Overview of This Lesson

A common structure in many programming languages is the "select-case" statement. This kind of statement is a lot like a multi-sided selection and in most cases, can be a lot more powerful and efficient than a multi-sided selection. Java's version of a "case" statement is the switch statement. In this lesson you'll learn to use the switch statement, and why it might be a better choice than the mulit-selection structure.

Pre-Requisites

Before doing this lesson, make sure you've gone over the If Statements tutorial.

The Switch Statement

The switch statement examines one value (e.g. a variable or expression result) and performs an action or actions based on that value. The switch statement can only examine values that are Strings, or that are castable into an int (int, byte, short, and char). You can't use a switch with any other data type.

The general format of a switch statement is:

switch (expression) {
    case value1:
        // execute if expression == value1
        break;
    case value2:
        // execute if expression == value2
        break;
    case value3:
        // execute if expression == value3
        break;
    default:
        // execute if none of the above match
}

Pay close attention to the syntax of this statement:

• The variable you are testing must go after "switch" in brackets.
• Each case statement ends with a colon.
• Don't use braces if a case contains more than one statement.
• "default:" is optional and can be used when none of the cases apply (like an else in a multi-sided if)

You'll also notice the break; statement in each of the case blocks. These are optional, but most of the time you would want to keep them. To see why, run this program:

public class TrySwitch1 {

  public static void main(String[] args) {

    int number = 2;
    switch (number)	{
        case 1:
            System.out.println("one");
        case 2:
            System.out.println("two");
        case 3:
            System.out.println("three");
        default:
            System.out.println("too many!");
    }
  }
}

What output do you expect? What output do you get?

This can actually come in handy:

public class TrySwitch2 {

  public static void main(String[] args) {

    int number = 5;
    switch (number)	{
        case 1:
            System.out.println("only one");
            break;
        case 2:
        case 3:
            System.out.println("a few");
            break;
        case 4:
        case 5:
        case 6:
            System.out.println("a handful");
            break;
        default:
            System.out.println("too many!");
    }
  }
}

Try re-running this program with the values 1, 3, and 9 for the variable number.

Prior to Java 7, you could only use a switch statement with any data type that could be implicitly cast into an int (byte, short, char, and int). In the Java 7 release, the switch statement was given support for String objects:

public class FindProvCode {

    public static void main(String[] args) {

        Scanner in = new Scanner(System.in);

        System.out.println("Enter full province/territory name:")
        String province = in.nextLine();
        String provAbbrev = "";

        switch (province.toLowerCase()) {
            case "alberta":  
            provAbbrev = "AB";
            break;
        case "british columbia": 
            provAbbrev = "BC";
            break;
        case "manitoba": 
            provAbbrev = "MB";
            break;
        case "new brunswick": 
            provAbbrev = "NB";
            break;
        case "newfoundland labrador": 
            provAbbrev = "NL";
            break;
        case "nova scotia": 
            provAbbrev = "NS";
            break;
        case "northwest territories": 
            provAbbrev = "NT";
            break;
        case "nunavut": 
            provAbbrev = "NU";
            break;
        case "ontario": 
            provAbbrev = "ON";
            break;
        case "prince edward island":
        case "pei": 
            provAbbrev = "PE";
            break;
        case "quebec": 
            provAbbrev = "QC";
            break;
        case "saskatchewan": 
            provAbbrev = "SK";
            break;
        case "yukon": 
            provAbbrev = "YT";
            break;
        }
        System.out.println("Official abbreviation for " +
            province + ": " + provAbbrev);
    }
}

Exercises

1. Rewrite the following selection statement as a switch statement:

import java.util.Scanner;

public class IfToSwitch {

    public static void main(String[] args) {

        Scanner keysIn = new Scanner(System.in);
        System.out.println("Enter the shipment status:");
        int status = keysIn.nextInt();

        String action = "";
        if (status == 1) {
            action = "Phone vendor and request delivery.";
        } else if (status == 2) {
            action = "Phone customer and warn of late shipment.";
        } else if (status == 3) {
            action = "Prepare shipping labels.";
        } else if (status == 4)	{
            action = "Order additional product from vendor.";
        } else {
            action = "Error:  Invalid status code.";
        }
        System.out.println(action);
    }
}

2. A restaurant has different specials, depending on the day of the week. Write a program using a switch statement that requests a number from 1 to 7 representing the day of the week (Sunday is 1) and displays the daily special according to the table below:

3. A program is needed to calculate delivery costs to various provinces and territories in Canada. The table below describes how the delivery costs are calculated:

The user will enter the province's official code abbreviation and the program should display the correct delivery cost.

1.

2.

3.