Java, Java, Java

 

Another selection structure to add to our repertoire is the switch/break structure. It is meant to provide a shorthand way of coding the following type of multiway selection structure:

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Note that each of the conditions in this case involves the equality of an integral variable and an integral value. This type of structure occurs so frequently in programs that most languages contain statements specially designed to handle it. In Java, we use a combination of the switch and break statements to implement multiway selection.

The switch is designed to select one of several actions depending on the value of some integral expression:

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The integralExpression must evaluate to a primitive integral value of type byte, short, int, char, or boolean. It may not be a long, float, double, or a class type. The integralValues must be literals or final vari- ables. They serve as labels in the one or more case clauses that make up the switch statement body. The default clause is optional, but it is a good idea to include it.

A switch statement is executed according to the following rules:

 

 

 

Rule 1. The integralExpression is evaluated.

Rule 2. Control passes to the statements following the case label whose value equals the integralExpression or, if no cases apply, to the default clause.

Rule 3. Beginning at the selected label or at the default, all of the state- ments up to the end of the switch are executed.

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Integral expression

 

Consider the following example:

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In this case, because m equals 2, the following output would be produced:

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Obviously, this output does not match the following if-else multiway selection structure, which would output, simply, m = 2:

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The reason for this disparity is that the switch executes all statements following the label that matches the value of the integralExpression (see again Rule 3 on the previous page).

In order to use the switch as a multiway selection, you must force it to

break out of the case clause after executing that clause’s statements:

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In this example, the break statement causes control to pass to the end of the switch, with the effect being that one and only one case will be executed within the switch. Thus, the output of this code segment will be simply m = 2, matching exactly the behavior of the multiway if-else selection structure (Fig. 6.13).

 

 

 

Figure 6.13: Flowchart of the mul- tiway switch structure. Note that because of the break statement, one and only one case is executed.

 

 

 

 

 

 

 

 

 

 

 

 

 

SELF-STUDY EXERCISES

EXERCISE 6.15Identify any errors in the following switch structures (if there is no error, specify the output):

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( a ) in t k = 0 ; switch ( k ) case 0 :

System . out . p r i n t l n ( ” zero ” ) ;

break ;

case 1 :

System . out . p r i n t l n ( ”one” ) ;

break ;

default :

System . out . p r i n t l n ( ” de fa ult ” ) ;

break ;

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( b ) in t k = 0 ;

switch ( k + 1 )

case 0 :

System . out . p r i n t l n ( ” zero ” ) ;

break ;

case 1 :

System . out . p r i n t l n ( ”one” ) ;

break ;

default :

System . out . p r i n t l n ( ” de fa ult ” ) ;

break ;

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EXERCISE 6.16 Flavors of ice cream are represented as integers where 0 is vanilla, 1 is chocolate, and 2 is strawberry. Write a switch statement that checks an integer variable flavor and prints out the name of the ice cream flavor or prints “Error” in the default case.

 

EXERCISE 6.17 Modify your solution to the previous exercise to use constants (final variables) to represent the ice cream flavors.

 

SECTION 6.11 • OBJECT-ORIENTED DESIGN:Structured Programming 277