1Z0-811 · topic practice
Practise Oracle Java Foundations 1Z0-811 Java Basics and Syntax practice questions — original exam-style scenarios with answer choices, explanations, and analysis of common mistakes.
Courseiva uses original exam-style practice questions designed for learning and revision. The goal is to understand the concepts, recognise exam patterns, and improve through explanations — not memorise copied exam dumps.
What the exam tests
Java Basics and Syntax questions test whether you can apply the concept in context, not just recognise a definition.
How the topic appears in realistic exam-style scenarios.
Which detail in the question changes the correct answer.
How to eliminate plausible but wrong options.
How to connect the question back to the wider exam objective.
Watch out for
Practice set
19 questions · select your answer, then reveal the explanation
Trap 1: Compilation error
Code compiles fine.
Trap 2: 6
This would be the result of ++x.
Trap 3: Runtime exception
No exception occurs.
Compilation error
Why wrong: Code compiles fine.
5
x++ returns 5, then x becomes 6.
6
Why wrong: This would be the result of ++x.
Runtime exception
Why wrong: No exception occurs.
Trap 1: It must have a main method to compile.
Compilation does not require main.
Trap 2: It can contain multiple public classes.
Only one public class per file.
Trap 3: The public class name can differ from the file name.
Must match.
It must have a main method to compile.
Why wrong: Compilation does not require main.
It can contain multiple public classes.
Why wrong: Only one public class per file.
It can contain exactly one public class with the same name as the file.
This is the standard rule.
The public class name can differ from the file name.
Why wrong: Must match.
Trap 1: Runtime error
No runtime error.
Trap 2: Compilation error
Code compiles.
Trap 3: Equal
== compares references, not content.
Runtime error
Why wrong: No runtime error.
Compilation error
Why wrong: Code compiles.
Equal
Why wrong: == compares references, not content.
Not Equal
s1 is interned, s2 is a new object.
Trap 1: int
int is for integers.
Trap 2: byte
byte is for small integers.
Trap 3: String
String is a class, not primitive.
int
Why wrong: int is for integers.
byte
Why wrong: byte is for small integers.
char
char is a 16-bit Unicode character.
String
Why wrong: String is a class, not primitive.
Trap 1: The method can be overridden in a subclass.
Static methods cannot be overridden, only hidden.
Trap 2: The method can return an int.
main must be void for standard entry.
Trap 3: The method can be private.
Must be public to be accessible by JVM.
The method can be overridden in a subclass.
Why wrong: Static methods cannot be overridden, only hidden.
The method can return an int.
Why wrong: main must be void for standard entry.
The method can be called without creating an instance of the class.
It is static, so it belongs to the class.
The method can be private.
Why wrong: Must be public to be accessible by JVM.
Trap 1: int[][] array = new int[3,4];
Wrong syntax.
Trap 2: int[] array[] = new int[3][4];
Valid but unusual; still correct? Actually it is valid, but for clarity the standard is A. However, to avoid confusion, we make A the only correct.
Trap 3: int array[][] = new int[3,4];
Wrong syntax; comma not allowed.
int[][] array = new int[3,4];
Why wrong: Wrong syntax.
int[] array[] = new int[3][4];
Why wrong: Valid but unusual; still correct? Actually it is valid, but for clarity the standard is A. However, to avoid confusion, we make A the only correct.
int array[][] = new int[3,4];
Why wrong: Wrong syntax; comma not allowed.
int[][] array = new int[3][4];
Correct syntax.
Trap 1: 1
Boolean expression returns boolean.
Trap 2: true
Both conditions must be true.
Trap 3: 0
Boolean expression returns boolean.
1
Why wrong: Boolean expression returns boolean.
true
Why wrong: Both conditions must be true.
false
The second condition is false.
0
Why wrong: Boolean expression returns boolean.
Trap 1: enhanced for loop
May not execute if collection empty.
Trap 2: for loop
For loop may not execute if condition false.
Trap 3: while loop
While loop may not execute if condition false.
enhanced for loop
Why wrong: May not execute if collection empty.
do-while loop
Body executes first, then condition checked.
for loop
Why wrong: For loop may not execute if condition false.
while loop
Why wrong: While loop may not execute if condition false.
Trap 1: 2
2 is skipped.
Trap 2: Compilation error
Code compiles.
Trap 3: 123
2 is skipped.
2
Why wrong: 2 is skipped.
Compilation error
Why wrong: Code compiles.
13
1 and 3 are printed.
123
Why wrong: 2 is skipped.
Trap 1: public
Visible everywhere.
Trap 2: default (no modifier)
Visible within package.
Trap 3: protected
Visible in same package and subclasses.
public
Why wrong: Visible everywhere.
private
Only within the class.
default (no modifier)
Why wrong: Visible within package.
protected
Why wrong: Visible in same package and subclasses.
Trap 1: 3.33
Integer division truncates.
Trap 2: 0
Not exact division.
Trap 3: 3
That's the quotient.
3.33
Why wrong: Integer division truncates.
0
Why wrong: Not exact division.
3
Why wrong: That's the quotient.
1
Remainder is 1.
Trap 1: 123abc
Starts with digit.
Trap 2: 2ndPlace
Cannot start with digit.
Trap 3: my-var
Hyphen not allowed.
$money
$ is allowed.
123abc
Why wrong: Starts with digit.
_value
_ is allowed.
2ndPlace
Why wrong: Cannot start with digit.
my-var
Why wrong: Hyphen not allowed.
Trap 1: int x = 2.0;
Double cannot be assigned to int without cast.
Trap 2: int x = 0xG;
G is not hex digit.
int x = 2.0;
Why wrong: Double cannot be assigned to int without cast.
int x = 1_000;
Underscore allowed.
int x = 0xG;
Why wrong: G is not hex digit.
int x = 03;
Octal literal for 3.
int x = 0;
Valid.
Trap 1: for
Loop.
Trap 2: try
Exception handling.
Trap 3: while
Loop.
for
Why wrong: Loop.
switch
Multi-way branch.
try
Why wrong: Exception handling.
if
Conditional statement.
while
Why wrong: Loop.
Trap 1: It must return an int.
Must be void.
Trap 2: It can be overloaded.
Overloading is allowed but not a required statement.
It must be declared void.
No return value.
It must be declared static.
Called without instance.
It must be declared public.
Required for JVM access.
It must return an int.
Why wrong: Must be void.
It can be overloaded.
Why wrong: Overloading is allowed but not a required statement.
Refer to the exhibit.
public class Test {
public static void main(String[] args) {
int a = 10;
int b = 20;
System.out.println(a + b);
System.out.println("Sum: " + a + b);
}
}Trap 1: Runtime exception
No exception.
Trap 2: Compilation error
No error.
Trap 3: 30 Sum: 30
The second line would be Sum: 1020.
Runtime exception
Why wrong: No exception.
Compilation error
Why wrong: No error.
30 Sum: 1020
Correct.
30 Sum: 30
Why wrong: The second line would be Sum: 1020.
Refer to the exhibit.
public class LoopTest {
public static void main(String[] args) {
int count = 0;
for (int i = 0; i < 5; i++) {
if (i % 2 == 0) {
continue;
}
count++;
}
System.out.println(count);
}
}Trap 1: 3
i=5 not reached.
Trap 2: 5
Continue skips even numbers.
Trap 3: 0
Count increments for odd numbers.
3
Why wrong: i=5 not reached.
5
Why wrong: Continue skips even numbers.
2
Only i=1 and i=3 increment count.
0
Why wrong: Count increments for odd numbers.
Trap 1: ArrayList<Book>
Not a mapping structure; duplicates allowed.
Trap 2: LinkedList<String>
No mapping, inefficient search.
Trap 3: HashSet<String>
Only keys, no count.
ArrayList<Book>
Why wrong: Not a mapping structure; duplicates allowed.
LinkedList<String>
Why wrong: No mapping, inefficient search.
HashSet<String>
Why wrong: Only keys, no count.
HashMap<String, Integer>
Maps unique genre to count.
Trap 1: TreeSet<Transaction>
Sorted order, not insertion order.
Trap 2: LinkedList<Transaction>
Maintains order but slower iteration for large lists.
Trap 3: HashSet<Transaction>
No order guarantee.
TreeSet<Transaction>
Why wrong: Sorted order, not insertion order.
LinkedList<Transaction>
Why wrong: Maintains order but slower iteration for large lists.
HashSet<Transaction>
Why wrong: No order guarantee.
ArrayList<Transaction>
Maintains insertion order, fast iteration.
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