Dot(.) Operator in Java

The dot operator is used to access members of a class or an object. It allows us to:

Access fields (variables) of a class or an object.
Invoke methods of a class or an object.
Access inner classes and interfaces.
The chain method calls for fluent APIs.

1. Accessing Fields using Dot Operator

The dot operator is used to access the fields (variables) of a class or an object.

Example:

Java

// Java Program to demonstrate dot operator
// Used for Accessing Fields 
class Person {
    String name; 
    int age; 
}

// Driver Class
public class Main {
      // Main Function
    public static void main(String[] args) {
          // Initiate Object
        Person person = new Person(); 
        person.name = "John"; 
        person.age = 30; 
      
          // Using Dot Operator
        System.out.println("Name: " + person.name); 
        System.out.println("Age: " + person.age); 
    }
}

Output

Name: John
Age: 30

2. Invoking Methods using Dot Operator

The dot operator is used to invoke methods of a class or an object.

Example:

Java

// Java Program to demonstrate dot operator
// Used for Invoking Methods
class Person {
    String name;
    int age;

    void introduce() {
        System.out.println("Hello, my name is " + name +
                           " and I am " + age + " years old.");
    }
}

public class Main {
    public static void main(String[] args) {
        Person person = new Person();
          
          // Using dot operator 
        person.name = "John";
        person.age = 30;
        person.introduce();
    }
}

Output

Hello, my name is John and I am 30 years old.

3. Accessing Inner Classes and Interfaces using Dot Operator

The dot operator can be used to access inner classes and interfaces within a class.

Example:

Java

// Java Program to implement dot operator
// Used for Accessing Inner Classes and Interfaces
class OuterClass {
    class InnerClass {
        void display() {
            System.out.println("This is an inner class.");
        }
    }
}

// Driver Class
public class Main {
      // Main Function
    public static void main(String[] args) {
        OuterClass outer = new OuterClass();
      
          // Using dot Operator
        OuterClass.InnerClass inner = outer.new InnerClass();
        inner.display();
    }
}

Output

This is an inner class.

4. Chaining Method Calls using Dot Operator

The dot operator allows method chaining, which is a technique used in fluent APIs to call multiple methods in a single statement.

Example:

Java

// Java Program to implement dot operator
// Used for Chaining Method Calls
class Builder {
    private String result = "";

    Builder append(String str) {
        result += str;
        return this;
    }

    String build() {
        return result;
    }
}

// Driver Class
public class Main {
      // Main Function
    public static void main(String[] args) {
        Builder builder = new Builder();
      
          // Using dot Operator
        String result = builder.append("Hello, ").append("world!").build();
        System.out.println(result);
    }
}

Output

Hello, world!

Best Practices and Tips

Always initialize objects before accessing their fields or methods to avoid NullPointerException.
Use method chaining judiciously to improve code readability and maintainability.
Prefer meaningful and descriptive names for fields and methods to enhance code clarity.
Encapsulate fields with private access modifiers and provide public getter and setter methods for controlled access.