1. Value Types and Reference Types
In Java . . .
Value Types and Reference Types

2. Value Types
Variables contain the values of primitive data types

3. Value types of variables contain their values
In Java, primitive data types such as int, float, double, char, and boolean are called value types
A variable of one of these types is a container for one value of its appropriate type
counter
price
foundIt 7
5.99
false
Value types of variables contain their values

4. Value Types
Because a variable of a value type is a container for ONE value of the corresponding type, giving it a second value replaces the first value entirely with the second
dependents 2
dependents

5. Reference Types in Java
Objects of Classes

6. Reference Types
A variable declared as a reference to an object of some class (either a built-in class or a user-defined class) is a reference type
A reference variable DOES NOT contain the the object to which it refers – instead, it refers to that object (i.e., it points to that object)
A reference variable is null (refers to nothing) until it is given an object for it to reference
Actual Object
Reference

7. Reference Types personA null personB null
Called a shallow copy because only the reference is copied
new creates an actual object of type Person initialized to Rachel Walling
Rachel Walling
personA
personB
Two different references now refer to a single actual object

8. Reference types
Just as value types may only have one value at a time, reference types may only refer to one actual instance at a time
Bob Smith
After line 5
bob

9. Reference types
As value types may only have one value at a time, reference types may only refer to one actual instance at a time
Since nothing refers to this object now, it is destroyed (“garbage collected”) by Java
Bob Smith
bob
Bob Jones
After line 7