Java/Development Class/Scanner

Count all vowels inputed from keyboard

 
import java.util.Scanner;
public class CountVowels {
  static Scanner sc = new Scanner(System.in);
  public static void main(String[] args) {
    System.out.print("Enter a string: ");
    String s = sc.nextLine();
    int vowelCount = 0;
    for (int i = 0; i < s.length(); i++) {
      char c = s.charAt(i);
      if ((c == "A") || (c == "a") || (c == "E") || (c == "e") || (c == "I") || (c == "i")
          || (c == "O") || (c == "o") || (c == "U") || (c == "u"))
        vowelCount++;
    }
    System.out.println("That string contains " + vowelCount + " vowels.");
  }
}

Demonstrate findInLine()

/**
 *Output:
28
 */
import java.util.Scanner;
public class MainClass {
  public static void main(String args[]) {
    String instr = "Name: Joe Age: 28 ID: 77";
    Scanner conin = new Scanner(instr);
    conin.findInLine("Age:"); // find Age
    if (conin.hasNext())
      System.out.println(conin.next());
    else
      System.out.println("Error!");
  }
}

Letting the user decide when to quit

 
import java.util.Scanner;
public class MainClass {
  static Scanner sc = new Scanner(System.in);
  public static void main(String[] args) {
    int number = 2;
    String input;
    while (true) {
      System.out.println(number + " ");
      System.out.print("Do you want to keep counting?" + " (Y or N)");
      input = sc.next();
      if (input.equalsIgnoreCase("N"))
        break;
      number += 2;
    }
  }
}

Read int by using Scanner Class

 

import java.util.Scanner;
public class MainClass {
  static Scanner sc = new Scanner(System.in);
  public static void main(String[] args) {
    System.out.print("Enter an integer: ");
    int x = sc.nextInt();
    System.out.println("You entered " + x + ".");
  }
}

Test the input string in the while condition.

 
import java.util.Scanner;
public class MainClass {
  static Scanner sc = new Scanner(System.in);
  public static void main(String[] args) {
    int number = 2;
    String input = "Y";
    while (input.equalsIgnoreCase("Y")) {
      System.out.println(number + " ");
      System.out.print("Do you want to keep counting?" + " (Y or N)");
      input = sc.next();
      number += 2;
    }
  }
}

Use Scanner to compute an average a list of comma-separated values

/**
 *Output:
 Average is 6.2
 */
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.Scanner;
public class MainClass {
  public static void main(String args[]) throws IOException {
    int count = 0;
    double sum = 0.0;
    FileWriter fout = new FileWriter("test.txt");
    fout.write("2, 3.4,    5,6, 7.4, 9.1, 10.5, done");
    fout.close();
    FileReader fin = new FileReader("Test.txt");
    Scanner src = new Scanner(fin);
    src.useDelimiter(", *");
    while (src.hasNext()) {
      if (src.hasNextDouble()) {
        sum += src.nextDouble();
        count++;
      } else {
        String str = src.next();
        if (str.equals("done"))
          break;
        else {
          System.out.println("File format error.");
          return;
        }
      }
    }
    fin.close();
    System.out.println("Average is " + sum / count);
  }
}

Use Scanner to compute an average of the values

/**
 *Output:
 */
import java.util.Scanner;
public class MainClass {
  public static void main(String args[]) {
    Scanner conin = new Scanner(System.in);
    int count = 0;
    double sum = 0.0;
    System.out.println("Enter numbers to average.");
    while (conin.hasNext()) {
      if (conin.hasNextDouble()) {
        sum += conin.nextDouble();
        count++;
      } else {
        String str = conin.next();
        if (str.equals("done"))
          break;
        else {
          System.out.println("Data format error.");
          return;
        }
      }
    }
    System.out.println("Average is " + sum / count);
  }
}

Use Scanner to compute an average of the values in a file

/**
 *Output:
Average is 6.2
 */
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.Scanner;
public class MainClass {
  public static void main(String args[]) throws IOException {
    int count = 0;
    double sum = 0.0;
    FileWriter fout = new FileWriter("test.txt");
    fout.write("2 3.4 5 6 7.4 9.1 10.5 done");
    fout.close();
    FileReader fin = new FileReader("Test.txt");
    Scanner src = new Scanner(fin);
    while (src.hasNext()) {
      if (src.hasNextDouble()) {
        sum += src.nextDouble();
        count++;
      } else {
        String str = src.next();
        if (str.equals("done"))
          break;
        else {
          System.out.println("File format error.");
          return;
        }
      }
    }
    fin.close();
    System.out.println("Average is " + sum / count);
  }
}

use Scanner to read input that contains several different types of data

 
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.Scanner;
class ScanMixed {
  public static void main(String args[]) throws IOException {
    int i;
    double d;
    boolean b;
    String str;
    FileWriter fout = new FileWriter("test.txt");
    fout.write("Testing Scanner 10 12.2 one true two false");
    fout.close();
    FileReader fin = new FileReader("Test.txt");
    Scanner src = new Scanner(fin);
    while (src.hasNext()) {
      if (src.hasNextInt()) {
        i = src.nextInt();
        System.out.println("int: " + i);
      } else if (src.hasNextDouble()) {
        d = src.nextDouble();
        System.out.println("double: " + d);
      } else if (src.hasNextBoolean()) {
        b = src.nextBoolean();
        System.out.println("boolean: " + b);
      } else {
        str = src.next();
        System.out.println("String: " + str);
      }
    }
    fin.close();
  }
}

Use Scanner to read user input

 
import java.util.Scanner;
class Console {
  static Scanner sc = new Scanner(System.in);
  public static boolean askYorN(String prompt) {
    while (true) {
      String answer;
      System.out.print("\n" + prompt + " (Y or N) ");
      answer = sc.next();
      if (answer.equalsIgnoreCase("Y"))
        return true;
      else if (answer.equalsIgnoreCase("N"))
        return false;
    }
  }
}
public class MainClass {
  public static void main(String[] args) {
    while (Console.askYorN("Keep going?")) {
      System.out.println("!");
    }
  }
}

Use Scanner to read various types of data from a file

/**
 *Output:
String: Testing
String: Scanner
int: 10
double: 12.2
String: one
boolean: true
String: two
boolean: false
 */
import java.io.FileReader;
import java.io.FileWriter;
import java.io.IOException;
import java.util.Scanner;
public class MainClass {
  public static void main(String args[]) throws IOException {
    int i;
    double d;
    boolean b;
    String str;
    FileWriter fout = new FileWriter("test.txt");
    fout.write("Testing Scanner 10 12.2 one true two false");
    fout.close();
    FileReader fin = new FileReader("Test.txt");
    Scanner src = new Scanner(fin);
    while (src.hasNext()) {
      if (src.hasNextInt()) {
        i = src.nextInt();
        System.out.println("int: " + i);
      } else if (src.hasNextDouble()) {
        d = src.nextDouble();
        System.out.println("double: " + d);
      } else if (src.hasNextBoolean()) {
        b = src.nextBoolean();
        System.out.println("boolean: " + b);
      } else {
        str = src.next();
        System.out.println("String: " + str);
      }
    }
    fin.close();
  }
}