'switch' Statement

The second of Java’s selection statements is the switch. The switch provides for a multiway branch. Thus, it enables a program to select among several alternatives.

NOTE

Although a series of nested if statements can perform multiway tests, for many situations the switch is a more efficient approach.

The traditional switch works like this:

• the value of an expression is successively tested against a list of constants.

• When a match is found, the statement sequence associated with that match is executed.

• Duplicate case values are not allowed.

• The type of each value must be compatible with the type of expression.

• The default statement sequence is executed if no case constant matches the expression.

• Execution will continue into the next case if no break statement is present.

• The default is optional,

• You can have empty cases.

switch(expression) 
{
	case constant1:
		statement sequence
		break;
	case constant2:
		statement sequence
		break;
	case constant3:
		statement sequence
		break;
.
.
	default:
		statement sequence
}

INFO

Today, expression can also be of type String.

For versions of Java prior to JDK 7, the expression controlling the switch must resolve to type byte, short, int, char, or an enumeration.

// Demonstrate the switch.
class SwitchDemo 
{
	public static void main(String[] args) 
	{
		int i;
		for(i=0; i<10; i++)
			switch(i) 
			{
				case 0:
					System.out.println("i is zero");
					break;
				case 1:
					System.out.println("i is one");
					break;
				case 2:
					System.out.println("i is two");
					break;
				case 3:
					System.out.println("i is three");
					break;
				case 4:
					System.out.println("i is four");
					break;
				default:
					System.out.println("i is five or more");
				}
	}
}

[!To note] switch(i) is given as a single line of code below the for loop but switch has its own block.

Switch Expressions

Introducing the Arrow in a case Statement

Easier way to supply a value is through the use of a new form of the case that substitutes -> for the : colon in a case.

case 'X': // ...

case 'X' -> // ...

arrow case and the traditional colon case.

Although both forms will match the character X, the precise action of each style of case statement differs in three very important ways.

• *First, one arrow case does not fall through to the next case. Thus, there is no need to use break. Execution simply terminates at the end of an arrow case.

• Second, the arrow case provides a “shorthand” way to supply a value when used in a switch expression. For this reason, the arrow case is often used in switch expressions.

• Third, the target of an arrow case must be either an expression, a block, or throw an exception. It cannot be a statement sequence, as is allowed with a traditional case.

case constant -> expression;

case constant -> { block-of-statements }

case constant -> throw …

IMPORTANT

When the target of an arrow case is an expression, the value of that expression becomes the value of the switch when that case is matched. As such, it provides a very efficient alternative to the yield statement in many situations.

case 1774, 8708, 6709 -> ShipMethod.TRUCK;

value of the expression (which is ShipMethod.TRUCK) automatically becomes the value produced by the switch when this case is matched. In other words, the expression becomes the value yielded by the switch.

---