Lab: choosing the right types for Movie

☕ Java 17 · Two Kinds of Data: Primitives and References · 3/3

Goal: design the fields of our Movie class, choosing a type for each piece of data and explaining why.

Setup: create com/netflix/model/Movie.java under your source folder.

Step 1 — Reference fields

package com.netflix.model;

public class Movie {
    // Reference types (default: null)
    private String title;
    private String genre;
}

Text is an object in Java, so String is a reference type. A movie whose genre isn't set yet simply has genre == null.

Step 2 — Primitive fields

    // Primitive types (default: 0 / false)
    private int releaseYear;
    private double rating;
    private float storageSizeGB;
    private long totalViews;
    private boolean isAvailable;

Field	Type	Why
releaseYear	int	a whole number, far below 2 billion
rating	double	needs decimals (9.3)
storageSizeGB	float	decimals, but little precision needed
totalViews	long	a hit show passes 2 billion views: an int would overflow
isAvailable	boolean	available or not, nothing in between

Step 3 — A summary method

    public void printSummary() {
        var label = title + " (" + releaseYear + ")";
        var stars = rating >= 8.0 ? "Top Rated" : "Standard";
        System.out.println(label + " — " + stars);
        System.out.println("Views: " + totalViews);
    }

var lets the compiler infer a local variable's type from its value: both label and stars are String. (condition ? a : b picks a if the condition is true, b otherwise.) Next section covers var in detail.

Step 4 — Run it

    public static void main(String[] args) {
        Movie movie = new Movie();
        movie.title = "Stranger Things";
        movie.genre = "Sci-Fi";
        movie.releaseYear = 2016;
        movie.rating = 9.3;
        movie.storageSizeGB = 4.2f;
        movie.totalViews = 1_500_000_000L;
        movie.isAvailable = true;
        movie.printSummary();
    }

Remove the f from 4.2f and it no longer compiles: 4.2 is a double.

$ javac com/netflix/model/Movie.java
$ java com.netflix.model.Movie
Stranger Things (2016) — Top Rated
Views: 1500000000

Full code on GitHub

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