BAEL-4089: Accesing private properties of a class in Java (#9441)

* Added code to access private properties of a class

* Removed abstractions to increase simplicity.

* Added unit test cases in givenX_whenY_thenZ format.

* Included test cases for NoSuchFieldException, NoSuchMethodException and
NullPointerException.

* Added new test case for IllegalArgumentException

* Removed test cases for getting private methods

* Added test cases for accessing all data types.

* Segregated test cases for primitive and object types. Added test case
for Autoboxing.

* Condensed fields by removing extra space.

* Added test case for widening.

* Refactored test cases to throw generic Exception

* Created new module core-java-reflection-2

* Revert "Created new module core-java-reflection-2"

This reverts commit 9568663bb2e176eacc2119e605be76577f90b9c6.

* Added new module core-java-reflection-2

* Removed README.MD

core-java-modules/core-java-reflection-2/pom.xml

@@ -0,0 +1,44 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project xmlns="http://maven.apache.org/POM/4.0.0"
+    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+    xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
+    <modelVersion>4.0.0</modelVersion>
+    <artifactId>core-java-reflection-2</artifactId>
+    <version>0.1.0-SNAPSHOT</version>
+    <name>core-java-reflection-2</name>
+    <packaging>jar</packaging>
+    <parent>
+        <groupId>com.baeldung.core-java-modules</groupId>
+        <artifactId>core-java-modules</artifactId>
+        <version>0.0.1-SNAPSHOT</version>
+        <relativePath>../</relativePath>
+    </parent>
+    
+    <build>
+        <finalName>core-java-reflection-2</finalName>
+        <resources>
+            <resource>
+                <directory>src/main/resources</directory>
+                <filtering>true</filtering>
+            </resource>
+        </resources>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-compiler-plugin</artifactId>
+                <version>${maven-compiler-plugin.version}</version>
+                <configuration>
+                    <source>${source.version}</source>
+                    <target>${target.version}</target>
+                    <compilerArgument>-parameters</compilerArgument>
+                </configuration>
+            </plugin>
+        </plugins>
+    </build>
+
+    <properties>
+        <maven-compiler-plugin.version>3.8.0</maven-compiler-plugin.version>
+        <source.version>1.8</source.version>
+        <target.version>1.8</target.version>
+    </properties>
+</project>

core-java-modules/core-java-reflection-2/src/main/java/com/baeldung/reflection/access/privatefields/Person.java

@@ -0,0 +1,87 @@
+package com.baeldung.reflection.access.privatefields;
+
+public class Person {
+
+    private String name = "John";
+    private byte age = 30;
+    private short uidNumber = 5555;
+    private int pinCode = 452002;
+    private long contactNumber = 123456789L;
+    private float height = 6.1242f;
+    private double weight = 75.2564;
+    private char gender = 'M';
+    private boolean active = true;
+
+    public String getName() {
+        return name;
+    }
+
+    public void setName(String name) {
+        this.name = name;
+    }
+
+    public byte getAge() {
+        return age;
+    }
+
+    public void setAge(byte age) {
+        this.age = age;
+    }
+
+    public short getUidNumber() {
+        return uidNumber;
+    }
+
+    public void setUidNumber(short uidNumber) {
+        this.uidNumber = uidNumber;
+    }
+
+    public int getPinCode() {
+        return pinCode;
+    }
+
+    public void setPinCode(int pinCode) {
+        this.pinCode = pinCode;
+    }
+
+    public long getContactNumber() {
+        return contactNumber;
+    }
+
+    public void setContactNumber(long contactNumber) {
+        this.contactNumber = contactNumber;
+    }
+
+    public float getHeight() {
+        return height;
+    }
+
+    public void setHeight(float height) {
+        this.height = height;
+    }
+
+    public double getWeight() {
+        return weight;
+    }
+
+    public void setWeight(double weight) {
+        this.weight = weight;
+    }
+
+    public char getGender() {
+        return gender;
+    }
+
+    public void setGender(char gender) {
+        this.gender = gender;
+    }
+
+    public boolean isActive() {
+        return active;
+    }
+
+    public void setActive(boolean active) {
+        this.active = active;
+    }
+
+}

core-java-modules/core-java-reflection-2/src/test/java/com/baeldung/reflection/access/privatefields/AccessPrivateFieldsUnitTest.java

@@ -0,0 +1,168 @@
+package com.baeldung.reflection.access.privatefields;
+
+import java.lang.reflect.Field;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public class AccessPrivateFieldsUnitTest {
+
+    @Test
+    public void whenGetIntegerFields_thenSuccess() throws Exception {
+        Person person = new Person();
+
+        Field ageField = person.getClass()
+            .getDeclaredField("age");
+        ageField.setAccessible(true);
+
+        byte age = ageField.getByte(person);
+        Assertions.assertEquals(30, age);
+
+        Field uidNumberField = person.getClass()
+            .getDeclaredField("uidNumber");
+        uidNumberField.setAccessible(true);
+
+        short uidNumber = uidNumberField.getShort(person);
+        Assertions.assertEquals(5555, uidNumber);
+
+        Field pinCodeField = person.getClass()
+            .getDeclaredField("pinCode");
+        pinCodeField.setAccessible(true);
+
+        int pinCode = pinCodeField.getInt(person);
+        Assertions.assertEquals(452002, pinCode);
+
+        Field contactNumberField = person.getClass()
+            .getDeclaredField("contactNumber");
+        contactNumberField.setAccessible(true);
+
+        long contactNumber = contactNumberField.getLong(person);
+        Assertions.assertEquals(123456789L, contactNumber);
+
+    }
+
+    @Test
+    public void whenDoAutoboxing_thenSuccess() throws Exception {
+        Person person = new Person();
+
+        Field pinCodeField = person.getClass()
+            .getDeclaredField("pinCode");
+        pinCodeField.setAccessible(true);
+
+        Integer pinCode = pinCodeField.getInt(person);
+        Assertions.assertEquals(452002, pinCode);
+    }
+
+    @Test
+    public void whenDoWidening_thenSuccess() throws Exception {
+        Person person = new Person();
+
+        Field pinCodeField = person.getClass()
+            .getDeclaredField("pinCode");
+        pinCodeField.setAccessible(true);
+
+        Long pinCode = pinCodeField.getLong(person);
+        Assertions.assertEquals(452002L, pinCode);
+    }
+
+    @Test
+    public void whenGetFloatingTypeFields_thenSuccess() throws Exception {
+        Person person = new Person();
+
+        Field heightField = person.getClass()
+            .getDeclaredField("height");
+        heightField.setAccessible(true);
+
+        float height = heightField.getFloat(person);
+        Assertions.assertEquals(6.1242f, height);
+
+        Field weightField = person.getClass()
+            .getDeclaredField("weight");
+        weightField.setAccessible(true);
+
+        double weight = weightField.getDouble(person);
+        Assertions.assertEquals(75.2564, weight);
+    }
+
+    @Test
+    public void whenGetCharacterFields_thenSuccess() throws Exception {
+        Person person = new Person();
+
+        Field genderField = person.getClass()
+            .getDeclaredField("gender");
+        genderField.setAccessible(true);
+
+        char gender = genderField.getChar(person);
+        Assertions.assertEquals('M', gender);
+    }
+
+    @Test
+    public void whenGetBooleanFields_thenSuccess() throws Exception {
+        Person person = new Person();
+
+        Field activeField = person.getClass()
+            .getDeclaredField("active");
+        activeField.setAccessible(true);
+
+        boolean active = activeField.getBoolean(person);
+        Assertions.assertTrue(active);
+    }
+
+    @Test
+    public void whenGetObjectFields_thenSuccess() throws Exception {
+        Person person = new Person();
+
+        Field nameField = person.getClass()
+            .getDeclaredField("name");
+        nameField.setAccessible(true);
+
+        String name = (String) nameField.get(person);
+        Assertions.assertEquals("John", name);
+    }
+
+    @Test
+    public void givenInt_whenGetStringField_thenIllegalArgumentException() throws Exception {
+        Person person = new Person();
+        Field nameField = person.getClass()
+            .getDeclaredField("name");
+        nameField.setAccessible(true);
+
+        Assertions.assertThrows(IllegalArgumentException.class, () -> nameField.getInt(person));
+    }
+
+    @Test
+    public void givenInt_whenGetLongField_thenIllegalArgumentException() throws Exception {
+        Person person = new Person();
+        Field contactNumberField = person.getClass()
+            .getDeclaredField("contactNumber");
+        contactNumberField.setAccessible(true);
+
+        Assertions.assertThrows(IllegalArgumentException.class, () -> contactNumberField.getInt(person));
+    }
+
+    @Test
+    public void whenFieldNotSetAccessible_thenIllegalAccessException() throws Exception {
+        Person person = new Person();
+        Field nameField = person.getClass()
+            .getDeclaredField("name");
+
+        Assertions.assertThrows(IllegalAccessException.class, () -> nameField.get(person));
+    }
+
+    @Test
+    public void whenAccessingWrongProperty_thenNoSuchFieldException() throws Exception {
+        Person person = new Person();
+
+        Assertions.assertThrows(NoSuchFieldException.class, () -> person.getClass()
+            .getDeclaredField("firstName"));
+    }
+
+    @Test
+    public void whenAccessingNullProperty_thenNullPointerException() throws Exception {
+        Person person = new Person();
+
+        Assertions.assertThrows(NullPointerException.class, () -> person.getClass()
+            .getDeclaredField(null));
+    }
+
+}

core-java-modules/pom.xml

@@ -111,6 +111,7 @@
         <module>core-java-perf</module>
 
         <module>core-java-reflection</module>
+        <module>core-java-reflection-2</module>
 
         <module>core-java-security</module>
         <module>core-java-security-2</module>