Java IO Tutorial - Java Scanner

• « Previous
• Next »

To read numbers from the standard input, we have to read it as a string and parse it to a number.

The Scanner class in java.util package reads and parses a text, based on a pattern, into primitive types and strings.

The text source can be an InputStream, a file, a String object, or a Readable object.

We can use a Scanner object to read primitive type values from the standard input System.in.

The following code illustrates how to use the Scanner class by building a trivial calculator to perform addition, subtraction, multiplication, and division.

import java.util.Scanner;
//fromwww.java2s.com
public class Calculator {
 public static void main(String[] args) {
 System.out.println("type something like: 1+3");
 Scanner scanner = new Scanner(System.in);
 double n1 = Double.NaN;
 double n2 = Double.NaN;
 String operation = null;
 try {
 n1 = scanner.nextDouble();
 operation = scanner.next();
 n2 = scanner.nextDouble();
 double result = calculate(n1, n2, operation);
 System.out.printf("%s %s %s = %.2f%n", n1, operation, n2, result);
 }
 catch (Exception e) {
 System.out.println("An invalid expression.");
 }
 }
 public static double calculate(double op1, double op2, String operation) {
 switch (operation) {
 case "+":
 return op1 + op2;
 case "-":
 return op1 - op2;
 case "*":
 return op1 * op2;
 case "/":
 return op1 / op2;
 }
 return Double.NaN;
 }
}

The code above generates the following result.

• Next »
• « Previous