Java Program to Access Private Members of a Class

December 28, 2022

What is class in Java ?

In the Java programming language, a class is a blueprint for creating objects. A class defines the properties and behaviors that objects of that class will have. For example, you might define a class called “Dog” that has properties like breed, color, and size, and behaviors like barking and wagging its tail.

Ways that you can access private members of a class :

1. Use a public getter method: One option is to create a public method in the class that returns the value of the private field. This is called a getter method. For example:

Run

public class Main {
  public static void main(String[] args) {
    MyClass obj = new MyClass();

    // access private field using public getter method
    int fieldValue = obj.getMyField();
    System.out.println(fieldValue);
  }
}

class MyClass {
  private int myField;

  public int getMyField() {
    return myField;
  }
}

Output :

Explanation : Using a public getter method: In this example, the MyClass class has a private field called myField. To access this field from outside the class, we have created a public method called getMyField() that returns the value of the field. In the main class, we create an instance of MyClass and call the getMyField() method to retrieve the value of the private field.

2. Use a public setter method: You can also create a public method in the class that sets the value of the private field. This is called a setter method. For example:

Run

public class Main {
  public static void main(String[] args) {
    MyClass obj = new MyClass();

    // set value of private field using public setter method
    obj.setMyField(123);
  }
}

class MyClass {
  private int myField;

  public void setMyField(int value) {
    myField = value;
  }
}

Output :

...Program finished with exit code 0
Press ENTER to exit console.

Explanation : Using a public setter method: In this example, the MyClass class has a private field called myField. To set the value of this field from outside the class, we have created a public method called setMyField() that takes a value as an argument and assigns it to the private field. In the main class, we create an instance of MyClass and call the setMyField() method to set the value of the private field

3. Use reflection: Another option is to use the Java Reflection API to access the private field or method. Reflection allows you to inspect and manipulate the class at runtime, including accessing private fields and methods. However, this approach is generally discouraged because it can be fragile and can break encapsulation, which is an important principle of OOP.

Run

import java.lang.reflect.Field;

public class Main {
  public static void main(String[] args) throws Exception {
    MyClass obj = new MyClass();

    // use reflection to access private field
    Field field = MyClass.class.getDeclaredField("myField");
    field.setAccessible(true);
    int fieldValue = field.getInt(obj);
    System.out.println(fieldValue);
  }
}

class MyClass {
  private int myField;
}

Output :

Explanation : Using reflection: In this example, we use the Java Reflection API to access the private field myField in the MyClass class. We use the getDeclaredField() method of the Class class to get a Field object for the field, and then call the setAccessible() method to make the field accessible. We can then use the getInt() method to retrieve the value of the field. Reflection allows you to access private members of a class, but it is generally considered a bad practice because it breaks encapsulation and can make your code more fragile.

4. Make the field or method protected: Another option is to change the visibility of the field or method to protected. A protected field or method is accessible from within the class and from any subclass of the class, but not from other classes in the same package.

Run

public class Main {
  public static void main(String[] args) {
    MyClass obj = new MyClass();

    // access protected field from main class
    int fieldValue = obj.myField;
    System.out.println(fieldValue);
  }
}

class MyClass {
  protected int myField;
}

Output :

Explanation : Using a protected field: In this example, the MyClass class has a protected field called myField. A protected field is accessible from within the class and from any subclass of the class. In the main class, we create an instance of MyClass and access the protected field directly.

5. Make the field or method package-private: Finally, you can make the field or method package-private, which means it is only accessible from within the package. To do this, you simply omit the public, private, or protected access modifier. Package-private members are accessible from any class in the same package, but not from classes in other packages.

Run

public class Main {
  public static void main(String[] args) {
    MyClass obj = new MyClass();

    // access package-private field from main class
    int fieldValue = obj.myField;
    System.out.println(fieldValue);
  }
}

class MyClass {
  int myField;
}

Output :

Explanation : Using a package-private field: In this example, the MyClass class has a field called myField that has no access modifier (i.e., it is package-private). A package-private field is only accessible from within the same package as the class. In the main class, we create an instance of MyClass and access the package-private field directly.

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Java Program to Access Private Members of a Class

What is class in Java ?

Ways that you can access private members of a class :

Output :

Output :

Output :

Output :

Output :

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