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.)

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 (remainder in the example above) must have an integer or character value (an example with char values is on page 124). 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

In the code below, replace the cascading if statement with 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;
}

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)
```

Suppose age is a variable that has been declared and given a value. Fill in the blank with a valid Java condition for "age is divisible by 5" in the following if statement.


        if ( _______________________________________________________ )
          System.out.println ("Your age is divisible by 5.");
        else
          System.out.println ("Your age is not divisible by 5.");

Use truth tables to determine whether the following two expressions are equivalent. Show work!
1. !(p || !q)
  ! p || q