Exercises.java

import java.util.Scanner;
import java.lang.Math;

public class Exercises {
  static Scanner keyboard = new Scanner(System.in);
  
  public static void main(String[] args) {
    System.out.println("I wasn't sure which excercises I was supposed to do, "
      + "so I did all the actual programming ones.");
    // Each of these lines will announce an excercise and then run it
    announceExcercise(6); runExcerciseSix();
    announceExcercise(7); runExcerciseSeven();
    announceExcercise(8); runExcerciseEight();
    announceExcercise(9); runExcerciseNine();
    announceExcercise(10); runExcerciseTen();
    announceExcercise(16); runExcerciseSixteen();
    announceExcercise(17); runExcerciseSeventeen();
  }
  
  /**
    * Prints an annoucement that a certain-numbered excercise is about to be
    * run.
    * TODO: Figure out how to metaprogrammatically call an excercise's method
    * as well.
    */
  public static void announceExcercise(int excercise) {
    System.out.println("Enter any key to execute exercise " + excercise + "..."); // \n
    keyboard.next(); // We discard this value, as the purpose of this line is to wait for the user
    
    System.out.println(""); // \n
    System.out.println("Excercise " + excercise + ":");
  }
  
  // --- -- --- * --- -- --- //
  
  /**
    * Executes and prints the answer to excercise 6.
    */
  public static void runExcerciseSix() {
    int age;
    age = 20;
    System.out.println("My age is");
    System.out.println(19);
    
    System.out.println("You just saw:");
    System.out.println("My age is\\n19");
  }
  
  /**
    * Executes excercise 7.
    */
  public static void runExcerciseSeven() {
    System.out.println("1");
    System.out.println("2");
    System.out.println("3");
  }
  
  /**
    * Executes excercise 8.
    */
  public static void runExcerciseEight() {
    System.out.println("Please enter your age:");
    int age;
    age = keyboard.nextInt();
    
    // Let's run some validation on the user input, just to be safe...
    if((age > 0) && (age < 120)) {
      System.out.println("You are apparently " + age + " years old.");
    } else {
      System.out.println("Don't be silly!");
    }
  }
  
  /**
    * Executes excercise 9.
    */
  public static void runExcerciseNine() {
    // TODO: Figure out how to get the current date from the system
    // First we need to know what year it is...
    System.out.println("Please enter the current year: (yyyy)");
    int currentYear = keyboard.nextInt();
    
    // Some validation on the currentYear user entry
    if(currentYear < 2008) {
      // Since this was written in 2008, I know it's now or later.
      System.out.println("Hah. Nice try.");
      return;
    }
    
    // Then their year of birth
    System.out.println("Please enter your year of birth: (yyyy)");
    int yearBorn = keyboard.nextInt();
    
    // Some validation on the yearBorn user entry
    if(yearBorn > currentYear) {
      System.out.println("What are you, from the future?");
      return;
    }
    
    int age = currentYear - yearBorn;
    
    // More validation, now on the combination of the two user inputs so far.
    if(age < 120) {
      System.out.println("You are apparently " + age + " years old.");
    } else {
      System.out.println("Don't be silly!");
      return;
    }
    
    System.out.println("Finally, enter your age at the year you're looking for:");
    int target = keyboard.nextInt();
    
    int result = yearBorn + target;
    if(age < target) {
      System.out.println("Okay! According to my calculations, you will be "
        + target + " years old in... " + result + "!");
    } else if(age > target) {
      System.out.println("Okay! According to my calculations, you were "
        + target + " years old in... " + result + "!");
    } else {
      System.out.println("You are *currently* " + target + " years old!");
    }
  }
  
  /**
    * Executes excercise 10.
    */
  public static void runExcerciseTen() {
    System.out.println("Please enter one integer, then hit return, and enter another:");
    int firstInt = keyboard.nextInt();
    int secondInt = keyboard.nextInt();
    
    // We're looking for a 'distance' on the number line, aka an absolute value
    int diff = Math.abs(secondInt - firstInt) + 1;
    
    System.out.println("There are " + diff + " integers between "
      + firstInt + " and " + secondInt);
  }
  
  /**
    * Executes excercise 16.
    */
  public static void runExcerciseSixteen() {
    System.out.println("Please enter one integer, then hit return, and enter another:");
    int firstInt = keyboard.nextInt();
    int secondInt = keyboard.nextInt();
    
    // We're looking for a 'distance' on the number line, aka an absolute value
    int diff = Math.abs(secondInt - firstInt) + 1;
    
    System.out.println("There are " + diff + " integers between "
      + firstInt + " and " + secondInt);
  }
  
  /**
    * Executes excercise 17.
    * TODO: Figure out how to acquire an array of abitrary size from user input.
    */
  public static void runExcerciseSeventeen() {
    int[] arr = {5, 80, 12, 19, 56};
    int largest = 0;
    
    // This, while wordy, should be a little faster than the traditional
    // for(){} loop used to iterate arrays. Saves you checking the bounds.
    try {
      for(int i = 0 ;; i++) {
        // TODO: Profile to figure out if it's more efficient to...
        //  1. Initialize a needless variable, but only have to call arr[i]
        //      once per iteration, even when the block *is* executed!
        //  2. Call arr[i] both places, thus having to call it twice when the
        //      block is actually executed
        int val = arr[i];
        if(largest < val) { largest = val; }
      }
    } catch(ArrayIndexOutOfBoundsException aioobe) {}
    
    System.out.println("The largest is " + largest + ".");
  }
  
}