Switch Statement

[stormswimmer]

Can someone please explain to me how to do a proper Switch Statement
Thanx
--Stormswimmer

[destin]

/** generate a number from 1 to 12 */
int rnd = ( int ) ( Math.random * 12 ) + 1;

int num = 0;

/** start switch statement */
switch( rnd ) { // if (rnd == ...
case 0: // 0)
    num = 5;
    /** fall though (no break statement) */
case 1: // 1)
    num += 3;
    break;
case 2: // 2 ||
case 3: // 3 ||
case 4: // 4)
    num = 10;
    break;
default: // else
    num = -5;
    break;
}

they only accept an int or a char. they are very similar to if statements.. the code above is the same as:

/** generate a number from 1 to 12 */
int rnd = ( int ) ( Math.random * 12 ) + 1;

int num = 0;

if ( rnd == 0 ) {
    num = 5;
    num += 3;
} else if ( rnd == 1 ) {
    num += 3;
} else if (( rnd == 2 ) || ( rnd == 3 ) || ( rnd == 4 )) {
    num = 10;
} else {
    num = -5;
}

i feel more organized using a switch statement, but you can only use switch statements with ints or chars so if your dealing with Objects, you have to use if statements.

[stormswimmer]

How do you write it? What are the cases and when do you use them?

[stormswimmer]

What is going on here

public class SwitchDemo {
    public static void main(String[] args) {

        int month = 8;
        switch (month) {
            case 1:  System.out.println("January"); break;
            case 2:  System.out.println("February"); break;
            case 3:  System.out.println("March"); break;
            case 4:  System.out.println("April"); break;
            case 5:  System.out.println("May"); break;
            case 6:  System.out.println("June"); break;
            case 7:  System.out.println("July"); break;
            case 8:  System.out.println("August"); break;
            case 9:  System.out.println("September"); break;
            case 10: System.out.println("October"); break;
            case 11: System.out.println("November"); break;
            case 12: System.out.println("December"); break;
            default: System.out.println("Not a month!");break;
        }
    }
}

[destin]

checks to see what month is equal:

public class SwitchDemo {
    public static void main(String[] args) {

        int month = 8;
        switch (month) {
            // if (month == 1) System.out.println("January");
            case 1:  System.out.println("January"); break;
            // else if (month == 1) System.out.println("Febuary");
            case 2:  System.out.println("February"); break;
            // ...etc.
            case 3:  System.out.println("March"); break;
            case 4:  System.out.println("April"); break;
            case 5:  System.out.println("May"); break;
            case 6:  System.out.println("June"); break;
            case 7:  System.out.println("July"); break;
            case 8:  System.out.println("August"); break;
            case 9:  System.out.println("September"); break;
            case 10: System.out.println("October"); break;
            case 11: System.out.println("November"); break;
            case 12: System.out.println("December"); break;
            // else System.out.println("Not a month!");
            default: System.out.println("Not a month!");break;
        }
    }
}

So since month is equal to 8, "August" will be printed.
If month was 12, "December" would be printed.
if month was 15, "Not a month!" would be printed.

[srekcus]

You don't need to do anything special to execute a switch, it's an alternative to using an if/else statement.

Here's a simple example ...

int num = 3;
switch(num){
     case 1: System.out.println("num = 1!"); break;
     case 2: System.out.println("num = 2!"); break;
     case 3: System.out.println("num = 3!"); break;
     default: System.out.println("num is unknown");
}

The switch function determines what to do depending on the value of a variable.

The case value is saying if the input variable is equal to this, then execute the following code. Break tells the program to exit the switch statement. Default is executed if no case was found to be true.

Switches are not limited to integers, this is valid too:

char letter = 'A';
switch(letter){
     case 'A': System.out.println("You typed A"); break;
     case 'B': System.out.println("You typed B"); break;
     case 'C': System.out.println("You typed C"); break;
     default: System.out.println("I don't know my ABC's");
}

The above code is exactly the same as if you entered the following if/else statement, it's just a matter of preference.

char letter = 'A';
if(letter == 'A'){
     System.out.println("You typed A");
} else if (letter == 'B'){
     System.out.println("You typed B");
} else if (letter == 'C'){
     System.out.println("You typed C");
} else {
     System.out.println("I don't know my ABC's");
}

[destin]

You don't need to do anything special to execute a switch, it's an alternative to using an if/else statement.

if-else statements resolve to booleans, therefore you can put anything in there that will resolve to a boolean (ie. a method that returns a boolean). You can use it alternatively, but only if you are dealing with ints (/chars).

Switches are not limited to integers, this is valid too:

well.. characters and integers are really the samething..

System.out.println((int) 'h' );

will print:
104

just as

System.out.println((char) 104 );

will print:
h

i don't mean to be annoying srekcus, i just want to make sure stormswimmer thoroughly undestands the concept

[nspils]

You can also use Enums to be the value which is compared in a switch structure.