Introduction to Programming in Java
===================================

1) Can someone tell me one of the greatest achievements of computer science on
the 90's?

The issue of portability.
A little of the history of Java.

The popularity of Java:
http://www.tiobe.com/index.php/content/paperinfo/tpci/index.html

2) Why is Java so successful?
"simple, object oriented, and familiar".
"robust and secure".
"architecture neutral and portable".
"high performance".

3) How is Java executed?
3.1) What is a VM?
3.2) What are bytecodes?

4) What are primitive types?

// Application 1:
public class Types {
  public static void main(String[] args) {
    short s = 32767;
    char c = (char)65536;
    int i = c; // 5) What will be printed here?
    float f = 1.0F;
    double d = 2.0;
    byte b = 127;
    byte mb = -128;
    // 4.1 Which other primitive types? boolean and long
    System.out.println("int = " + i);
    System.out.println("char = " + c);
    System.out.println("float = " + f);
    System.out.println("double = " + d);
    System.out.println("byte = " + b + ", -byte = " + mb);
    System.out.println("short = " + s);
  }
}

5) What we notice about this program?
- The entry door: main
- The code is enclosed in a class.
- The code to print stuff: System.out
- The C syntax

6) How to write a factorial in Java?
public class Fact {
  public static int fact(int n) {
    if (n > 1)
      return n * fact(n - 1);
    else
      return 1;
  }
  // 6.1) How to read from the input?
  public static void main(String args[]) {
    int n = Integer.parseInt(args[0]);
    System.out.println(fact(n));
  }
}

6.1) Can you do it using a ternary operator?
public static int tf(int n) {
  return n > 1 ? n * fact(n - 1) : 1;
}

7) How to write using while?
  public static int wf(int n) {
    int fact = 1;
    while (n > 1) {
      fact *= n--; // Does this change the 'n' actual parameter?
    }
    return fact;
  }

8) What about using for?
  public static int ff(int n) {
    int fact = 1;
    for (int i = 1; i <= n; i++) {
      fact *= i;
    }
    return fact;
  }

9) What is an array?
9.1) How to write a program to sum up an array of integer?
public class SumArray {
  public static void main(String args[]) {
    int a[] = {2, 4, 8, 2, 3};
    int sum = 0;
    for (int i = 0; i < a.length; i++) {
      sum += a[i];
    }
    System.out.println(sum);
  }
}

10) Contrary to C, Java is strongly typed. What would happen in this C program?
#include <stdio.h>
int main(int argc, char** argv) {
  int i = 0;
  int a[2] = {0, 1};
  printf("argv[1][0] = %c\n", argv[1][0]);
  printf("a[0] = %d\n", a[0]);
  printf("a[1] = %d\n", a[1]);
  printf("a[2] = %d\n", a[2]);
}

11) What is ASCII - American Standard Code for Information Interchange?
11.1) How to write a program to sum up the ASCII code of the letters in the
first input argument?
public class SumVowels {
  public static void main(String args[]) {
    int sum = 0;
    for (int i = 0; i < args[0].length(); i++) {
      sum += args[0].charAt(i);
    }
    System.out.println(sum);
  }
}

11.2) What if we want only the vowels?
public class SumVowels {
  public static void main(String args[]) {
    int sumL = 0, sumU = 0;
    for (int i = 0; i < args[0].length(); i++) {
      char c = args[0].charAt(i);
      System.out.println("Summing " + c + " = " + (int)c);
      switch (c) {
        case 'a': case 'e': case 'i': case 'o': case 'u':
          sumL += c;
          break;
        case 'A': case 'E': case 'I': case 'O': case 'U':
          sumU += c;
      }
    }
    System.out.println(sumL);
    System.out.println(sumU);
  }
}

11.3) Can you make it shorter?
public static void main(String args[]) {
  int sumL = 0, sumU = 0;
  for (int i = 0; i < args[0].length(); i++) {
    char c = args[0].charAt(i);
    System.out.println("Summing " + c + " = " + (int)c);
    if ("aeiou".indexOf(c) != -1) {
      sumL += c;
    } else if ("AEIOU".indexOf(c)
        != -1) {
      sumU += c;
    }
  }
  System.out.println(sumL);
  System.out.println(sumU);
}

12) How to find what we can do with strings?
- http://download.oracle.com/javase/1.5.0/docs/api/java/lang/String.html#indexOf%28int%29

13) How to swap two variables in java?
class Tuple {
  int a;
  int b;
}
public class Swap {
  public static Tuple swapT(int ap, int bp) {
    Tuple t = new Tuple();
    t.a = bp;
    t.b = ap;
    return t;
  }
  public static void swap(int ap, int bp) {
    int tmp = ap;
    ap = bp;
    bp = tmp;
    System.out.println("Swap: a = " + ap + ", b = " + bp);
  }
  public static void main(String args[]) {
    int a = 0, b = 1;
    System.out.println("a = " + a + ", b = " + b);
    swap(a, b);
    System.out.println("a = " + a + ", b = " + b);
    Tuple t = swapT(a, b);
    System.out.println("a = " + t.a + ", b = " +
        t.b);
  }
}

14) How to discover if two strings are anagrams?
public class Anagrams {
  public static void main(String args[]) {
    if (args.length != 2) {
      System.err.println("Syntax: java Anagrams s1 s2");
    } else {
      boolean yes = true;
      String s1 = args[0];
      String s2 = args[1];
      if (s1.length() != s2.length()) {
        yes = false;
      } else {
        int table[] = new int [128];
        for (int i = 0; i < s1.length(); i++) {
          table[s1.charAt(i)]++;
        }
        for (int i = 0; i < s2.length(); i++) {
          if (table[s2.charAt(i)] == 0) {
            yes = false;
            break;
          } else {
            table[s2.charAt(i)]--;
          }
        }
      }
      System.out.println("Are they anagrams? " + yes);
    }
  }
}