Java Lesson 3: Ifs and Switches

• if ... else
  if statements use the following syntax:
  

          if (test)
          {
              statements;
          }
          else
          {
              other_statements; 
          }
          

• Boolean Tests
  • & Logical AND. Tests both conditions.
  • && Conditional AND. If first condition is false, will not evaluate the second condition.
  • | Logical OR. Tests both conditions.
  • || Conditional OR. If first condition is true, will not evaluate the second condition.
  • ! NOT.
• Switch Statements
  

  •         switch(variable)
                {
                    case value1:
                        statements;
                        break;
                    case value2:
                        statements;
                        break;
                    default:
                        statements;
                }
            

  • Case values must be integral values, such as an int or char.
  • If a case does not end in a break, the program will continue executing case statements until it reaches the next break or the end of the code.
  • The default case will be executed if all others fail. Since it is the last statement, it does not need to end in a break.
• Ternary Operator
  • Also called a "conditional operator", this is a nice shortcut for simple "if ... else" assignments.
  • Syntax:
    

            logical_expression ? true_value : false_value
            

  • Example:
    

            highScore = newScore>currentHigh ? newScore : currentHigh;
            

    
    If the newScore is higher than the current score, then highScore = newScore, otherwise highScore = currentHigh.
• Sample Code:
  

  
  public class LuckyNumber
  {
      public static void main(String[] args)
      {
          /* This script randomly selects a number from 1-100, 
           * prints out the number, identifies it as odd or even,
           * then prints one of five messages.  
           */
  
          int num = (int)(100 * Math.random());
          int quoteNum = (int)(num / 25); 
          
          System.out.println("Your lucky number is: " + num);
  
          if (num%2 == 0)
              System.out.println("This is an even number.");
          else
              System.out.println("This is an odd number.");
  
          switch(quoteNum)
          {
              case 0:
                  System.out.println("May your dark days be few and far between.");
                  break;
              case 1:
                  System.out.println("All that is worthy requires sacrifice.");
                  break;
              case 2:
                  System.out.println("Enjoy the fruits of your work.");
                  break;
              case 3:
                  System.out.println("May you excel in all things.");
                  break;
              default:
                  System.out.println("You are truly blessed.");
          }
      }
  } 
      

  • The Math.random() function generates a random number between 0 and 1.
  • The random number has been explicitly cast as an integer by placing (int) in front of the caluation.