Switch statement in Java - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of switch with pattern matching

What is the output of the following Java code using switch with pattern matching?

Java

Object obj = 123;
String result = switch (obj) {
    case Integer i -> "Integer: " + i;
    case String s -> "String: " + s;
    default -> "Unknown";
};
System.out.println(result);

A String: 123

B Integer: 123

C Unknown

D Compilation error

💡 Hint

Remember that the switch matches the first compatible case.

The object is an Integer with value 123, so the case Integer i matches and returns "Integer: 123".

❓ Predict Output

intermediate

Switch expression with yield

What will be printed by this Java code using switch expression with yield?

Java

int day = 3;
String dayName = switch (day) {
    case 1 -> "Monday";
    case 2 -> "Tuesday";
    case 3 -> {
        yield "Wednesday";
    }
    default -> "Invalid";
};
System.out.println(dayName);

A Wednesday

B Invalid

C Compilation error

D null

💡 Hint

The yield keyword returns a value from a block in a switch expression.

For day = 3, the switch block uses yield to return "Wednesday".

❓ Predict Output

advanced

Switch with multiple labels and fall-through

What is the output of this Java switch statement?

Java

int num = 2;
switch (num) {
    case 1, 2, 3:
        System.out.print("Low");
    case 4:
        System.out.print(" Medium");
        break;
    default:
        System.out.print(" High");
}

A Low

B Medium

C Low Medium

D Low Medium High

💡 Hint

Without break after case 1,2,3, execution falls through to case 4.

Case 2 matches, prints "Low", then falls through to case 4, prints " Medium", then breaks.

❓ Predict Output

advanced

Switch expression with sealed classes

Given sealed classes and a switch expression, what is the output?

Java

sealed interface Shape permits Circle, Square {}
record Circle(double radius) implements Shape {}
record Square(double side) implements Shape {}

Shape shape = new Circle(2.0);
String desc = switch (shape) {
    case Circle c -> "Circle with radius " + c.radius();
    case Square s -> "Square with side " + s.side();
};
System.out.println(desc);

A Compilation error due to missing default

B Square with side 2.0

C Runtime exception

D Circle with radius 2.0

💡 Hint

Sealed interfaces allow exhaustive switch without default.

The shape is a Circle with radius 2.0, so the first case matches and returns the description.

❓ Predict Output

expert

Switch expression with null and pattern matching

What happens when this Java code runs?

Java

Object obj = null;
String result = switch (obj) {
    case String s -> "String: " + s;
    case null -> "Null value";
    default -> "Other";
};
System.out.println(result);

A Compilation error: 'case null' not allowed

B Other

C Null value

D Runtime NullPointerException

💡 Hint

Java switch does not allow 'case null' labels.

Java switch expressions do not support 'case null' labels, so this code does not compile.

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