Cheat Sheet

This cheat sheet contains the most important takeaways that lead up to section seven.

Definitions

• Class: blueprint from which you can create objects.

• Object: an object is a thing that you can see or describe.

• Field: class variable that describes an object.

• Action: method (function) that represents what the object can do.

• Constructor: runs when you create a new object.

  • Purpose: update every field of the newly created object.

• this: refers to the current object that's calling the constructor or method.

  • Purpose: useful when fields and parameters have conflicting names.

• Copy Constructor: runs when you create an object.

  • Purpose: copy every value from a source object into a new object.

• Getter: method (function) that returns a copy of a private field's value.

• Setter: method (function) that updates the value of a private field.

• toString: method that returns a String representation of every field in an object.

  • Purpose: When you print an object, Java internally calls the toString method.

public vs. private

• public: provides public access to a field or method from anywhere.

  • Constructors and methods tend to be public.

• private: prevents direct access of a field or method outside of its class.

  • To protect the state of an object, fields tend to be private.

The Big Three

If a class has fields, you need to add:

1. Constructor -- to update the fields of a new object.

2. Getters -- to get the value of a private field.

3. Setters -- to set the value of a private field.

Reference Traps

The state of a variable should not change because you updated another.

Falling into a reference trap can:

1. lead to unpredictable behavior.

2. lead to variables changing when you don't expect them to.

3. leave you wondering: why is my code doing this?

Primitive vs. Class Types.

Examples of primitives types are int, long, char and boolean.

Examples of class types that we created objects from are: Scanner, Dealership, Car.

Tips and Tricks.

• Syntax to directly pass an array into a method: new String[] { element, element }

• Syntax to directly return an array: return new String[] { element, element }

• You can autocomplete getters and setters in Visual Studio Code.