All Flashcards
Why use wrapper classes?
To use primitive types in contexts that require objects, such as collections or methods expecting objects.
Can Integer objects be null?
Yes, unlike the primitive int, an Integer object can be assigned a null value.
What is the purpose of the intValue() method?
It returns the int value of an Integer object.
What is the purpose of the doubleValue() method?
It returns the double value of a Double object.
Why are wrapper classes useful with collections?
Collections like ArrayList can only store objects, not primitive types. Wrapper classes allow you to store primitive data in collections.
What is the difference between int and Integer?
int is a primitive type; Integer is a class that wraps the int type. Integer can be null, int cannot.
What is the difference between double and Double?
double is a primitive type; Double is a class that wraps the double type. Double can be null, double cannot.
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!