The Switch Statement

When the nature of the decision you need to make is a bit on the fuzzy side, it could be impractical to use the if-statement, for those kinds of decisions, you will use the switch-statement.

The syntax of the switch statement is;

switch(expression) {
  case CONSTANTEXPR:
  case ENUMCONSTANTNAME:
  default:
}

Where expression can either be a char, byte, short, int OR Character, Byte, Short, Integer OR an enum type. By the way, Character is not the same as char, that wasn't a typo. Character is a Java class which is a wrapper class for the char primitive.

Let's take a look at some sample code. The SwitchSample.java code extracts the Day of Week value from a Java Calendar object. The Day of Week is returned as integer, which makes it perfect to filter using a Switch statement rather than nested ifs

import java.util.Calendar;

class SwitchSample {

    public static void main(String args[]){

        Calendar now = Calendar.getInstance();
        int dow = now.get(Calendar.DAY_OF_WEEK);

        switch(dow) {
            case 0:
                System.out.println("Sunday");
                break;
            case 1:
                System.out.println("Monday");
                break;
            case 2:
                System.out.println("Tuesday");
                break;
            case 3:
                System.out.println("Wednesday");
                break;
            case 4:
                System.out.println("Thursday");
                break;
            case 5:
                System.out.println("Friday");
                break;
            case 6:
                System.out.println("Saturday");
                break;
            default:
                System.out.println("What the value really is = " + dow);
            }
        }
}

The switch is really simple to use, just put the expression which you'd like to test as an argument to the switch statement, then have a series of case statements inside the switch body.

Each case statement corresponds to a value, if the value of the expression is equivalent to a case value, then instructions immediately right after the colon of the case statement will be executed/evaluated, in fact the rest of the statements will be evaluated, all the way down, until it gets to the last instruction at the bottom of the switch statement; that's not what your intention might be; that is the reason why I put a break statement. Once a case statement evaluates to true, Java blindly executes all the statements after that case, it won't even bother checking the other cases -- so note this, and be careful.

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Senior IT Lecturer

Far Eastern University

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