Added code to access private properties of a class

core-java-modules/core-java-reflection/src/main/java/com/baeldung/reflection/access/privatefields/AccessPrivateProperties.java

@@ -0,0 +1,27 @@
+package com.baeldung.reflection.access.privatefields;
+
+import java.lang.reflect.Field;
+import java.lang.reflect.InvocationTargetException;
+import java.lang.reflect.Method;
+
+public class AccessPrivateProperties {
+
+    public void accessPrivateFields(String declaredField, Object declaredFieldValue, boolean accessible) throws NoSuchFieldException, NullPointerException, IllegalArgumentException, IllegalAccessException {
+        Person person = new Person();
+        Field field = person.getClass()
+            .getDeclaredField(declaredField);
+        field.setAccessible(accessible);
+        field.set(person, declaredFieldValue);
+        System.out.println(person.getName());
+    }
+
+    public void accessPrivateMethods(String declaredMethod, Class<?> parameterType, Object name, boolean accessible) throws NoSuchMethodException, IllegalAccessException, NullPointerException, IllegalArgumentException, InvocationTargetException {
+        Person person = new Person();
+        Method method = person.getClass()
+            .getDeclaredMethod(declaredMethod, parameterType);
+        method.setAccessible(accessible);
+        String greetMessage = (String) method.invoke(person, name);
+        System.out.println(greetMessage);
+    }
+
+}

core-java-modules/core-java-reflection/src/main/java/com/baeldung/reflection/access/privatefields/Person.java

@@ -0,0 +1,18 @@
+package com.baeldung.reflection.access.privatefields;
+
+public class Person {
+    
+    private String name;
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    private String greet(String number) {
+        return "Hi " + Integer.parseInt(number);
+    }
+}

core-java-modules/core-java-reflection/src/test/java/com/baeldung/reflection/access/privatefields/AccessPrivateFieldsUnitTest.java

@@ -0,0 +1,36 @@
+package com.baeldung.reflection.access.privatefields;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+public class AccessPrivateFieldsUnitTest {
+
+    private static AccessPrivateProperties accessPrivateProperties;
+
+    @BeforeAll
+    public static void beforeAll() {
+        accessPrivateProperties = new AccessPrivateProperties();
+    }
+
+    @Test
+    public void testForNoSuchFieldException() {
+        Assertions.assertThrows(NoSuchFieldException.class, () -> accessPrivateProperties.accessPrivateFields("firstName", "John", true));
+    }
+
+    @Test
+    public void testForIllegalAccessException() {
+        Assertions.assertThrows(IllegalAccessException.class, () -> accessPrivateProperties.accessPrivateFields("name", "John", false));
+    }
+
+    @Test
+    public void testForIllegalArgumentException() {
+        Assertions.assertThrows(IllegalArgumentException.class, () -> accessPrivateProperties.accessPrivateFields("name", 25, true));
+    }
+
+    @Test
+    public void testForNullPointerException() {
+        Assertions.assertThrows(NullPointerException.class, () -> accessPrivateProperties.accessPrivateFields(null, "John", true));
+    }
+
+}

core-java-modules/core-java-reflection/src/test/java/com/baeldung/reflection/access/privatefields/AccessPrivateMethodsUnitTest.java

@@ -0,0 +1,43 @@
+package com.baeldung.reflection.access.privatefields;
+
+import java.lang.reflect.InvocationTargetException;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+public class AccessPrivateMethodsUnitTest {
+
+    private static AccessPrivateProperties accessPrivateProperties;
+
+    @BeforeAll
+    public static void beforeAll() {
+        accessPrivateProperties = new AccessPrivateProperties();
+    }
+
+    @Test
+    public void testForNoSuchMethodException() {
+        Assertions.assertThrows(NoSuchMethodException.class, () -> accessPrivateProperties.accessPrivateMethods("greeting", String.class, "5", true));
+    }
+
+    @Test
+    public void testForIllegalAccessException() {
+        Assertions.assertThrows(IllegalAccessException.class, () -> accessPrivateProperties.accessPrivateMethods("greet", String.class, "5", false));
+    }
+
+    @Test
+    public void testForIllegalArgumentException() {
+        Assertions.assertThrows(IllegalArgumentException.class, () -> accessPrivateProperties.accessPrivateMethods("greet", String.class, 5, true));
+    }
+
+    @Test
+    public void testForNullPointerException() {
+        Assertions.assertThrows(NullPointerException.class, () -> accessPrivateProperties.accessPrivateMethods(null, String.class, "5", true));
+    }
+
+    @Test
+    public void testForInvocationTargetException() {
+        Assertions.assertThrows(InvocationTargetException.class, () -> accessPrivateProperties.accessPrivateMethods("greet", String.class, "John", true));
+    }
+
+}