[] employeeFields = Employee.class.getDeclaredFields();
+        Field[] allFields = new Field[employeeFields.length + personFields.length];
+        Arrays.setAll(allFields, i -> (i < personFields.length ? personFields[i] : employeeFields[i - personFields.length]));
+
+        // Then
+        assertEquals(3, allFields.length);
+
+        Field lastNameField = allFields[0];
+        assertEquals(LAST_NAME_FIELD, lastNameField.getName());
+        assertEquals(String.class, lastNameField.getType());
+
+        Field firstNameField = allFields[1];
+        assertEquals(FIRST_NAME_FIELD, firstNameField.getName());
+        assertEquals(String.class, firstNameField.getType());
+
+        Field employeeIdField = allFields[2];
+        assertEquals(EMPLOYEE_ID_FIELD, employeeIdField.getName());
+        assertEquals(int.class, employeeIdField.getType());
+    }
+
+    @Test
+    public void givenMonthEmployeeClass_whenGetAllFields_thenFourFields() {
+        // When
+        List<Field> allFields = getAllFields(MonthEmployee.class);
+
+        // Then
+        assertEquals(4, allFields.size());
+
+        Field lastNameField = allFields.get(0);
+        assertEquals(LAST_NAME_FIELD, lastNameField.getName());
+        assertEquals(String.class, lastNameField.getType());
+
+        Field firstNameField = allFields.get(1);
+        assertEquals(FIRST_NAME_FIELD, firstNameField.getName());
+        assertEquals(String.class, firstNameField.getType());
+
+        Field employeeIdField = allFields.get(2);
+        assertEquals(EMPLOYEE_ID_FIELD, employeeIdField.getName());
+        assertEquals(int.class, employeeIdField.getType());
+
+        Field monthEmployeeRewardField = allFields.get(3);
+        assertEquals(MONTH_EMPLOYEE_REWARD_FIELD, monthEmployeeRewardField.getName());
+        assertEquals(double.class, monthEmployeeRewardField.getType());
+    }
+
+    public List<Field> getAllFields(Class clazz) {
+        if (clazz == null) {
+            return Collections.emptyList();
+        }
+
+        List<Field> result = new ArrayList<>();
+        result.addAll(getAllFields(clazz.getSuperclass()));
+        result.addAll(Arrays.asList(clazz.getDeclaredFields()));
+        return result;
+    }
+
+}