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Programming in Java Netbeans - A Step by Step Tutorial for Beginners: Lesson 9

Danson Wachira is a certified Trainer in Computer Science, Information Technology and related studies.

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Lesson 9: Control Structures in Java – The Switch Statement

programming-in-java-a-step-by-step-tutorial-for-beginners-lesson-9

In Lesson 8, we learnt how to use IF .. ELSE statement. In this lesson we shall learn how to use the Switch statement in Java.

Switch statement is a selection statement, that means when used, it select one value among many values. Switch statement can also be used instead of IF .. ELSE statement. For this lesson, you will need to create yet another class, call it myswitch.

programming-in-java-a-step-by-step-tutorial-for-beginners-lesson-9

The structure of Switch statement in Java looks as follow:

switch(Your test variable) {
case
Testing value:
Statement to be executed;
break;
case
Testing value:
Statement to be executed;
break;
default:
Statement to output if no matching case found;

}

Explaining the Switch statement

The switch statement start with a keyword “switch” (notice it is in lowercase). Inside the round bracket we put the variable that we want to test. What follows is an open curly brace where you start to test your cases. For every case to be tested, you put the keyword case followed by the value you want to test. This value ends with a full colon (:).

After the full colon, the statement(s) that follows is the code you want to be executed if the switch case matches the value you are testing. Remember every statement will end with a semicolon. After the statement(s) is another keyword, break. The break keyword terminates the switch case and takes the program control to the next statement outside the switch statement. Every group of statements ends with a break. Remember to put a semi colon(;) after every break.

If no match was found within all the cases you wanted to test, it is a good practice to let the user know that a matching case was not found. This is handled by including the keyword default and the statement to be executed.

Default keyword, in lowercase, ends with a full colon (:). The default part is actually optional but including it is a good practice for a programmer. After the statement for default part, you end the switch statement with the closing curly brace.

Now, let us work with a practical example. We are going to write a program that lets the user to enter a number between one and seven in a Java Option Pane. We’ll capture this user input in a String variable and later change it into an int variable.

We’ll then use a switch statement to output the day of the week corresponding to the number entered. We’ll use the following table of inputs and their corresponding outputs.

InputOutput

1

Sunday

2

Monday

3

Tuesday

4

Wednesday

5

Thursday

6

Friday

7

Saturday

Because we’ll use the Java Option Panes for inputs and outputs, include the following header statement for Java Option Panes like we did in our earlier lessons.

import javax.swing.JOptionPane;

Remember also to include the “main” part. Type the following code carefully inside the class. Pay attention to semi colons, full colons and curly braces. You can work with my variables or you can create your own. Notice that in the code below I have only done for inputs of numbers 1 to 3.

Java program using switch statement

programming-in-java-a-step-by-step-tutorial-for-beginners-lesson-9

Run your program, you should be able to get some outputs.

programming-in-java-a-step-by-step-tutorial-for-beginners-lesson-9
programming-in-java-a-step-by-step-tutorial-for-beginners-lesson-9
programming-in-java-a-step-by-step-tutorial-for-beginners-lesson-9
programming-in-java-a-step-by-step-tutorial-for-beginners-lesson-9

Exercise:

After your program has worked modify it to cater for numbers 1 to 7 inputs with appropriate outputs.

One thing about Java switch statement is that certain lower versions of Java do not support casing with String variables. If you try to use a switch statement with a String variable in a Java version that does not support strings you’ll get the following warning:

programming-in-java-a-step-by-step-tutorial-for-beginners-lesson-9

But suppose you wanted to use strings anyway? One way to do it is to let the program accept inputs as string and then assign those string to your own number (int) codes using IF .. ELSE IF statement. You can then use the int values in the switch statement. Sound confusing?

Suppose we want to write a program to allow the users to enter a color of their choice and output an appropriate message based on the color entered. We can do as shown in the following code:

Java program using switch statement

package myfirstprogram;
import javax.swing.JOptionPane;
public class MySwitch {
    public static void main(String[] args) {
        String color;
        int num;
        num = 0;
        color = JOptionPane.showInputDialog("Enter color of your choice:");
 
        if(color.equals("Red")){
            num = 1;
        }
        else if(color.equals("White")){
            num = 2;
        }
        switch(num){
        case 1: 
        JOptionPane.showMessageDialog( null, "Red is for love" );
        break;
       
        case 2: 
        JOptionPane.showMessageDialog( null, "White is for peace" );
        break;
        default:
        JOptionPane.showMessageDialog( null, "I don't recognize your color");
        }

    } 
}

Notice that in the above code I have used another Java method, equals().This method is used to check if one string is exactly equal to another. That means if the user entered white but we are checking for White (uppercase “W”) then those two strings are not equal. Run the program and you should be able to get the outputs.

programming-in-java-a-step-by-step-tutorial-for-beginners-lesson-9
programming-in-java-a-step-by-step-tutorial-for-beginners-lesson-9

Let us try with “red” i.e. with lowercase “r”

programming-in-java-a-step-by-step-tutorial-for-beginners-lesson-9
programming-in-java-a-step-by-step-tutorial-for-beginners-lesson-9

Now you got it, Red is NOT equal to red in Java’s equal() method. In the next lesson, we’ll look into FOR loop statement in Java.


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