Java Scanner examples

Long live the Scanner class, a few examples for self-reference.

1. Read Input

1.1 Read input from the console.

JavaScanner1.java

package com.favtuts.io.console;

import java.util.Scanner;

public class JavaScannerExamples {

    public static void main(String[] args) {

        try (Scanner scanner = new Scanner(System.in)) {
            System.out.print("Please enter your name: ");
            String input = scanner.nextLine();
            System.out.println("name : " + input);

            System.out.print("Please enter your age: ");
            int age = scanner.nextInt();
            System.out.println("age : " + age);
        }
    }
    
}

Output

Please enter your name: favtuts
name : favtuts
Please enter your age: 38
age : 38

For scanner.nextInt(), if invalid input, it will throws java.util.InputMismatchException

Please enter your name: favtuts
name : favtuts
Please enter your age: 38wsss
Exception in thread "main" java.util.InputMismatchException
	at java.base/java.util.Scanner.throwFor(Scanner.java:939)
	at java.base/java.util.Scanner.next(Scanner.java:1594)
	at java.base/java.util.Scanner.nextInt(Scanner.java:2258)
	at java.base/java.util.Scanner.nextInt(Scanner.java:2212)
	at com.favtuts.io.console.JavaScannerExamples.main(JavaTest.java:15)

2. Split Input

2.1 By default, the Scanner uses whitespace as delimiters to break its input into tokens.

JavaScanner2.java

package com.favtuts.io.console;

import java.util.Scanner;

public class JavaScannerExamples {

    public static void main(String[] args) {

        // Example 2
        String input = "1,2,3,4,5";
        try (Scanner s = new Scanner(input).useDelimiter(",")) {
            while (s.hasNext()) {
                System.out.println(s.next());
            }
        }
    }
    
}

Output

1
2
3
4
5

3. Read File

3.1 We also can use Scanner to read a file.

JavaScanner3.java

package com.favtuts.io.console;

import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;

public class JavaScannerExamples {

    public static void main(String[] args) {

        // Example 3
        try (Scanner sc = new Scanner(new File("/home/tvt/workspace/favtuts/pom.xml"))) {
            while (sc.hasNext()) {
                System.out.println(sc.nextLine());
            }
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        }
    }
    
}

Download Source Code

$ git clone https://github.com/favtuts/java-core-tutorials-examples

$ cd java-io/console

References

• Scanner JavaDoc
• Java – How to read input from System.console()