switch

• https://www.baeldung.com/java-switch
• http://docs.oracle.com/javase/tutorial/java/nutsandbolts/switch.html
• break statement
  • break is used to terminate the case, if it is not used then it goes to the next case and executes
  • break in last case is optional, but recommended for consistency
• Arguments
  • null is not allowed, it throws NullPointerException if it is null
  • The following are allowed
    • byte and Byte
    • short and Short
    • int and Integer
    • char and Character
    • enum
    • String
• case
  • constants are generally used
  • variables if used should be final
• comparison
  • For String, it uses equals() method

String result;
switch (animal) {
    case "DOG":
    case "CAT":
        result = "domestic animal";
        break;
    case "TIGER":
        result = "wild animal";
        break;
    default:
        result = "unknown animal";
        break;
}

Switch Expression

• Introduced in Java 14+
• There is no break statement and hence it does not fall through cases

var result = switch(month) {
    case JANUARY, JUNE, JULY -> 3;
    case FEBRUARY, SEPTEMBER, OCTOBER, NOVEMBER, DECEMBER -> 1;
    case MARCH, MAY, APRIL, AUGUST -> 2;
    default -> 0; 
};

• Use yield to return the data

var result = switch (month) {
    case JANUARY, JUNE, JULY -> 3;
    case FEBRUARY, SEPTEMBER, OCTOBER, NOVEMBER, DECEMBER -> 1;
    case MARCH, MAY, APRIL, AUGUST -> {
        int monthLength = month.toString().length();
        yield monthLength * 4;
    }
    default -> 0;
};

• return can be used but then you should not store the data in result

private static int test(Month month) {
    switch (month) {
        case JANUARY, JUNE, JULY -> { return 3; }  // returns from the test()
        default -> { return 0; }
    }
}
 
// This is wrong!!!
private static int test(Month month) {
    var result = switch (month) {  // compilation error cannot store or return
        case JANUARY, JUNE, JULY -> { return 3; }
        default -> { return 0; }
    }
    return result;
}

• Switch statements are not exhaustive, but switch expressions must be exhaustive as per compiler

Pattern matching

• Introduced in Java 21+
• Available for switch statements and expressions
• Type checks can be added which internally uses instanceof
• Guarded Patterns can be used using when keyword
• null case can be added to avoid NullPointerException

static double getDoubleUsingSwitch(Object o) {
    return switch (o) {
        // Type matching
        case Integer i -> i.doubleValue(); 
        case Float f -> f.doubleValue();
        // Type matching with Guarded case
        case String s when s.length() > 0 -> Double.parseDouble(s); 
        // null case
        case null -> 0d;
        // default case
        default -> 0d;
    };
}