Java 17 Recipes

 How It Works
The switch statement is a control-flow statement that allows you to execute different 
blocks of code based on the value of a switch expression. It is similar to the if-then- else 
statement, except that the switch statement can have only a single test expression. The 
expression type is restricted to one of several different types. When a switch statement 
executes, it evaluates the expression against constants contained in the switch statement’s 
case labels. These case labels are branch points in the code. If the value of the expression 
equals the value of a case label constant, control is transferred to the section of code that 
corresponds to the matching case label. All code statements from that point on are then 
executed until either the end of the switch statement or a break statement is reached. The 
break statement causes the switch statement to terminate, with control being transferred 
to the statement following the switch statement. Optionally, the switch statement can 
contain a default label, which provides a branch point for the case when there is no case 
label constant that equates to the switch expression value.
The SwitchTypeChecker isValidSwitchType() method demonstrates the use of 
a string as the switch test expression. If you closely study the isValidSwitchType() 
method, you see that it tests whether a Class object represents a type that corresponds 
to one of the valid switch expression types. The method also demonstrates how case 
labels can be grouped to implement a logical OR conditional test. If a case label does not 
have any associated code to execute and no break statement, the flow of execution falls 
through to the next closest case label containing executable statements, thus allowing 
common code to be executed if the result of the switch expression matches any one of 
the grouped case constants.
Chapter 7 Data SourCeS anD ColleCtionS

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The RockPaperScissors class implements a command-line rock-paper-scissors 
game, playing against the computer. There are two methods in this class that 
demonstrate the switch statement. The getHand() method shows an enum variable in 
the switch expression. The playHands() method simply intends to show that although 
often a variable, the switch expression can be any expression whose result is of one of the 
allowed switch types. In this case, the expression uses a ternary operator that returns an 
int value.