Writing Constructors

Introduction: 5.2.0

• constructors set intial values for an object’s instance variables
  • written after the instance variables and before methods
  • typically public
    • sidenote: not true for singleton design, something we use in robotics!
  • public ClassName()
  • they don’t have a return type
  • can intake parameters, which help to initialize values!
  • Must be the same name as the class!
• Classes usually have more than one constructor
  • has one with no parameters
  • has one which takes in parameters
  • this is known as overloading the constructor

public class House {
    String address;
    Color paintColor;

    public House(String add, Color pColor) {
        address = add;
        paintColor = pColor;
    }

    public House() {
        this("123 street street", Color.orange);  
        // this calls the above constructor instead of repeating a bunch of code
    }
}

• if there are no constructors, java provides a default constructor
  • Instance variables are set to default values
  • objects are set to null!
  • Java will not do this if you explicitly define a constructor

Objects as parameters

• when you pass object references as parameters, these variables become aliases to the original object
  • They can modify it!
  • you need to copy the object into the parameters of a new object to avoid modifying this reference

Summary: 5.2.2

• Constructors are used to set the initial state of an object
• When no constructor is provides, java provides a no-argument default constructor
• Constructor parameters are local variables to the constructor