Quick Answer
The answer is Hello. This is correct because String objects in Java are immutable, meaning once a String is created, its value cannot be changed. When you call concat() on a String, it does not modify the original object; instead, it creates and returns a brand new String containing the concatenated result. Since the code calls str.concat("World") without assigning the returned value back to str, the original str variable still points to "Hello", and that is what prints. On the Oracle Java Foundations 1Z0-811 exam, this question tests your understanding of String immutability and concat behavior—a classic trap where students assume concat() alters the original string. The exam often uses this pattern to check whether you remember that methods on immutable objects return new objects rather than modifying the existing one. Memory tip: think of concat() as a "copy-and-join" operation—it leaves the original untouched and hands you a new string, so if you want the change, you must catch it with an assignment.
This 1Z0-811 practice question tests your understanding of primitives, strings and operators. 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.
public class StringTest {
public static void main(String[] args) {
String s = "Hello";
s.concat(" World");
System.out.println(s);
}
}Refer to the exhibit. What is the output?
public class StringTest {
public static void main(String[] args) {
String s = "Hello";
s.concat(" World");
System.out.println(s);
}
}HelloWorld
Why wrong: No concatenation performed.
Hello World
Why wrong: concat does not modify original.
Compilation error
Why wrong: Code compiles fine.
Hello
String is immutable, s unchanged.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
Hello
The code prints 'Hello' because the `String` variable `str` is assigned the value `"Hello"` and then `str.concat("World")` is called. However, `String` objects are immutable in Java, so `concat()` returns a new string without modifying the original `str`. Since the result of `concat()` is not assigned back to `str`, the original `str` remains `"Hello"`, and `System.out.println(str)` outputs `Hello`.
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.
HelloWorld
Why it's wrong here
No concatenation performed.
Hello World
Why it's wrong here
concat does not modify original.
Compilation error
Why it's wrong here
Code compiles fine.
Hello
Why this is correct
String is immutable, s unchanged.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Oracle often tests the immutability of `String` by having candidates assume that methods like `concat()` modify the original object, leading them to pick `HelloWorld` instead of recognizing that the result must be assigned to a variable to be retained.
Detailed technical explanation
In Java, `String` objects are immutable, meaning any method like `concat()`, `toUpperCase()`, or `replace()` returns a new `String` instance rather than altering the original. This immutability is enforced by the `final` class and internal `char[]` array that is not exposed. A common real-world scenario is building strings in loops; using `concat()` repeatedly creates many intermediate objects, which is why `StringBuilder` or `StringBuffer` is preferred for mutable string operations.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A practitioner preparing for the 1Z0-811 exam encounters this exact type of scenario on the job. The correct answer here is not the most general option — it is the best answer for the specific constraint described. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Real exam questions reward reading the full scenario before eliminating options, because the constraint defines which answer fits.
What to study next
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FAQ
Primitives, Strings and Operators — This question tests Primitives, Strings and Operators — Read the scenario before looking for a memorised answer..
The correct answer is: Hello — The code prints 'Hello' because the `String` variable `str` is assigned the value `"Hello"` and then `str.concat("World")` is called. However, `String` objects are immutable in Java, so `concat()` returns a new string without modifying the original `str`. Since the result of `concat()` is not assigned back to `str`, the original `str` remains `"Hello"`, and `System.out.println(str)` outputs `Hello`.
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 30, 2026
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