by Dinesh Thakur

The switch statement is a multi-way decision making statement which selects one of several alternatives based on the value of an integer variable or expression. The switch statement is mainly used to replace multiple if-else-if statement. The if-else-if statement causes performance degradation as several conditions need to be evaluated before a particular condition is satisfied.

 

Its syntax is

 

switch (expression)

{

case constant l statement(s)1; [break ;]

case constant 2 statement(s)2;[break;]

……………………………………………………

case constant n : statement(s)n;[break ;]

default statement(s);

}

 

This structure starts with a keyword switch followed by the expression enclosed in the parentheses. The expression can result in a constant value of type char, byte, short ,int or an enumeration constant but not of type long, float or double. Possible switch options are defined by one or more case values also known as case labels. A case label consists of the case keyword followed by a constant value i.e. the value which will select the case, followed by a colon. Each case label must be of the same data type as that of the switch expression. The value of the expression is compared with each of the case labels (integer/character constants) in the order they appear in the switch statement. If a match occurs then the statement(s) corresponding to that case are executed. If no match occurs with any of the case then only the statement(s) following the default case are executed. The default part is optional in the switch statement.

 

Each case can contain zero, one or more program statements. Unlike other control structures the block of statements corresponding to a case are not required to be enclosed in curly braces.

 

A case is normally terminated with a break statement. When a break statement is encountered, the switch statement is exited and program continues with the next executable statement following the switch statement. In some situations, a case may not be terminated with a break statement then the statements for the next case in the sequence will be executed as well as through to the other statements until another break statement is found or end of the switch statement is reached. The last case statement need not have a break statement as the program control automatically transfers out of the switch statement.

/* Enter a character between a and d and print its corresponding word using switch command. that is, print Apple if a is entered, Bat if b is entered and so on. */

 

import java.io.*;

class NestedSwitchStatements

{

            public static void main(String args[] ) 

            throws IOException

            {

                        BufferedReader k=new BufferedReader(new InputStreamReader

                                    (System.in));

                        char h;

                        System.out.print("Enter a character between a and d : ");

                        h=(char)k.read();

                        switch (h)

                        {

                                    case 'a' :

                                    case 'A':

                                                System.out.println("Apple");

                                                break;

                                    case 'b' :

                                    case 'B':

                                                System.out.println("Bat");

                                                break;

                                    case 'c' :

                                    case 'C':

                                                System.out.println("Cat");

                                                break;

                                    case 'd' :

                                    case 'D':

                                                System.out.println("Dog");

                                                break;

                                    default :

                                              System.out.println("Value out of range. Please enter between a and d");

 

                        }

            }

}

 

/* Enter a month and year and display the number of days in that month. Use switch statement. */

 

import java.io.*;

class SwitchStatements

{

            public static void main(String args[] ) 

            throws IOException

            {

                        BufferedReader k=new BufferedReader(new InputStreamReader

                                    (System.in));

                        String h;

                        int m,y,nod;

                        System.out.println("Enter month number : 1 for Jan, 2 for Feb       ...");

                        h=k.readLine( );

                        m=Integer.parseInt(h);

                        System.out.println("Enter year");

                        h=k.readLine( );

                        y=Integer.parseInt(h);

                        nod=0;

                        switch (m)

                        {

                                    case 1:

                                    case 3:

                                    case 5:

                                    case 7:

                                    case 8:

                                    case 10:

                                    case 12:

                                                nod =31;

                                                break;

                                    case 4:

                                    case 6:

                                    case 9:

                                    case 11:

                                                nod =30;

                                                break;

                                    case 2:

                                                if (((y % 4 == 0) && !(y % 100 == 0)) || (y % 400 == 0) )

                                                nod = 29;

                                                else

                                                nod = 28;

                                                break;

                                    default:

                                                nod = 0;

                                                break;

                        }

 

                        System.out.println("Number of days in ths month are " +nod);

            }

}