All Flashcards
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.
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!
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.