Let’s break this down line by line: CardBoard c1 = new CardBoard(); We now have two objects, the CardBoard c1 points at and the Short c1.story. Neither is available for GC as c1 points at the CardBoard and the story variable of the CardBoard points at the Short… CardBoard c2 = new CardBoard(); Similar to … Read more
Compile time error – the java compiler can’t compile the code, often because of syntax errors. Typical candidates: missing brackets missing semicolons access to private fields in other classes missing classes on the classpath (at compile time) Runtime error – the code did compile, can be executed but crashes at some point, like you have … Read more
Actually internal data structure of PriorityQueue is not ordered, it is a heap. PriorityQueue doesn’t need to be ordered, instead, it focuses on head of data. Insertion is in O(log n) time. Sorting wastes time and useless for a queue. Moreover, either the element is-a Comparable, or a Comparator is provided. Unfortunately, non-comparable checking is … Read more
You cannot cast between class loaders. Class identity is composed of fully qualified name and the class loader. Check class identity crysis here.
Although the override is done properly for SubCovariantTest the answer is 5 because of how the variable c1 is declared. It is declared as a CovariantTest and not as a SubCovariantTest. When c1.getObject().x is run, it does not know that it is a SubCovariantTest (no casting was used). This is why 5 is returned from … Read more
If you compile it with -Xlint you’ll get a warning: c:\Users\Jon\Test>javac -Xlint SneakyThrow.java SneakyThrow.java:9: warning: [unchecked] unchecked cast throw (T) ex; ^ required: T found: Throwable where T is a type-variable: T extends Throwable declared in method <T>sneakyThrowInner(Throwable) 1 warning That’s basically saying “This cast isn’t really checked at execution time” (due to type erasure) … Read more
A RuntimeException could be thrown by any code. In other words, the compiler can’t easily predict what kind of code can throw it. A RuntimeException can be caught by a catch(Exception e) block. IOException, however, is a checked exception – only method calls which are declared to throw it can do so. The compiler can … Read more
“Fred” and “47” will come from the string literal pool. As such they won’t be created when the method is invoked. Instead they will be put there when the class is loaded (or earlier, if other classes use constants with the same value). “Fred47”, “ed4” and “ED4” are the 3 String objects that will be … Read more
Here is a list of connecting characters. These are characters used to connect words. http://www.fileformat.info/info/unicode/category/Pc/list.htm U+005F _ LOW LINE U+203F ‿ UNDERTIE U+2040 ⁀ CHARACTER TIE U+2054 ⁔ INVERTED UNDERTIE U+FE33 ︳ PRESENTATION FORM FOR VERTICAL LOW LINE U+FE34 ︴ PRESENTATION FORM FOR VERTICAL WAVY LOW LINE U+FE4D ﹍ DASHED LOW LINE U+FE4E ﹎ CENTRELINE … Read more
NaN means “Not a Number”. Java Language Specification (JLS) Third Edition says: An operation that overflows produces a signed infinity, an operation that underflows produces a denormalized value or a signed zero, and an operation that has no mathematically definite result produces NaN. All numeric operations with NaN as an operand produce NaN as a … Read more