Pre-Lab Assignment: Lab 6

Pre-Lab Assignment: Lab 6 Name ___________________________________

The Switch Statement

The Java switch statement (pp. 128 - 132) is another conditional statement. Switch provides a compact, efficient syntax that is useful when you would otherwise have a cascading if statement in which each condition checks the value of the same expression. For example, the if and switch statements below do the same thing -- either could be used as shown in the program. (Note: remainder is a variable of type int and hexDigit is a variable of type String.)

System.out.println("Enter size box you want");
int boxSize = scan.nextInt();
double price;

if (remainder == 10)
{
   hexDigit = "A";
}
else if (remainder == 11) 
{
   hexDigit = "B";     
}
else if (remainder == 12)
{
   hexDigit = "C";
}
else if (remainder == 13)
{
   hexDigit = "D";
}
else if (remainder == 14)
{
   hexDigit = "E";
}
else if (remainder == 15)
{
   hexDigit = "F";
}
else
{
   hexDigit = "Error";
}

switch (remainder)
{
   case 10:
      hexDigit = "A";
      break;
   case 11:
      hexDigit = "B";
      break;
   case 12:
      hexDigit = "C";
      break;
   case 13:
      hexDigit = "D";
      break;
   case 14:
      hexDigit = "E";
      break;
   case 15:
      hexDigit = "F";
      break;
   default:
      hexDigit = "Error";
}

A few things to note about switch statements:

The expression you are switching on (boxSize in the example above) must have an integer or character value (an example with char values is on page 129). It cannot be a boolean, floating point, or object.
The expression is evaluated once and then is matched against each of the cases, starting at the top. When a case matches, all the rest of the code including later cases is executed. However, very often you will only want to execute the code for a single case. To do this, put a break statement after the code for that case; this will break control out of the switch statement, sending it to the next statement in the program. In the above example if we also included remainders less than 10 (as we did in lab 5) we could list all of the cases less than 10 without a break as follows:
```
      switch (remainder)
      {
        case 0:
	case 1:
        case 2:
        case 3:
        case 4:
        case 5:
        case 6:
        case 7:
        case 8:
        case 9:
          hexDigit = "" + remainder;
          break;
        case 10:
          hexDigit = "A";
          break;
        case ...
         
          ...  the rest is as above
       }
```
If no other case matches, default always matches (like else in an if statement).

Exercises

Rewrite the following cascading if statement to a switch statement.

System.out.println("Enter size box you want");
int boxSize = scan.nextInt();
double price;
if (boxSize == 10)
{
   System.out.println("Small");
   price = 2.5;
}
else if (boxSize == 20) 
{
   System.out.println("Medium");     
   price = 3.75;
}
else if (boxSize == 30)
{
   System.out.println("Large");
   price = 5.0;
}
else
{
   System.out.println ("Not a valid size.");
   price = -1;
}

Fix the following code fragment.

if(total == MAX)
	if(total < sum)
		System.out.println("total == MAX and sum total < sum");
else
	System.out.println("total is not equal to MAX");

Rewrite each condition below in valid Java syntax (give a boolean expression):
1. x > y > z
2. neither x nor y is equal to 0
3. both x and y are equal to 0
4. x is greater than y but less than z
Use the laws of logic to write a Java expression equivalent to the following without using the not (!) operator.
```
          ! (age >= 65 && income < 20000)
```
Use truth tables to determine whether each pair of expressions is equivalent.
1. NOT q OR p
  p OR NOT(q OR p)
2. (p AND r) OR (q AND NOT r)
  (p AND q AND NOT r)