← Go home

Nested (Inner) Anonymous Classes in Java

May 2, 2017
Published By : Pratik Kataria
Categorised in: Java Core

Let’s see the Code

import java.util.Scanner;

public class Calculator {

	public static void main( String[] args ){
		Calculator c = new Calculator();
		c.calculate();
	}
	
	protected void calculate() {
		InputHelper helper = new InputHelper();
		String s1 = helper.getInput("Enter a number: ");
		String s2 = helper.getInput("Enter a number: ");
		String op = helper.getInput("Choose an operation (+ - * /): ");

		double result = 0;

		try {
			switch(op) {
				case "+":
					result = MathHelper.addValues(s1, s2);
					break;
				case "-":
					result = MathHelper.subtractValues(s1, s2);
					break;
				case "*":
					result = MathHelper.multiplyValues(s1, s2);
					break;
				case "/":
					result = MathHelper.divideValues(s1, s2);
					break;
				default:
					System.out.println("Invalid operation");
					return;
			}
			System.out.println("The result is: " +result);
		} catch( Exception e ) {
			System.out.println("Number formatting expression: " + e.getMessage());
		}
	}

	class InputHelper {
		private String getInput( String prompt ) {
			System.out.print(prompt);
			Scanner sc = new Scanner(System.in);
			return sc.nextLine();
		}
	}
}

public class MathHelper {
	public static double addValues(String s1, String s2) {
		double d1 = Double.parseDouble(s1);
		double d2 = Double.parseDouble(s2);
		return d1 + d2;
	}

	public static double subtractValues(String s1, String s2) {
		double d1 = Double.parseDouble(s1);
		double d2 = Double.parseDouble(s2);
		return d1 - d2;
	}
	public static double multiplyValues(String s1, String s2) {
		double d1 = Double.parseDouble(s1);
		double d2 = Double.parseDouble(s2);
		return d1 * d2;
	}
	public static double divideValues(String s1, String s2) {
		double d1 = Double.parseDouble(s1);
		double d2 = Double.parseDouble(s2);
		return d1 / d2;
	}

}

Notes:

• MathHelper’s all methods are public.
• Protected denotes the class which can be used by any other class within the same package.
• Calculator c = new Calculator() -> creates an instance of the class
• Above instantiation calls the Calculator() constructor which we haven’t defined. That’s okay since Java creates a no argument constructor automatically.
• If we had protected static void calculate(), we could directly call the calculate() method.
• class InputHelper is the nested class. Thus, getInput() is an instance method of InputHelper class.
• For instance method, we need to created instance. Thus, InputHelper helper = new InputHelper();
• Being a nested class, it is available to only Calculator class since that is where it is defined.
• getInput() is marked private but it can be called because it is in the same code file as Calculator class.

Pratik Kataria

Pratik Kataria is currently learning Springboot and Hibernate.
Technologies known and worked on: C/C++, Java, Python, JavaScript, HTML, CSS, WordPress, Angular, Ionic, MongoDB, SQL and Android.
Softwares known and worked on: Adobe Photoshop, Adobe Illustrator and Adobe After Effects.

pratikkataria.com/