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Switch Statements

What are switch statements used for?

  • Switch statements are often used when you have a menu of options to choose from.
  • Algorithms that use switch statements can also be written with a series of nested if..else statements.
  • Using switch statements instead of a series of nested if..else statements can make code more readable.
  • Default statements are often required to ensure that all cases are addressed, and the switch is exhaustive.

Basic Structure of a Switch Statement

Sometimes multiple case values have the same action associated with it. At these times, you can put a comma between the two cases as follows:

Example 1: Training

Consider the following code segment which assigns students in an organization to a specific training session based on which weeks they can volunteer. Students who can volunteer in weeks 1 and 2, will attend training 1; week 3 will attend training 2; week 4 will attend training 3; and all other weeks will attend training 4.

Your Turn

Let's try it in the Java Playground.

  • Re-written using a switch statement.
    • use the keyword switch followed by the variable that you want to check the cases against.
    • In the body of the switch, there are a series of case statements.
    • Each case value is followed by the -> operator and what statements to do for that case.
    • The arrow symbol -> is used in switch statements and prevents fall through. This means that once a case statement matches, no other statements will be executed.
    • If the values for a case matches the value of the variable, then the statements associated with that case are executed.
  • The re-write is started below.
  • Predict the output of the code.
  • Run the code to determine if your prediction is correct or not. Modify the weekSelected to have the values 2, 3, and 4 and run each one.
  • Add the additional cases that to print Attend training 2 and Attend training 2 for these weeks as well.

Example 2: Calling Methods

Consider a class called Calculator that has methods to calculate the sum and positive difference of two values as follows:

Based on a string input of + for sum and +- for positive difference, we can call the appropriate method using the conditional operator:

Expanding on this example, assume Calculator has product and quotient methods as well, the code would be:

This code could also be re-written as an if..else statement as follows:

Your Turn

Let's try it in the Java Playground

  • The Calculator class is provided for you.
  • Predict the output of the code.
  • Run the code to determine if your prediction is correct.
  • Modify the conditional operator expression to use a switch statement instead.
  • Test you code with different x, y, and input values.

Resources

Calculator - Using Conditionals and Lambda Mini-Lab

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