switch on an enum

What you will learn

• Switch on an enum with simple constant names as case labels
• Write exhaustive switch expressions over an enum without default
• Explain how a default branch hides new constants
• Avoid the NullPointerException from switching on a null enum

Topics in this lesson

1. case labels use the constant's simple name
2. A switch expression must cover every constant
3. A default branch hides new constants
4. Switching on a null enum

Key points

• In switch (mode), each label is the simple constant name: case UPI, not case PaymentMode.UPI.
• A switch expression that lists every constant needs no default, and javac flags any constant that is missing.
• A default branch silently handles constants added later; leave it out of enum switches.
• Switching on a null enum throws NullPointerException, even with a default.

Interview questions this lesson answers

• Why are the case labels in an enum switch written without the enum name?
• Do you need a default in a switch expression over an enum?
• What is risky about a default branch when switching on an enum?
• What happens if the enum variable in a switch is null?
• Must a switch statement on an enum cover every constant?
• You add a constant to an enum used all over a large project. How do you find every place that must handle it?