hardprimitives and char width
What value of i is printed after two post-increments?
int i = 5; int s = i++ + i++; System.out.println(i);Java Interview Questions (541 to practise)
Java runs a very large share of enterprise back ends. Its interviews reward knowing the memory model as well as the syntax.
Collections behaviour, equals and hashCode contracts, string interning, checked versus unchecked exceptions, stream laziness, and the concurrency primitives.
- Total questions
- 541
- Easy
- 112
- Medium
- 211
- Hard
- 218
Where it shows up: Banking, large-scale services, Android, and any company running Spring in production.
Sample Java questions
Twenty real Java questions from the library, code snippet included. Nothing here is paraphrased for search engines. It is the same text a signed-in user sees.
mediumstream pipelines
Which list is produced by mapping toLowerCase?
List<String> r = Stream.of("A","B","C").map(String::toLowerCase).toList();mediumpattern matching switch instanceof
Using record deconstruction patterns, what does `format(new Point(1, 2))` print?
record Point(int x, int y) {}
static String format(Object o) {
return switch (o) {
case Point(int x, int y) -> "x+y=" + (x + y);
default -> "?";
};
}mediumif switch loops
What does this code print?
int x = 5;\nx = x++;\nSystem.out.println(x);hardLambdas and method refs
What does this code do?
List<Supplier<Integer>> ss = new ArrayList<>();\nfor (int i = 0; i < 3; i++) { ss.add(() -> i); }medium== vs equals
What does this code print?
String a = new String("x");\nString b = new String("x");\nSystem.out.println(a.equals(b));mediumif switch loops
What does this code print?
int x;\nif (false) x = 5;\nSystem.out.println(x);mediumCompletableFuture composition
What does this code print?
CompletableFuture<Integer> f = CompletableFuture.completedFuture(5);\nSystem.out.println(f.get());mediumprimitives and char width
What does this code print?
int[] a = new int[0];\nSystem.out.println(a.length);mediumstream pipelines
What does this code print?
System.out.println(List.of(1, 2));mediumLambdas and method refs
What does this code print?
class A { static String f() { return "A"; } }\nclass B extends A { static String f() { return "B"; } }\nA a = new B();\nSystem.out.println(a.f());mediumstream pipelines
What does this code print?
long c = Stream.of("a","b","c").filter(s -> s.equals("b")).count();\nSystem.out.println(c);hardstream pipelines
What does this code print?
List<Integer> list = new ArrayList<>(List.of(1,2,3,4));\nIterator<Integer> it = list.iterator();\nwhile (it.hasNext()) { if (it.next() % 2 != 0) it.remove(); }\nSystem.out.println(list);hardtry-with-resources
What does this code print?
static int f() {\n try { return 1; } finally { return 2; }\n}\nSystem.out.println(f());hardfunctional interfaces
What does this code do?
interface I1 { default int f() { return 1; } }\ninterface I2 { default int f() { return 2; } }\nclass C implements I1, I2 {}\nnew C().f();hardComparator comparing thenComparing
What does this code throw?
List<String> list = List.of("b","a");\nlist.sort(null);hardstream pipelines
What does this code print?
System.out.println(Stream.of(1,2,3).filter(i -> i<2).findFirst().orElse(0));hardmain entry point
What does this code print?
class A { static String f() { return "A"; } }\nclass B extends A { static String f() { return "B"; } }\nA a = new B();\nSystem.out.println(a.f());hardif switch loops
What does this code throw?
static int f(int n) { return f(n - 1); }\nf(5);mediumstream pipelines
What does this code print?
System.out.println(IntStream.range(0,3).reduce(0, Integer::sum));Sign in to answer
Everything above is free to read. Answering needs a free account.
We keep the correct answer, the explanation and the scoring behind sign-in so the platform stays honest, which is why the answer options and the worked explanation for every Java question stay behind a free account. Signing in is free and takes a few seconds.
Java topics covered
44 distinct Java topics are tagged across the library. These are the real topic labels stored on the questions, not a hand-written list.
- stream pipelines (36)
- primitives and char width (25)
- if switch loops (23)
- try-with-resources (23)
- main entry point (22)
- final and constants (22)
- class loading delegation (20)
- String.intern and pool (19)
- sealed types usage (17)
- ExecutorService usage (16)
- functional interfaces (16)
- CompletableFuture composition (15)
- pattern matching switch instanceof (15)
- bytecode and operand stack (14)
- HashMap internals treeify (13)
- records and compact constructors (12)
- AQS internals (12)
- ConcurrentHashMap (12)
- ZGC vs G1 (12)
- Collectors toMap groupingBy (12)
- Optional patterns (11)
- Comparator comparing thenComparing (11)
- synchronized monitors biased locks (11)
- virtual threads carrier pinning (10)
- final-field publication (10)
- volatile semantics (9)
- Lambdas and method refs (9)
- reflection cost (9)
- ThreadLocal lifecycle leaks (9)
- JIT HotSpot tiered (9)
- Integer caching identity (8)
- == vs equals (8)
- BigDecimal (8)
- annotations and retention (8)
- JMM happens-before (8)
- escape analysis scalar replacement (8)
- object headers compressed oops (7)
- G1GC regions (7)
- Duration vs Period (6)
- generics bounds wildcards PECS (5)
- generics (4)
- EnumSet EnumMap (4)
- Generics (bounds/wildcards/PECS) (2)
- send and public_send (1)
Search and filter every Java question
…
Difficulty