04f switch..case in Java

Learning Java

Custom Search

Home

01 Getting Started
02 Concepts
03 Variables & Data Types

04 Program Logic
     a Statements
     b Comments
     c Operators
     d Order of Operation
     e if
     f switch..case
     g for
     h while, do..while

05 Modifiers
06 GUI
07 Other Useful Classes
08 Handling Events
09 Handling Exceptions
10 Project 01 - Mortg Calc
11 More on Applets
12 Layout Manager
13 Project 02 - Calculator
14 Threads
15 Project 03 - Wake Up
16 File I/O
17 Project 04 - File I/O

Expanded Table of Contents
Debugging Hints
HTML Review
Download Samples

Previous Next

switch..case Statement

The "switch..case" construction allows us to test multiple values of an expression or a variable and perform different tasks depending on that value. This can be accomplished using the "if..else if" construction but can become a bit cumbersome. The format is similar to the following. The "default" keyword is used to point out what should be done if the above conditions are not met. The "default" is not required. The "break" keyword stops execution from falling through to the next statement.

	switch (expression) {
	    case value1:
		execute this step 1;
		execute this step 2;
		execute this step 3;
	 	break;
	    case value2:
		execute this step 4;
		execute this step 5;
		execute this step 6;
	 	break;
	    case value3:
		execute this step 7;
		execute this step 8;
		execute this step 9;
	 	break;
	    default:
		execute this step 10;
		execute this step 11;
		execute this step 12;
	}

The following "if..else" construction and "switch..case" construction do the same thing.

	int quarter = 2;

        if (quarter == 1) { 
	    System.out.println("Jan start project A"); 
	    System.out.println("Feb & Mar complete phase I");
	} else if (quarter == 2) { 
	    System.out.println("Apr & May get financing"); 
	    System.out.println("Jun start phase II"); 
	} else if (quarter == 3) { 
	    System.out.println("Jul & Aug finish phase II"); 
	    System.out.println("Sep start phase III"); 
	} else if (quarter == 4) { 
	    System.out.println("Oct & Nov finish phase III"); 
	    System.out.println("Dec start plan for next year");
	} else {  
	    System.out.println("Invalid quarter.");
        }

	int quarter = 2;

        switch (quarter) {
            case 1:  
		System.out.println("Jan start project A"); 
		System.out.println("Feb & Mar complete phase I");
		break;
            case 2:  
		System.out.println("Apr & May get financing"); 
		System.out.println("Jun start phase II"); 
		break;
            case 3:  
		System.out.println("Jul & Aug finish phase II"); 
		System.out.println("Sep start phase III"); 
		break;
            case 4:  
		System.out.println("Oct & Nov finish phase III"); 
		System.out.println("Dec start plan for next year");
		break;
            default: 
		System.out.println("Invalid quarter.");
        }

Notice in the following execution when the "break" keywords are commented out, all the statements below the true condition are executed.

class SwitchTest {

    public static void main(String args[]) {

	int quarter = 2;

        switch (quarter) {
            case 1:  
		System.out.println("Jan start project A"); 
		System.out.println("Feb & Mar complete phase I");
		//break;
            case 2:  
		System.out.println("Apr & May get financing"); 
		System.out.println("Jun start phase II"); 
		//break;
            case 3:  
		System.out.println("Jul & Aug finish phase II"); 
		System.out.println("Sep start phase III"); 
		//break;
            case 4:  
		System.out.println("Oct & Nov finish phase III"); 
		System.out.println("Dec start plan for next year");
		//break;
            default: 
		System.out.println("Invalid quarter.");
        }
    }
}

Previous Next

Steps In Learning