Introduction to Java

Slides: Download

Software

Please install the Java Development Kit first: Download
We will use professional IDE for Java programming called IntelliJ - please install it. It is available on Linux, Windows and Mac (download the Community Version): IntelliJ Idea IDE

Exercises

Hello World program

public class Main{
   public static void main(String [] argv){
      System.out.println("Hello world!");
   }
}

Variables

public class Main{
   public static void main(String [] argv){
      String name = "Szymon";
      double a = 5;
      double b = 6;
      System.out.println("Hello "+name+". I know that "+
                a+"+"+b+"="+(a+b));
   }
}

Try other mathematical operations. What about power? Try different types: int, double, float, boolean?

Arrays

public class Main{
   public static void main(String [] argv){
      String name = "Szymon";
      double [] arrayOfNumbers = new double[4];
 
      arrayOfNumbers[0] = 6;
      System.out.println("Hello "+name+
        ". The first element in the array " +
        " is "+arrayOfNumbers[0]);
   }
}

Try print out other elements form the array.

If statements

public class Main{
   public static void main(String [] argv){
      String name = "Szymon";
      double [] arrayOfNumbers = new double[4];
 
      arrayOfNumbers[0] = 6;
      if(arrayOfNumbers[0] == 6){
        System.out.println("Yes, it is 6");
      }else if(arrayOfNumbers[0] != 6){
        System.out.println("No it is not 6");
      }
 
   }
}

Try other if statements.

Input

public class Main{
   public static void main(String [] argv){
      String name;
      int age;
      System.out.println("What is your name?");
      Scanner scanner = new Scanner(System.in); 
      name = scanner.nextLine();
      System.out.println("What is your age?");
      age = scanner.nextInt();
 
   }
}

Try to add statement that will ask for the value of pi and print all the information out.

Input and If statements

public class Main{
   public static void main(String [] argv){
      int age;
      Scanner scanner = new Scanner(System.in); 
      System.out.println("What is your age?");
      age = scanner.nextInt();
 
      if(age < 18){
         System.out.println("Access denied")
      }else{
         System.out.println("Access granted")
      }
 
   }
}

Try more if statements. (you are old, wrong number); Read password from the user and test if it is OK. This one is tricky.

Loops I

public class Main{
   public static void main(String [] argv){
      int age;
      Scanner scanner = new Scanner(System.in); 
      while(true){
         System.out.println("What is your age?");
         age = scanner.nextInt();
 
         if(age < 18){
           System.out.println("Access denied")
         }else{
          System.out.println("Access granted")
         }
     }
   }
}

Try to condition the loop on the value of age.

Loops II

public class Main{
   public static void main(String [] argv){
      double numbers []  = new double[5];
 
      Scanner scanner = new Scanner(System.in); 
      for(int i = 0; i < numbers.length; i++){
         numbers[i] = scanner.nextInt();
      }      
   }
}

Use loop to print out the number that you read; Create a program that will print out multiplication table of given size;

Functions

public class Main{
   public static void main(String [] argv){
      double numbers []  = new double[5];
      double numbers2D [][]  = new double[5][3];
      Scanner scanner = new Scanner(System.in); 
      for(int i = 0; i < numbers.length; i++){
         numbers[i] = scanner.nextInt();
      }      
      printOutTheArray(numbers);
   }
 
   public static void printOutTheArray(double [] array){
       for(int i = 0; i < array.length; i++){
         System.out.println(array[i]);
      }  
   }
}

Add statement that will prompt the user for the next number. Use loop to print out the number that you read; Create a program that will print out multiplication table of given size;

The riddle

Write a program that solves the riddle. But now, assume that the sum of processors is 72.

Solution

Main.java

public class Main{
    public static void main(String [] argv){
        int product= 36;
        int sums [][] = new int[product][4];
        int sumIndex = 0;
        System.out.println("----------All possibilities --------");
        for(int first = 1; first <= product; first++ ){
            for(int second = first; second <=product/first; second++){
                for(int third = second; third <= product/(first*second); third++){
                    if((first*second*third) == product) {
                        System.out.println("|" + first + "|" + "|" + second + "|" + "|" + third + "||" + (first * second * third) + " -> " + (first + second + third));
                        sums[sumIndex][0] = first;
                        sums[sumIndex][1] = second;
                        sums[sumIndex][2] = third;
                        sums[sumIndex][3] = first+second+third;
                        sumIndex++;
                    }
                }
            }
        }
 
        System.out.println("----------Ambiguous solutions--------");
        int [][] ambs = findAmbiguous(sums);
        for(int i = 0; i < ambs.length && ambs[i][0] != 0;i++){
            System.out.println("|" + ambs[i][0] + "|" + "|" + ambs[i][1] + "|" + "|" + ambs[i][2] + "||" + (ambs[i][0]+ambs[i][1]+ambs[i][2]));
        }
 
        System.out.println("----------Solution--------");
        int [] solution  = findMostPowerful(ambs);
        if(solution != null) {
            System.out.println("The solution is First: " + solution[0] + " second: " + solution[1] + " and third: " + solution[2]);
        }
 
 
    }
 
    public static int [][] findAmbiguous(int [][] sums){
        int [][] ambiguous = new int[sums.length][3];
        int ambIndex = 0;
        for(int i = 0; i < sums.length && sums[i][3] != 0;i++){
            for(int j = i+1; j < sums.length && sums[j][3] != 0;j++){
                if(sums[i][3] == sums[j][3]){
                    ambiguous[ambIndex][0] = sums[i][0];
                    ambiguous[ambIndex][1] = sums[i][1];
                    ambiguous[ambIndex][2] = sums[i][2];
                    ambIndex++;
                    ambiguous[ambIndex][0] = sums[j][0];
                    ambiguous[ambIndex][1] = sums[j][1];
                    ambiguous[ambIndex][2] = sums[j][2];
                    ambIndex++;
                }
            }
        }
        return ambiguous;
    }
 
    public static int [] findMostPowerful(int [][] ambiguous){
        for(int i = 0;i < ambiguous.length;i++){
            if(ambiguous[i][0] > ambiguous[i][1] && ambiguous[i][0] > ambiguous[i][2]){
                return ambiguous[i];
            }else if(ambiguous[i][1] > ambiguous[i][0] && ambiguous[i][1] > ambiguous[i][2]){
                return ambiguous[i];
            }else if(ambiguous[i][2] > ambiguous[i][0] && ambiguous[i][2] > ambiguous[i][1]){
                return ambiguous[i];
            }
        }
        return null;
    }
}

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Szymon Bobek

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