Quick Answer
The answer is "String of length 5". This is correct because the switch expression employs pattern matching with type patterns, introduced in Java 17, which allows the switch to evaluate the runtime type of the object rather than just its value. Since obj is a String, the first case matches, binding the value to the variable s and executing the expression that concatenates "String of length " with s.length(), which returns 5 for "Hello". On the Oracle Certified Professional Java SE 17 Developer 1Z0-829 exam, this question tests your understanding of how type patterns in switch work with pattern matching, a key feature that replaces older instanceof-and-cast idioms. A common trap is forgetting that the type pattern only matches if the runtime type is exactly compatible—not if it's a parent type—so the default case would only fire if no type pattern matches. Memory tip: think of type patterns as "match and bind in one step"—the pattern both checks the type and assigns the variable, so you never need a separate cast.
This 1Z0-829 practice question tests your understanding of controlling program flow. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Given: Object obj = "Hello"; String result = switch(obj) { case String s -> "String of length " + s.length(); case Integer i -> "Integer"; default -> "Unknown"; }; What is result?
"Unknown"
Why wrong: Incorrect; the String case matches.
Compilation error
Why wrong: Incorrect; the switch expression is valid.
"String of length 5"
Correct: the String pattern matches and length is 5.
"Integer"
Why wrong: Incorrect; obj is not an Integer.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
"String of length 5"
The switch expression uses pattern matching with type patterns. The runtime type of obj is String, so the first case matches, binding the value to s and executing the expression "String of length " + s.length(). Since s is "Hello", s.length() returns 5, so result is "String of length 5". Option C is correct.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
"Unknown"
Why it's wrong here
Incorrect; the String case matches.
Compilation error
Why it's wrong here
Incorrect; the switch expression is valid.
"String of length 5"
Why this is correct
Correct: the String pattern matches and length is 5.
Related concept
Read the scenario before looking for a memorised answer.
"Integer"
Why it's wrong here
Incorrect; obj is not an Integer.
Common exam traps
The trap here is that candidates may think the switch requires a constant expression or that pattern matching is not allowed, leading them to expect a compilation error, or they may forget that the String case matches the runtime type, not the compile-time type of the reference.
Detailed technical explanation
Pattern matching for switch (JEP 406, 420, 427) allows type patterns in case labels, which perform a type check and binding in one step. The switch expression must be exhaustive; here the default clause ensures all possible types are covered. Under the hood, the compiler generates a type-checking cascade similar to instanceof, but with improved readability and safety.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A small business has 20 workstations on the 192.168.1.0/24 network and one public IP from its ISP. The router uses PAT (NAT overload) so all 20 devices share one public address using different source ports. NAT questions test whether you understand the four address terms and which direction each translation applies.
What to study next
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FAQ
Controlling Program Flow — This question tests Controlling Program Flow — Read the scenario before looking for a memorised answer..
The correct answer is: "String of length 5" — The switch expression uses pattern matching with type patterns. The runtime type of obj is String, so the first case matches, binding the value to s and executing the expression "String of length " + s.length(). Since s is "Hello", s.length() returns 5, so result is "String of length 5". Option C is correct.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
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