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by Dinesh Thakur

When there is requirement of several branching i.e. if we need several if statements, it is better to use switch statement. In other words, switch is a variation of if statement which performs multiway branching.

Syntax:

 

switch (expression)

{

case value:

                      statement(s) ;

                      break;

case value:

                     statement(s);

                     break;

default:

                     statement(s);

                      break;

}

The keyword switch begins the switch construct. The parentheses contain expression which may be a byte, a char, a short, or an int. Next is a required {, followed by any number of constructs that begin with the keyword case and end with break, with any number of statements in between. Then, there is an optional keyword called default which ends with break. Finally, a required} completes the case statement.

The case statement works by evaluating the expression and then scanning down the case statements until a match is found. When the match is found, the corresponding group of statements between the case and break will be executed. break statement is for exiting from switch construct. If no matches are found and a default is present, the group of statements associated with default will be executed. If no default is present and no match is found control jumps to the statements following switch command.

Note: When the statement of any case is executed and we forget to place break, then control will go into following case construct and executes its statements also. It keeps on executing all the statements of each case construct one after the other until a break is encountered or switch gets over.

 

Example:

 

switch(k)

{

case 'a' :        System.out.println("Apple ");

                     break;

case 'b' :       System.out.println("Bat") ;

                     break;

default :       System.out.println("Please enter a character");

}

 

In above example, the control will jump to respective statement depending on the value of the variable k. If the value of k is 'a', then Apple will be printed on the screen. break after System.out.println takes the control out of the switch statement. If break is not included, control will also execute the case statement following it i.e. it will also print Bat, even though the value of k is 'a'. This means that when case is true, then its statements are executed followed by other case statements until control encounters break statement.

If the value of k is neither 'a' nor 'b', then control will execute default statement displaying "Please enter a character" on the screen.

Look at the following example: Here, we have removed all break statements

 

switch(k)

{

case 'a' : System.out.println("Apple");

case 'b' : System.out.println("Bat");

case 'c' : System.out.println("Cat");

default: System.out.println("Please enter a character");

}

 

In above example, if the value of k is 'a', it will print:

Apple

Bat

Cat

Please enter a character

This is because after p~inting Apple, control will continue executing another case

statement in absence of break statement

If value of k is 'b', it will print

Bat

Cat

Please enter a character

If value of k is 'c', it will print

Cat

Please enter a character

Features of the switch statement:

1. The switch differs from the if statements in the sense that switch can only test for equality, whereas if can evaluate any type of logical expression. That is, the switch looks only for a match between the value of the expression and one of its case constants.

2. No two case constants in the same switch can have identical values.

3. A switch statement is more efficient than a set of nested if statements.

When it compiles a switch statement, the Java compiler will inspect each of the case constants and create a "jump table" that it will use for selecting the path of execution depending on the value of the expression. It is for this reason that switches statement runs much faster than the sequence of if else.

To demonstrate the circumstances where switch performs better then the series of if statements, lets look at the following two programs. First program is written with the help of if statement and the same program is then written with switch statement

 

/* Enter a value between 1 and 4 and print it in words */

import java.io.*;

class SwitchExample

{

            public static void main(String args[] )

                throws IOException

            {

                        BufferedReader k=new BufferedReader(new InputStreamReader

                                    (System.in));

                        String h;

                        int n;

                        System.out.println("Enter a value between 1 and 4 ");

                        h=k.readLine( );

                        n=Integer.parseInt(h);

                        if(n==1)

                        {

                                    System.out.println("One");

                        }

                        if(n==2)

                        {

                                    System.out.println("Two");

                        }

                        if(n==3)

                        {

                                    System.out.println("Three");

                        }

                        if(n==4)

                        {

                                    System.out.println("Four");

                        }

            }

}

Now, the same above program is also done with switch statement for comparison

 

/* Enter a value between 1 & 4 and print it in words using switch command.  */

import java.io.*;

class SwitchExample

{

            public static void main(String args[] ) 

            throws IOException

            {

                        BufferedReader k=new BufferedReader(new InputStreamReader

                                    (System.in));

                        String h;

                        int n;

                        System.out.println("Enter a value between 1 and 4 ");

                        h=k.readLine( );

                        n=Integer.parseInt(h);

                        switch(n)

                        {

                                    case 1:

                                                System.out.println("One");

                                                break;

                                    case 2:

                                                System.out.println("Two");

                                                break;

                                    case 3:

                                                System.out.println("Three");

                                                break;

                                    case 4:

                                                System.out.println("Four");

                                                break;

                                    default :

                                                System.out.println("The value is above Four");

                        }

            }

}

From above two programs, we can easily see that using switch statement is more handy and readable as compared to using series of if statements