All Flashcards
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!
What is a wrapper class?
A class that encapsulates a primitive data type, allowing it to be treated as an object.
What is the Integer class?
A wrapper class for the primitive type int.
What is the Double class?
A wrapper class for the primitive type double.
What is autoboxing?
The automatic conversion of a primitive type to its corresponding wrapper class object.
What is unboxing?
The automatic conversion of a wrapper class object to its corresponding primitive type.
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.