Difference Between Private and Public Modifiers in Java

1. Method With the public Modifier in Java
2. Variable With the public Modifier in Java
3. Constructor With the public Modifier in Java
4. Method With the private Modifier in Java
5. Variable With the private Modifier in Java
6. Constructor With the private Modifier in Java

Today we will look at the significant differences between the two access modifiers called private and public, using some examples to understand better.

Method With the public Modifier in Java

When we use the keyword public with a method, its scope expands to the whole program, which means that this method can be accessed by any class and function from other packages too in the same project.

To demonstrate this scenario, we create three classes. The two classes ExampleClass1 and ExampleClass2 are in the same package called com.tutorial while the third class ExampleClass3 is in another package named com.tutorial.javcaTutorial.

In the ExampleClass1 class, we create a method exampleFunc() with the public keyword with a print statement inside. Next, we call this function in the ExampleClass2 class by creating an ExampleClass1 class object.

We also call the exampleFunc() function from ExampleClass3 which is in another package. The whole program runs without any error, which means that the public method is accessible to all these classes.

package com.tutorial;

public class ExampleClass1 {
  public void exampleFunc() {
    System.out.println("exampleFunc() called");
  }
}

package com.tutorial;

public class ExampleClass2 {
  public static void main(String[] args) {
    new ExampleClass1().exampleFunc();
  }
}

package com.tutorial.javaTutorial;

import com.tutorial.ExampleClass1;

public class ExampleClass3 {
  public static void main(String[] args) {
    new ExampleClass1().exampleFunc();
  }
}

Output:

exampleFunc() called

Variable With the public Modifier in Java

A public variable can be accessed from anywhere in the program. As shown in the below example, we can access the showMsg variable from another class by creating its object.

public class ExampleClass1 {
  public String showMsg = "This is a public variable";
}

class ExampleCLass extends ExampleClass1 {
  public static void main(String[] args) {
    System.out.println(new ExampleCLass().showMsg);
  }
}

Output:

This is a public variable

Constructor With the public Modifier in Java

A constructor can also be made public and private like the method and variable. If it is public, we can create an object of the class anywhere like we do in this code.

package com.tutorial;

public class ExampleClass1 {
  public String showMsg;

  public ExampleClass1() {
    showMsg = "Inside a constructor";
  }
}

class ExampleCLass extends ExampleClass1 {
  public static void main(String[] args) {
    System.out.println(new ExampleCLass().showMsg);
  }
}

Output:

Inside a constructor

Method With the private Modifier in Java

Unlike the public access modifier, the private modifier restricts its members by making them non-accessible for out-of-scope classes.

Just like we did in the above section, we create three classes and try to call a function from both the classes. But we use the private modifier instead of public, and we get an error when running the program.

It happens because a private modifier allows access to its members only inside the class that they were declared.

package com.tutorial;

public class ExampleClass1 {
  private void exampleFunc() {
    System.out.println("exampleFunc() called");
  }
}

package com.tutorial;

public class ExampleClass2 {
  public static void main(String[] args) {
    new ExampleClass1().exampleFunc();
  }
}

package com.tutorial.javaTutorial;

import com.tutorial.ExampleClass1;

public class ExampleClass3 {
  public static void main(String[] args) {
    new ExampleClass1().exampleFunc();
  }
}

Output:

java: exampleFunc() has private access in com.tutorial.ExampleClass1

Variable With the private Modifier in Java

We cannot access a private variable from another class even if the variable is in a parent class. It is shown in the following example that when accessed from an of ExampleCLass it throws an error.

public class ExampleClass1 {
  private String showMsg = "This is a public variable";
}

class ExampleCLass extends ExampleClass1 {
  public static void main(String[] args) {
    System.out.println(new ExampleCLass().showMsg);
  }
}

Output:

java: showMsg has private access in com.tutorial.ExampleClass1

Constructor With the private Modifier in Java

A constructor used with the private keyword restricts us from creating an object of the class as a constructor is needed to create an object. We cannot extend the class as its constructor is not available to the subclasses.

The code has two classes, ExampleClass1 contains a variable initialized in the class constructor. We make this constructor private.

When we extend ExampleClass1 in ExampleCLass, we get an error saying that ExampleCLass1() has private access because its constructor is private.

package com.tutorial;

public class ExampleClass1 {
  public String showMsg;

  private ExampleClass1() {
    showMsg = "Inside a constructor";
  }
}

class ExampleCLass extends ExampleClass1 {
  public static void main(String[] args) {
    System.out.println(new ExampleCLass().showMsg);
  }
}

Output:

java: ExampleClass1() has private access in com.tutorial.ExampleClass1