Switch statement in Java - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a switch statement used for in Java?

A switch statement lets you choose between many options based on the value of a variable. It helps make decisions by matching the variable to different cases.

beginner

How do you write a basic switch statement in Java?

You write switch(variable) { case value1: //code break; case value2: //code break; default: //code }. The variable is checked against each case value, and the matching case runs.

intermediate

What happens if you forget to put break; in a switch case?

Without break;, Java continues running the next cases even if they don't match. This is called "fall-through" and can cause unexpected results.

intermediate

Can a switch statement handle strings in Java?

Yes! Since Java 7, switch statements can use strings as the variable to compare against case values.

beginner

What is the purpose of the default case in a switch statement?

The default case runs if none of the other cases match. It's like an 'else' to catch all other values.

What keyword stops execution from falling through to the next case in a switch statement?

A break

B continue

C stop

D exit

The break keyword stops the switch from running the next cases after a match.

Which of these types can be used in a switch statement in Java?

A int, String, enum

B double, float, long

C boolean, char, byte

D Object, Array, List

Switch supports int, String, and enum types, but not floating-point types or complex objects.

What happens if no case matches and there is no default case?

A It runs the first case anyway

B The program crashes

C It asks the user for input

D The switch does nothing and moves on

If no case matches and no default is provided, the switch block is skipped.

Which Java version introduced support for String in switch statements?

A Java 5

B Java 8

C Java 7

D Java 6

Java 7 added the ability to use Strings in switch statements.

What is the role of the case keyword in a switch statement?

A Ends the switch statement

B Defines a possible value to match

C Declares a variable

D Starts a loop

case defines a value that the switch variable is compared against.

Explain how a switch statement works and why you might use it instead of multiple if-else statements.

Think about choosing between many options based on one value.

Describe what happens if you omit the break statement in a switch case and give an example of when this might be useful.

Sometimes you want multiple cases to run the same code.

Practice

1. What is the main purpose of a switch statement in Java?

easy

A. To repeat a block of code multiple times

B. To select one action from many based on a value

C. To define a new class

D. To handle errors and exceptions

Solution

1. Step 1: Understand the role of switch

   The switch statement chooses one path from many based on a value.

2. Step 2: Compare with other options

   Loops repeat code, classes define objects, and exceptions handle errors, so they don't match.

3. Final Answer:

   To select one action from many based on a value -> Option B

4. Quick Check:

   Switch = Select action based on value [OK]

Hint: Switch picks one case based on value, like a menu choice [OK]

Common Mistakes:

• Confusing switch with loops
• Thinking switch handles errors
• Mixing switch with class definitions

2. Which of the following is the correct syntax to start a switch statement in Java?

easy

A. switch (variable) { ... }

B. switch variable { ... }

C. switch [variable] { ... }

D. switch variable() { ... }

Solution

1. Step 1: Recall switch syntax

   The correct syntax uses parentheses around the variable: switch (variable) { ... }.

2. Step 2: Check other options

   Options A, B, and D miss parentheses or use wrong brackets, causing syntax errors.

3. Final Answer:

   switch (variable) { ... } -> Option A

4. Quick Check:

   Switch needs parentheses around variable [OK]

Hint: Switch always uses parentheses around the variable [OK]

Common Mistakes:

• Omitting parentheses
• Using square brackets instead of parentheses
• Adding parentheses after variable name

3. What will be the output of this Java code?

int day = 3;
switch (day) {
  case 1: System.out.println("Monday"); break;
  case 2: System.out.println("Tuesday"); break;
  case 3: System.out.println("Wednesday"); break;
  default: System.out.println("Invalid day");
}

medium

A. Wednesday

B. Tuesday

C. Invalid day

D. Monday

Solution

1. Step 1: Identify the value of day

   The variable day is set to 3.

2. Step 2: Match the case in switch

   Case 3 matches, so it prints "Wednesday" and then breaks out of the switch.

3. Final Answer:

   Wednesday -> Option A

4. Quick Check:

   day=3 matches case 3 = Wednesday [OK]

Hint: Match variable value to case label to find output [OK]

Common Mistakes:

• Forgetting break causes fall-through
• Choosing default when case matches
• Mixing case numbers and output strings

4. Identify the error in this switch statement:

int num = 2;
switch (num) {
  case 1:
    System.out.println("One");
  case 2:
    System.out.println("Two");
    break;
  default:
    System.out.println("Other");
}

medium

A. case labels must be strings

B. Missing default case

C. Switch variable must be a String

D. Missing break after case 1

Solution

1. Step 1: Check breaks in cases

   Case 1 lacks a break, so execution falls through to case 2.

2. Step 2: Understand effect of missing break

   Without break, both "One" and "Two" print when num=1, which may be unintended.

3. Final Answer:

   Missing break after case 1 -> Option D

4. Quick Check:

   Each case needs break to stop fall-through [OK]

Hint: Always add break after each case unless fall-through wanted [OK]

Common Mistakes:

• Forgetting break causes multiple prints
• Thinking default is mandatory
• Believing switch only works with strings

5. You want to write a switch statement that prints "Weekend" for days 6 and 7, "Weekday" for days 1 to 5, and "Invalid" otherwise. Which code correctly implements this?

hard

A. switch(day) {
case 1,2,3,4,5: System.out.println("Weekday"); break;
case 6,7: System.out.println("Weekend"); break;
default: System.out.println("Invalid");
}

B. switch(day) {
case 1 || 2 || 3 || 4 || 5:
System.out.println("Weekday"); break;
case 6 || 7:
System.out.println("Weekend"); break;
default:
System.out.println("Invalid");
}

C. switch(day) {
case 1: case 2: case 3: case 4: case 5:
System.out.println("Weekday"); break;
case 6: case 7:
System.out.println("Weekend"); break;
default:
System.out.println("Invalid");
}

D. switch(day) {
case (1,2,3,4,5):
System.out.println("Weekday"); break;
case (6,7):
System.out.println("Weekend"); break;
default:
System.out.println("Invalid");
}

Solution

1. Step 1: Understand Java switch syntax for multiple cases

   Java allows multiple case labels by stacking them without commas, like case 1: case 2:.

2. Step 2: Check each option's syntax

   switch(day) { case 1: case 2: case 3: case 4: case 5: System.out.println("Weekday"); break; case 6: case 7: System.out.println("Weekend"); break; default: System.out.println("Invalid"); } correctly stacks cases. switch(day) { case 1,2,3,4,5: System.out.println("Weekday"); break; case 6,7: System.out.println("Weekend"); break; default: System.out.println("Invalid"); } uses commas (invalid), C uses || (invalid), D uses parentheses (invalid).

3. Final Answer:

   switch(day) { case 1: case 2: case 3: case 4: case 5: System.out.println("Weekday"); break; case 6: case 7: System.out.println("Weekend"); break; default: System.out.println("Invalid"); } -> Option C

4. Quick Check:

   Stack multiple cases by repeating case lines [OK]

Hint: Stack multiple cases by repeating case lines without commas [OK]

Common Mistakes:

• Using commas between case labels
• Using logical OR (||) in case labels
• Using parentheses around case labels