1. Lesson: Language Basics
  2. Variables
    1. Naming
    2. Primitive Data Types
    3. Default Values
    4. Literals
    5. Using Underscore Characters in Numeric Literals
    6. Arrays
    7. Declaring a Variable to Refer to an Array
    8. Creating, Initializing, and Accessing an Array
    9. Copying Arrays
    10. Summary of Variables
    11. Questions and Exercises: Variables
  3. Expressions, Statements, and Blocks
    1. Expressions
    2. Statements
    3. Blocks
    4. Questions and Exercises: Expressions, Statements, and Blocks
  4. Control Flow Statements
    1. The if-then Statement
    2. The if-then-else Statement
    3. The switch Statement
    4. Using Strings in switch Statements
    5. The while and do-while Statements
    6. The for Statement
    7. The break Statement
    8. The continue Statement
    9. The return Statement
    10. Summary of Control Flow Statements
    11. Questions and Exercises: Control Flow Statements
  5. Lesson: Classes and Objects
    1. Classes
    2. Declaring Classes
    3. Declaring Member Variables
    4. Access Modifiers
    5. Types
    6. Variable Names
    7. Defining Methods
    8. Naming a Method
    9. Overloading Methods
    10. Providing Constructors for Your Classes
    11. Passing Information to a Method or a Constructor
    12. Parameter Types
    13. Arbitrary Number of Arguments
    14. Parameter Names
    15. Passing Primitive Data Type Arguments
    16. Passing Reference Data Type Arguments
    17. Objects
    18. Creating Objects
    19. Declaring a Variable to Refer to an Object
    20. Instantiating a Class
    21. Initializing an Object
    22. Using Objects
    23. Referencing an Object's Fields
    24. Calling an Object's Methods
    25. The Garbage Collector
    26. More on Classes
    27. Returning a Value from a Method
    28. Returning a Class or Interface
    29. Using the this Keyword
    30. Using this with a Field
    31. Using this with a Constructor
    32. Controlling Access to Members of a Class
    33. Understanding Instance and Class Members
    34. Class Variables
    35. Class Methods
    36. Constants
    37. The Bicycle Class
    38. Initializing Fields
    39. Static Initialization Blocks
    40. Initializing Instance Members
    41. Summary of Creating and Using Classes and Objects
    42. Questions and Exercises: Classes
    43. Questions and Exercises: Objects
  6. Nested Classes
    1. Why Use Nested Classes?
    2. Static Nested Classes
    3. Inner Classes
    4. Inner Class Example
    5. Local and Anonymous Inner Classes
    6. Modifiers
    7. Summary of Nested Classes
    8. Questions and Exercises: Nested Classes
  7. Enum Types
    1. Questions and Exercises: Enum Types
  8. Annotations
    1. Documentation
    2. Annotations Used by the Compiler
    3. Annotation Processing
    4. Questions and Exercises: Annotations
  9. Lesson: Interfaces and Inheritance
    1. Interfaces
    2. Interfaces in Java
    3. Interfaces as APIs
    4. Interfaces and Multiple Inheritance
    5. Defining an Interface
    6. The Interface Body
    7. Implementing an Interface
    8. A Sample Interface, Relatable
    9. Implementing the Relatable Interface

5.16.Passing Reference Data Type Arguments #

Reference data type parameters, such as objects, are also passed into methods by value. This means that when the method returns, the passed-in reference still references the same object as before. However, the values of the object’s fields can be changed in the method, if they have the proper access level.
For example, consider a method in an arbitrary class that moves Circle objects:

public void moveCircle(Circle circle, int deltaX, int deltaY) {
    // code to move origin of circle to x+deltaX, y+deltaY
    circle.setX(circle.getX() + deltaX);
    circle.setY(circle.getY() + deltaY);
	
    //code to assign a new reference to circle
    circle = new Circle(0, 0);
}

Let the method be invoked with these arguments:
moveCircle(myCircle, 23, 56)
Inside the method, circle initially refers to myCircle. The method changes the x and y coordinates of the object that circle references (i.e., myCircle) by 23 and 56, respectively. These changes will persist when the method returns. Then circle is assigned a reference to a new Circle object with x = y = 0. This reassignment has no permanence, however, because the reference was passed in by value and cannot change. Within the method, the object pointed to by circle has changed, but, when the method returns, myCircle still references the same Circle object as before the method was called.

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