@Size for length constraints in Spring Boot - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ component_behavior

intermediate

What happens when a string field annotated with @Size(min=5, max=10) receives a 3-character input?

Consider a Spring Boot entity with a field annotated as @Size(min=5, max=10). What will be the validation result if the input string length is 3?

Spring Boot

public class User {
    @Size(min=5, max=10)
    private String username;

    // getters and setters
}

A Validation fails because the input length is less than the minimum size.

B Validation fails because the input length is greater than the maximum size.

C Validation passes because the input is a string regardless of length.

D Validation passes because @Size only checks maximum length.

💡 Hint

Remember that @Size checks both minimum and maximum length constraints.

The @Size annotation enforces that the string length must be between the specified min and max values inclusive. Since the input length is 3, which is less than the minimum 5, validation fails.

📝 Syntax

intermediate

Which @Size annotation usage is syntactically correct for a list field in Spring Boot?

You want to validate a list to have between 2 and 5 elements using @Size. Which option is correct?

Spring Boot

public class Group {
    @Size(???)
    private List<String> members;
}

A @Size(min=2, max=5)

B @Size(2, 5)

C @Size(minLength=2, maxLength=5)

D @Size(length=2..5)

💡 Hint

Check the official @Size annotation parameters for min and max.

The @Size annotation uses named parameters min and max to specify length constraints. The correct syntax is @Size(min=2, max=5).

🔧 Debug

advanced

Why does this @Size annotation not enforce the maximum length?

Given the code below, why does the validation allow strings longer than 10 characters?

Spring Boot

public class Product {
    @Size(min=3)
    private String code;

    // getters and setters
}

A Because the field is private and not accessible for validation.

B Because min attribute is ignored for strings.

C Because @Size only works on collections, not strings.

D Because max attribute is missing, so no maximum length is enforced.

💡 Hint

Check if both min and max are specified to enforce length limits.

The @Size annotation enforces minimum and maximum length only if both min and max are set. If max is missing, there is no upper limit.

❓ state_output

advanced

What is the validation result for a null string annotated with @Size(min=1, max=5)?

If a string field is annotated with @Size(min=1, max=5) and the input value is null, what happens during validation?

Spring Boot

public class Item {
    @Size(min=1, max=5)
    private String label;

    // getters and setters
}

A Validation passes only if @NotNull is also present.

B Validation passes because @Size ignores null values.

C Validation throws NullPointerException.

D Validation fails because null length is less than min.

💡 Hint

Think about how @Size treats null values by default.

The @Size annotation does not consider null values invalid. Null is allowed unless combined with @NotNull.

🧠 Conceptual

expert

How does @Size behave differently on a String vs a Collection in Spring Boot validation?

Which statement correctly describes the difference in how @Size validates Strings and Collections?

A @Size only works on Strings, Collections are validated by @Length.

B @Size validates the byte size of Strings and the memory size of Collections.

C @Size checks the length of a String and the number of elements in a Collection.

D @Size requires separate annotations for Strings and Collections.

💡 Hint

Think about what length means for strings and collections.

@Size counts characters in Strings and counts elements in Collections to enforce min and max constraints.