All Flashcards
How are wrapper classes used in data validation?
Wrapper classes can be used to represent nullable values in databases, which can be useful when a field is not required.
How are wrapper classes used in generic data structures?
Generic data structures like ArrayList<Integer> require objects, so wrapper classes are used to store primitive data.
What are the differences between Integer.parseInt() and the Integer constructor?
Integer.parseInt() parses a String to an int. The Integer constructor creates an Integer object from an int or String.
What are the differences between Double.parseDouble() and the Double constructor?
Double.parseDouble() parses a String to a double. The Double constructor creates a Double object from a double or String.
What does the following code output?
Integer num = new Integer(10); int val = num.intValue(); System.out.println(val);
10
What does the following code output?
Double num = new Double(3.14); double val = num.doubleValue(); System.out.println(val);
3.14
What does the following code output?
Integer num = 5; int val = num; System.out.println(val);
5
What does the following code output?
Double num = 2.718; double val = num; System.out.println(val);
2.718
What does the following code output?
Integer num = null; int val = 0; try { val = num; } catch (NullPointerException e) { System.out.println("NullPointerException caught!"); }
NullPointerException caught!